777F MG Sistemas [PDF]

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SERV18XX December 2006



GLOBAL SERVICE LEARNING TECHNICAL PRESENTATION



777F (JRP) OFF-HIGHWAY TRUCK POWER TRAIN, STEERING, HOIST, AND BRAKING SYSTEMS



Service Training Meeting Guide (STMG)



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TABLE OF CONTENTS POWER TRAIN ...........................................................................................................................3 Torque Converter Hydraulic System ......................................................................................6 Transmission Hydraulic System ...........................................................................................17 Rear Axle ..............................................................................................................................29 Transmission/Chassis Electronic Control System ................................................................31 STEERING SYSTEM ................................................................................................................42 HOIST SYSTEM ........................................................................................................................57 BRAKE SYSTEM ......................................................................................................................77 Brake Electronic Control System .......................................................................................104 Automatic Retarder Control System...................................................................................109 Traction Control System .....................................................................................................111 CONCLUSION.........................................................................................................................118



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POWER TRAIN The 777F Off-highway Truck power train is electronically controlled. The Transmission/Chassis ECM controls the ECPC transmission shifting and the torque converter lockup clutch operation. The transmission has seven forward speeds and one reverse speed. Power flows from the engine to the rear wheels through the power train. The main power train components are: - Torque converter (1) - Drive shaft (2) - Transfer gears (3) - Transmission (4) - Differential (5) - Final drives (6) Other power train components visible in this illustration are the transmission charge filters (7), torque converter charging filter (8), and two-section hydraulic tank (9).



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2 These illustrations show the location of the main electronic components in the power train. The Transmission/Chassis ECM (1) is located behind the cab seat and is accessed by removing a panel at the rear of the cab. The transmission modulating valves (2) are located on top of the transmission planetary gears and are accessed by removing a cover plate. The torque converter lockup clutch solenoid valve (3) is located on the rear of the torque converter. NOTE: The Transmission/Chassis ECM receives input signals from several components located on the machine to control transmission shifting and the torque converter lockup clutch operation. The electronic components will be covered later in the presentation.



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Torque Converter Outlet Relief Valve



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POWER TRAIN HYDRAULIC SYSTEM



To Brake Cooling



To Variable Speed Clutch Control



To To Hoist Pilot Traction Signal Control Resolver Pilot



Transmission Charge Filters



Lockup Valve



Torque Converter



Lockup Clutch Relief Valve



Lockup Clutch Valve Filter Torque Converter Charge Filter



To Brake Cooling



Hydraulic Controls



Transmission Torque Converter Inlet Relief Valve



Transmission Oil Level Switch



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Shown is the transmission and torque converter hydraulic system for the 777F. A five section pump is located at the rear of the torque converter housing. The first section (attached to pump drive at rear of torque converter) scavenges oil from the bottom of the torque converter case and returns the oil to the hoist, torque converter, and brake hydraulic tank. The second section pumps charge oil through the torque converter filter to the torque converter. The third section sends oil through the lockup clutch filter and provides pilot oil to the following circuits: - Lockup clutch valve - Variable speed fan clutch control - Hoist pilot signal resolver - Traction control valve The fourth section scavenges oil from the transmission sump and sends oil to the transmission oil cooler and the transmission hydraulic tank. The fifth section sends charge oil through the transmission oil filters to the transmission control valves.



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TORQUE CONVERTER HYDRAULIC SYSTEM To Brake Cooling



Torque Converter Charging Filter To Brake Cooling



Inlet Relief Valve Outlet Relief Valve



Lockup Relief Valve To Variable Speed Fan To TCS Clutch Valve Control



Lockup Clutch Valve



Lockup Clutch Filter



To Hoist Pilot Signal Resolver



Converter Scavenge Screen



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Torque Converter Hydraulic System This schematic shows the oil flow from the torque converter pump through the torque converter hydraulic system. The scavenge pump section pulls oil through a screen from the torque converter housing and sends the oil to the hoist, torque converter, and brake hydraulic tank. The torque converter charging pump section sends oil through the torque converter charging filter to the torque converter inlet relief valve. Oil flows from the inlet relief valve through the torque converter to the outlet relief valve. Oil flows from the outlet relief valve to the brake oil cooling circuit. The lockup clutch valve pump section sends oil through the lockup clutch valve filter to the torque converter lockup clutch valve. When oil pressure in the lockup clutch valve circuit is too high, the lockup clutch relief valve allows oil to flow to the brake cooling circuit. Oil from the lockup clutch valve pump section also flows to the TCS valve, variable speed clutch control and hoist pilot signal resolver.



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The five sections of the power train pump (from the front to the rear) are: - Torque converter scavenge (1) - Torque converter charging (2) - Lockup clutch valve, hoist pilot circuit, TCS valve, and variable speed fan clutch (3) - Transmission scavenge (4) - Transmission charging (5)



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Lockup Piston



Turbine



Impeller



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TORQUE CONVERTER CONVERTER DRIVE



Stator



Torque Converter Inlet Oil



6



Freewheel Assembly



Torque Converter Lockup Oil Passage



This sectional view shows a torque converter in CONVERTER DRIVE. The lockup clutch (yellow piston and blue discs) is not engaged. During operation, the rotating housing and impeller (red) can rotate faster than the turbine (blue). The stator (green) remains stationary and multiplies the torque transfer between the impeller and the turbine. The output shaft rotates slower than the engine crankshaft, but with increased torque. Lockup Piston



Turbine



Impeller



TORQUE CONVERTER DIRECT DRIVE



Stator



Torque Converter Inlet Oil



7



Freewheel Assembly



Torque Converter Lockup Oil Passage



In DIRECT DRIVE, the lockup clutch is engaged by hydraulic pressure and locks the turbine to the impeller. The housing, impeller, turbine, and output shaft then rotate as a unit at engine rpm. The stator, which is mounted on a one-way clutch, is driven by the force of the oil in the housing. The one-way clutch permits the stator to turn freely in DIRECT DRIVE when torque multiplication is not required.



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The five section power train pump (1) is located at the bottom rear of the torque converter. The inlet relief valve (2) limits the maximum pressure of the supply oil to the torque converter. The torque converter inlet relief pressure can be checked by removing a plug and installing a pressure tap. Normally, the inlet relief pressure will be slightly higher than the outlet relief valve pressure. Oil flows through the inlet relief valve and enters the torque converter. Some of the oil will leak through the torque converter to the bottom of the housing to be scavenged. Most of the oil in the torque converter is used to provide a fluid coupling and flows through the torque converter outlet relief valve (3).



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The outlet relief valve maintains the minimum pressure inside the torque converter. The main function of the outlet relief valve is to keep the torque converter full of oil to prevent cavitation. The outlet relief pressure can be measured at the tap (4) on the outlet relief valve. The torque converter lockup clutch valve (5) directs oil to engage the torque converter lockup clutch. The torque converter lockup clutch pressure can be checked at the tap (6) on top of the lockup clutch valve. Excess oil that accumulates in the bottom of the torque converter is scavenged by the first section of the pump through a screen behind the access cover (7) and returned to the hoist, torque converter, and brake hydraulic tank.



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LOCKUP CLUTCH MODULATING VALVE TORQUE CONVERTER DRIVE Lockup Clutch Pressure Tap



T/C Lockup Solenoid To Lockup Clutch



From Lockup Clutch Pump



10 The torque converter lockup clutch modulating valve contains a proportional solenoid that receives a signal from the Transmission/Chassis ECM to engage and release the torque converter lockup clutch. In this illustration, the lockup clutch modulating valve is shown with no current signal applied to the solenoid (TORQUE CONVERTER DRIVE or NEUTRAL). The Transmission/Chassis ECM controls the rate of oil flow through the lockup clutch modulating valve to the lockup clutch by changing the signal current strength to the solenoid. With no current signal applied to the solenoid, the transmission modulating valve is DE-ENERGIZED and oil flow to the clutch is blocked. Pump oil flows into the valve body around the valve spool and into a drilled passage in the center of the valve spool. The oil flows through the drilled passage and orifice to the left side of the valve spool to a drain orifice. Since there is no force acting on the pin assembly to hold the ball against the drain orifice, the oil flows through the spool and the drain orifice past the ball to the tank. The spring located on the right side of the spool in this view holds the valve spool to the left. The valve spool opens the passage between the clutch passage and the tank passage and blocks the passage between the clutch passage and the pump supply port. Oil flow to the clutch is blocked. Oil from the clutch drains to the tank preventing clutch engagement.



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LOCKUP CLUTCH MODULATING VALVE DIRECT DRIVE



Lockup Clutch Pressure Tap



T/C Lockup Solenoid To Lockup Clutch



From Lockup Clutch Pump



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In this illustration, the modulating valve is shown with a maximum current signal commanded to the solenoid. When the modulation cycle stops, the Transmission/Chassis ECM sends the maximum specified current signal to fully engage the lockup clutch (DIRECT DRIVE). The constant current signal pushes the pin firmly against the ball in the solenoid valve. The pin force against the ball blocks more oil from flowing through the drain orifice. This restriction causes an increase in pressure on the left side of the valve spool. The valve spool moves to the right to allow pump flow to fully engage the clutch. In a short period of time, maximum pressure is felt at both ends of the proportional solenoid valve spool. This pressure along with the spring force on the right end of the spool cause the valve spool to move to the left until the forces on the right end and the left end of the valve spool are balanced. The valve spool movement to the left (balanced) position reduces the flow of oil to the engaged clutch. The Transmission/Chassis ECM sends a constant maximum specified current signal to the solenoid to maintain the desired clutch pressure.



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A torque converter outlet temperature sensor (arrow) provides an input signal to the Transmission/Chassis ECM, which sends a signal to the monitoring system to inform the operator of the torque converter outlet temperature.



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Oil from the lockup clutch valve pump section flows to the lockup valve oil filter (1) and then to the lockup clutch modulating valve (2). The filter is located inside of the left frame rail.



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The filter has a bypass switch (3) which provides an input signal to the monitoring system, via the Transmission/Chassis ECM, to inform the operator if the filter is restricted. The filter housing has an S•O•S tap (4) and a lockup clutch circuit pressure tap (5).



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The lockup clutch relief valve (1) is located inside the left frame rail in front of the lockup clutch filter (2). This view is looking up from the bottom of the truck. When oil pressure in the lockup clutch valve circuit is too high, the lockup clutch relief valve allows oil to flow to the brake cooling circuit.



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The torque converter charging filter (1) is located on the right frame rail, behind the right front tire. Oil from the torque converter charging pump section flowS through the torque converter filter to the torque converter inlet relief valve.



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The torque converter filter includes an S•O•S port (2) located on the bottom of the filter.



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TRANSMISSION HYDRAULIC SYSTEM NEUTRAL



Transmission Oil Temperature Sensor



1



5



Bypass Switch Transmission Cooler



Transmission Charge Pump



Transmission Scavenge Pump



2 6



Screen Screen Transmission Sump



Transmission Hydraulic Tank



Main Relief Valve



Transmission Lube Relief Valve



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Transmission Hydraulic System The transmission scavenge pump section pulls oil from the bottom of the transmission case through a magnetic screen and sends the oil through the transmission oil cooler to the transmission tank. The magnetic screen should always be checked for debris if a problem with the transmission is suspected. The transmission charging pump section pulls oil from the transmission hydraulic tank. Charging oil flows from the pump through two transmission charging filters to the transmission main relief valve and seven modulating valves. The main relief valve regulates the supply pressure inside the transmission hydraulic system. Oil unseats the check ball and forces the spool to the right if the transmission system pressure becomes greater than the spring force on the right of the spool. Excess oil will flow to the lubrication circuit and the lube relief valve. The lubrication circuit oil and oil from the lube relief valve flows to the transmission sump. The relief valve is adjustable by turning the adjusting screw on the right end of the valve.



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The clutch modulating valves control the engagement of the transmission clutches. The solenoids are controlled by a pulse width modulated (PWM) signal from the Transmission/Chassis ECM. Supply oil flows into the clutch modulating valves and through a passage in the center of the spool. Oil then flows to the tank if the solenoid is not energized. Oil flow is blocked by a ball and seat if the solenoid is energized. The spool will shift down and the clutch will begin to fill. The signal from the Transmission/Chassis ECM determines how long it takes to fill each clutch. The transmission lubrication relief valve limits the transmission lubrication oil pressure.



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The transmission scavenge pump section (1) pulls oil from the bottom of the transmission case through a magnetic screen and sends the oil through the transmission oil cooler (2) to the transmission tank. The oil cooler is located on the right side of the engine. The transmission charging pump section (3) pulls oil from the bottom of the transmission hydraulic tank through a magnetic screen and sends the oil through the transmission filters to the transmission hydraulic controls.



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21 Oil from the transmission charging pump section is sent to the transmission charge oil filters (1) located on the cross member on the right side of the machine. The rear filter housing has an S•O•S tap (2) and a charge pressure tap (3). The rear filter housing also has a bypass switch (4) which provides an input signal to the monitoring system, via the Transmission/Chassis ECM, to inform the operator if the filter is restricted. The ECPC transmission hydraulic controls can be accessed by removing a cover plate (5) on top of the transmission. The transmission input speed sensor (6) is located on top of the transfer gear housing. The transmission input speed sensor sends an input to the Transmission/Chassis ECM which checks the speed of the drive shaft to the speed of the engine. The transmission has pressure taps located on the outside of the transmission which aids in preventing contamination from entering the transmission as well as saving time when checking the pressures on the 777F transmission. Shown in the lower right illustration are the transmission control valve pressure taps. The lube oil pressure tap (7) and the transmission hydraulic system pressure tap (8) are located toward the rear of the transmission. Oil pressure for the seven clutches can be checked at the remaining seven taps (9) on the transmission.



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The transmission modulating valves control the oil to corresponding transmission clutches. The solenoid valves are: - Clutch No. 1 Solenoid valve (1) - Clutch No. 2 Solenoid valve (2) - Clutch No. 3 Solenoid valve (3) - Clutch No. 4 Solenoid valve (4) - Clutch No. 5 Solenoid valve (5) - Clutch No. 6 Solenoid valve (6) - Clutch No. 7 Solenoid valve (7) The main relief valve (8) controls the transmission hydraulic pressure, and the lubrication relief valve (not visible) controls the lubrication pressure. The lubrication relief valve is located below the main relief valve. Also located on the transmission hydraulic control valve is the transmission hydraulic oil temperature sensor (9). The temperature sensor sends a signal to the Transmission/Chassis ECM indicating transmission oil temperature.



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ENGAGEMENT OF TRANSMISSION CLUTCHES Transmission Speed



Engaged Clutches in the Transmission



NEUTRAL



1



REVERSE



1 and 7



FIRST speed



2 and 6



SECOND speed



1 and 6



THIRD speed



3 and 6



FOURTH speed



1 and 5



FIFTH speed



3 and 5



SIXTH speed



1 and 4



SEVENTH speed



3 and 4



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The table in this illustration lists the solenoids that are energized and clutches that are engaged for each transmission speed. This table can be useful for transmission diagnosis.



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TRANSMISSION MODULATING VALVE NO COMMANDED SIGNAL Test Port Valve Spool



Ball Orifice



Solenoid



Pin



Drain Orifice



To Tank



To Clutch



Spring



From Pump



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In this illustration, the transmission modulating valve is shown with no current signal applied to the solenoid. The Transmission/Chassis ECM controls the rate of oil flow through the transmission modulating valves to the clutches by changing the signal current strength to the solenoid. With no current signal applied to the solenoid, the transmission modulating valve is DE-ENERGIZED and oil flow to the clutch is blocked. Pump oil flows into the valve body around the valve spool and into a drilled passage in the center of the valve spool. The oil flows through the drilled passage and orifice to the left side of the valve spool to a drain orifice. Since there is no force acting on the pin assembly to hold the ball against the drain orifice, the oil flows through the spool and the drain orifice past the ball to the tank. The spring located on the right side of the spool in this view holds the valve spool to the left. The valve spool opens the passage between the clutch passage and the tank passage and blocks the passage between the clutch passage and the pump supply port. Oil flow to the clutch is blocked. Oil from the clutch drains to the tank preventing clutch engagement.



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TRANSMISSION MODULATING VALVE COMMANDED SIGNAL BELOW MAXIMUM Test Port Ball



Solenoid



Pin



Drain Orifice



Valve Spool



Orifice



To Tank



To Clutch



Spring



From Pump



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In this illustration, the modulating valve is shown with a signal to the solenoid that is below the maximum current. Clutch engagement begins when the Transmission/Chassis ECM sends an initial current signal to ENERGIZE the solenoid. The amount of commanded current signal is proportional to the desired pressure that is applied to the clutch during each stage of the engagement and disengagement cycle. The start of clutch engagement begins when the current signal to the solenoid creates a magnetic field around the pin. The magnetic force moves the pin against the ball in proportion to the strength of the current signal from the Transmission/Chassis ECM. The position of the ball against the orifice begins to block the drain passage of the oil flow from the left side of the valve spool to the tank. This partial restriction causes the pressure at the left end of the valve spool to increase. The oil pressure moves the valve spool to the right against the spring. As the pressure on the right side of the valve spool overrides the force of the spring, the valve spool shifts to the right. The valve spool movement starts to open a passage on the right end of the valve spool for pump supply oil to fill the clutch. Oil also begins to fill the spring chamber on on the right end of the spool.



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In the initial clutch filling stage, the Transmission/Chassis ECM commands a high current pulse to quickly move the valve spool to start filling the clutch. During this short period of time, the clutch piston moves to remove the clearances between the clutch discs and plates to minimize the amount of time required to fill the clutch. The ECM then reduces the current signal which reduces the pressure setting of the proportional solenoid valve. The change in current signal reduces the flow of oil to the clutch. The point where the clutch plates and discs start to touch is called TOUCH-UP. Once TOUCH-UP is obtained, the Transmission/Chassis ECM begins a controlled increase of the current signal to start the MODULATION cycle. The increase in the current signal causes the ball and pin to further restrict oil through the drain orifice to tank causing a controlled movement of the spool to the right. The spool movement allows the pressure in the clutch to increase. During the MODULATION cycle, the valve spool working with the variable commanded current signal from the Transmission/Chassis ECM acts as a variable pressure reducing valve. The sequence of partial engagement is called desired slippage. The desired slippage is controlled by the application program stored in the Transmission/Chassis ECM.



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TRANSMISSION MODULATING VALVE COMMANDED SIGNAL AT MAXIMUM Test Port Ball



Solenoid



Pin



Drain Orifice



Valve Spool



Orifice



To Tank



To Clutch



Spring



From Pump



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In this illustration, the modulating valve is shown with a maximum current signal commanded to the solenoid. When the modulation cycle stops, the Transmission/Chassis ECM sends the maximum specified current signal to fully engage the clutch. The constant current signal pushes the pin firmly against the ball in the solenoid valve. The pin force against the ball blocks more oil from flowing through the drain orifice. This restriction causes an increase in pressure on the left side of the valve spool. The valve spool moves to the right to allow pump flow to fully engage the clutch. In a short period of time, maximum pressure is felt at both ends of the proportional solenoid valve spool. This pressure along with the spring force on the right end of the spool cause the valve spool to move to the left until the forces on the right end and the left end of the valve spool are balanced. The valve spool movement to the left (balanced) position reduces the flow of oil to the engaged clutch. The Transmission/Chassis ECM sends a constant maximum specified current signal to the solenoid to maintain the desired clutch pressure.



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The different maximum specified pressures for each clutch is caused by different maximum current signals being sent by the Transmission/Chassis ECM to each individual modulating valve. The different maximum signal causes a difference in the force pushing the pin against the ball to block leakage through the drain orifice in each solenoid valve. The different rate of leakage through the spool drain orifice provides different balance positions for the proportional solenoid valve spool. Changing the valve spool position changes the flow of oil to the clutch and the resulting maximum clutch pressure. The operation of the proportional solenoid to control the engaging and releasing of clutches is not a simple on and off cycle. The Transmission/Chassis ECM varies the strength of the current signal through a programmed cycle to control movement of the valve spool. The clutch pressures can be changed using Caterpillar Electronic Technician (ET) during the calibration procedure.



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MAIN RELIEF VALVE Adjusting Screw Ball



Slug



From Pump



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The transmission hydraulic control relief valve is used to regulate the pressure to the main components in the transmission. Oil enters the relief valve at the supply port. The pressure of the oil unseats the ball and moves the spool toward the right. Oil flows past the spool and to the tank to regulate transmission oil pressure. The adjustment screw alters the preload on the spring to adjust the relief pressure.



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28 Rear Axle Check the differential oil level by removing the magnetic inspection plug (1). The oil should be level with the bottom of the fill plug opening. The magnetic inspection plug should be removed at regular intervals and checked for metal particles. The plug (2) at the bottom of the differential housing is used to drain the oil. The optional remote grease fittings (3) are located on top of the differential. Inspect the condition of the rear axle breather (4) at regular intervals. The breather prevents pressure from building up in the axle housing. Excessive pressure in the axle housing can cause brake cooling oil to leak through the Duo-Cone seals in the wheel brake assemblies. The brake cooling oil pressure can be checked at the pressure taps (5) on top of the axle. A differential carrier thrust pin is located behind the small cover (6). The thrust pin prevents movement of the differential carrier during high thrust load conditions. The backup alarm (7) is located on top of the rear frame. When the machine is in reverse, the Transmission/Chassis ECM sends a signal to sound the backup alarm.



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Shown is the differential removed from the rear axle housing. The differential is located in the rear axle housing behind the transmission. Power flows from the transmission to the differential. The differential divides the power to the right and left axle shafts. Torque is transmitted equally from the differential through the two axle shafts to the final drives. The differential adjusts the speed of the axle shafts for vehicle cornering, therefore, the power delivered to the axle shafts is unequal during cornering. The differential thrust pin contacts the differential carrier at the location shown (arrow). When high thrust loads are transmitted from the differential pinion to the differential ring gear, the carrier tries to move away from the pinion. The thrust pin prevents movement of the differential carrier during high thrust load conditions.



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TRANSMISSION/ C HASSIS CONTROL MODULE SYSTEM DIAGRAM Cat Data Link



OUTPUTS



INPUTS Key Start Switch Machine Lockout Switch Starter Lockout Switch QuickEvac Service Tool Input



Torque Converter Oil Temperature Sensor Transmission Oil Temperature Sensor



Secondary Steering Motor State Transmission Input Speed Sensor



Drive Gear Select Switches



Alternator R-Terminal



Hoist Lever Position Sensor



Transmission Charge Filter Bypass Switch Transmission Output Speed Sensor 1



Fuel Level Sender Transmission Output Speed Sensor 2 Engine Speed Sensor Head Lamp Sense



Transmission Oil Level Switch



Service Brake Accumulator Bleed Solenoid Lockup Clutch Solenoid Hoist Raise Solenoid Hoist Lower Solenoid Secondary Steering / QuickEvac / Prelube Relay



Autolube Relay



Inclinometer



Autolube Pressure Sensor



Steering System Disable Solenoid



Back-up Alarm



Location Codes



Body Up Switch



Transmission Solenoids 1-7



Primary Steering Pressure Switch



Secondary Steer Test Switch



Shift Lever Position Sensor



Start Relay



Secondary Steering Pressure Switch



Stop Lamp Relay



Secondary Brake Pressure Switch



Backup Lamp Relay



Service Brake Pressure Switch



Secondary Steering Relay



Lockup Clutch Filter Bypass Switch



Starter Lockout Lamp Machine Lockout Lamp Backlight Intensity



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Transmission/Chassis Electronic Control System Shown in this illustration are the transmission/chassis electronic control system inputs and outputs for the 777F trucks. The main purpose of the Transmission/Chassis ECM is to determine the desired transmission gear and energize the appropriate solenoids to shift the transmission up or down as required based on information from both the operator and machine. The Transmission/Chassis ECM also controls all the hoist functions, the steering disable function, and other functions as described in this presentation. The Transmission/Chassis ECM receives information from various input components such as the shift lever switch and the transmission output speed sensors. Based on the input information, the Transmission/Chassis ECM determines whether the transmission should upshift, downshift, engage the lockup clutch, or limit the transmission gear. These actions are accomplished by sending signals to various output components.



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Power train output components include the transmission modulating valve solenoids and lockup clutch solenoid. Several other Transmission/Chassis ECM output components are covered throughout the presentation. The Engine ECM, the monitoring system, the Transmission/Chassis ECM, and the Brake ECM all communicate with each other through the CAT Data Link. Communication between the electronic control modules allows the sensors of each system to be shared. Many additional benefits are provided, such as Controlled Throttle Shifting (CTS). CTS occurs when the Transmission/Chassis ECM tells the Engine ECM to reduce or increase engine fuel during a shift to lower stress to the power train. The Electronic Technician (ET) Service Tool can be used to perform several diagnostic and programming functions. NOTE: Some of the Transmission/Chassis ECM input and output components are shown during the discussion of other systems.



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The Transmission/Chassis ECM (arrow) is located in the compartment at the rear of the cab. The Transmission/Chassis ECM performs the transmission control functions, plus some other machine functions (hoist and secondary steering control). Because of the functionality of the control, it is referred to as the Transmission/Chassis ECM. The Transmission/Chassis ECM is an A4M1 module with two 70-pin connectors. The Transmission/Chassis ECM communicates with the Engine ECM, Brake ECM, and monitoring system over the CAT Data Link and can communicate with some attachments over the CAN Datalink.



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32 At the base of the shift lever (1) is a position sensor (2) which provides input signals to the Transmission/Chassis ECM when the operator moves the lever. The shift lever position sensor is a Hall-Effect position sensor. The shift lever is connected to a device which contains two magnets. One magnet (3) is visible in the bottom left view. As the lever is moved, the magnets pass over the Hall Cell (4) and the change in the magnetic field produces a signal. The internal electronics (5) of the sensor process the signal and send a PWM signal to the ECM. The lever position sensor receives 24 VDC from the machine electrical system. The sensor contains a fourth pin that is used for calibration on some machine applications. The following measurements would be typical for the position sensor with the sensor connected to the Transmission/Chassis ECM and the key switch turned ON: • Pin 1 to Pin 2 -- Supply Voltage • Pin 3 to Pin 2 -- .7 - 6.9 DCV on DC volts scale • Pin 3 to Pin 2 -- 4.5 - 5.5 KHz on the KHz scale • Pin 3 to Pin 2 -- 5% - 95% duty cycle on the % scale



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Also shown in the top right illustration is the drive gear UP switch (6) and the drive gear DOWN switch (7). The drive gear switches are toggle switches that send a signal to the Transmission/Chassis ECM. When the drive gear UP switch is pressed, the high gear limit can be increased up to seventh gear. When the drive gear DOWN switch is pressed, the high gear limit can be decreased down to third gear. The transmission shift lever lock button (8) unlocks the transmission shift lever when pressed.



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The transmission output speed sensors are located on the transfer gear housing on the input end of the transmission behind a cover (arrow). Although the sensors are physically located near the input end of the transmission, the sensors are measuring the speed of the transmission output shaft. The sensors are two wire passive sensors. The passive speed sensor uses the passing teeth of the output shaft to provide a frequency signal. The signal from the sensor is used for automatic shifting of the transmission. The signal is also used to drive the speedometer and as an input to other electronic controls. The Transmission/Chassis ECM also performs a check between the two measured transmission output speeds and the transmission input speed to ensure that the ECM calculates an accurate transmission speed. This check also uses the speeds to determine the direction of motion of the machine.



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The engine speed sensor (arrow) is located at the rear of the engine on the left side of the gear housing. The engine speed sensor sends a frequency signal to the Transmission/Chassis ECM indicating engine speed. The Transmission/Chassis ECM uses the engine speed signal input to determine actual engine speed. The actual engine speed is one of the parameters used to determine the proper transmission shift points.



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The transmission oil level switch (arrow), located near the bottom of the transmission tank, sends a signal to the Transmission/Chassis ECM indicating the hydraulic oil level in the transmission tank.



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Text Reference



1 2



36 The body up switch (1) is located on the frame near the body pivot pin. This magnetic switch is normally open. When the body is raised, a magnet (2) mounted on the body passes the switch and causes the switch to close. The resulting ground signal is sent to the Transmission/Chassis ECM. This signal is used to limit the top gear into which the transmission will shift when the body is up. The body up top gear value is programmable from FIRST to THIRD utilizing the Cat ET Service Tool. The ECM comes from the factory with this value set to FIRST gear. When driving away from a dump site, the transmission will not shift past FIRST gear until the body is down. If the transmission is already above the set limit gear when the body is raised, no limiting action will take place. The body up switch signal is also used to control the SNUB position of the hoist control valve. As the body is lowered and the magnet passes the body up switch, the Transmission/Chassis ECM signals the hoist lower solenoid to move the hoist valve spool to the SNUB position. In the SNUB position, the body float speed is reduced to prevent the body from making hard contact with the frame. The body up switch input provides the following functions: - Body up gear limiting - Body up sound reduction - Hoist snubbing - Lights the body up dash lamp - Signals a new load count (after 10 seconds in the RAISE position)



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Text Reference



A diagnostic code occurs if the Transmission/Chassis ECM does not receive a closed (ground) signal from the switch within four hours of operation time or an open signal from the switch within one hour of operation time. The body up switch must be adjusted properly for all of the functions to operate correctly. Two LEDs are located on the body up switch. The green LED indicates that battery power is present. The amber LED indicates that the switch is closed (grounded). The body position switch can be raised or lowered slightly in the bracket notches to start the SNUB feature sooner or later. NOTE: The snub feature can also be adjusted in the Cat ET hoist configuration screen by selecting the "Hoist lower valve adjustment status".



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Text Reference



TRANSMISSION/CHASSIS ECM SYSTEMS CONTROLLED BY ECM • Transmission Shifting



• Torque Converter Lockup



• Top Gear Limit



• Machine Overload Speed Limit



• Anti-hunt



• Machine Speed Limit



• Reverse Inhibitor



• Body Hoist



• Machine Lockout



• Engine Oil Pre-lubrication



• Engine Lockout



• Sound Reduction



• Neutral Start



• Backup Alarm



• Shift Counter



• Control Throttle Shifting (CTS)



• Throttle Lock



• Directional Shift Management



• Secondary Steering



• Neutral Coast Inhibiting



37



Besides controlling the Transmission Shifting and Torque Converter Lockup, the Transmission/Chassis ECM also controls other functions as shown above, such as Control Throttle Shifting (CTS), Directional Shift Management, and Top Gear Limit. There are several programmable parameters available with the Transmission/Chassis ECM. NOTE: Refer to the Transmission/Chassis Electronic Control System Operation, Troubleshooting, Testing, and Adjusting manual (RENR8342) for more information on the additional Transmission/Chassis ECM functions and programmable parameters.



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Text Reference



4 3



2



1



5



38



STEERING SYSTEM The steering system on the 777F is similar to the 777D except a steering disable solenoid valve has been added and some of the component locations have changed. When energized, the steering disable solenoid valve stops the oil flow coming from the steering pump. This prevents the front wheels from turning to allow servicing to be conducted safely in the front wheel area. The steering system uses a load sensing, pressure compensated pump. Minimal horsepower is used by the steering system when the truck is traveling in a straight path. Steering hydraulic horsepower requirements depend on the amount of steering pressure and flow required by the steering cylinders. This illustration shows the following main steering components: - Steering pump (1)



- HMU (3)



- Steering disable valve and steering valve (2)



- Steering tank (4) - Secondary steering pump (5)



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Text Reference



39



1



3



4



2



40



3



The steering system tank is located on the right platform Check the steering system oil level at the sight gauge (1). The steering system oil filter (2) is located on the side of the steering tank. The steering system uses a pressure compensated piston type pump. Case drain oil from the steering pump returns to the hydraulic tank through a case drain filter (3) on the side of the steering tank. Before removing the cap to add oil to the steering system, depress the pressure release button (4) on the breather to release any remaining pressure from the tank.



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Text Reference



The steering system filter base and the case drain filter base have bypass valves that allow the steering oil to bypass the filters if they are plugged.



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Text Reference



2 1



41



The 777F Trucks are equipped with a load sensing, pressure compensated, piston-type pump. The steering pump operates only when the engine is running and provides the necessary flow of oil for steering system operation. The steering pump contains a load sensing controller with two valves. The high pressure cutoff valve (1) functions as the primary steering system relief valve. The flow compensator valve (2) is used to adjust the low pressure standby setting. When the truck is traveling in a straight path, virtually no flow or pressure is sent to the steering cylinders, and the pump destrokes to low pressure standby.



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Load Sensing Pressure from HMU



To Steering Valve and HMU



Text Reference



STEERING PUMP



LOW PRESSURE STANDBY



High Pressure Cutoff Valve



Actuator Piston



Flow Compensator Load Sensing Controller



Case Drain Filter



Swashplate Piston



42



When the truck is traveling in a straight path, the steering cylinders require virtually no flow or pressure. The HMU provides a very low pressure load sensing signal to the flow compensator in the load sensing controller. Pump oil (at low pressure standby) flows to the swashplate piston and past the lower end of the displaced flow compensator spool to the actuator piston. The actuator piston has a larger surface area than the swashplate piston. The oil pressure at the actuator piston overcomes the spring force and the oil pressure in the swashplate piston and moves the swashplate to destroke the pump. The pump is then at minimum flow, low pressure standby. Pump output pressure is equal to the setting of the flow compensator plus the pressure required to compensate for system leakage.



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Load Sensing Pressure from HMU



Text Reference



STEERING PUMP



To Steering Valve and HMU



MAXIMUM FLOW



High Pressure Cutoff Valve



Actuator Piston



Flow Compensator Load Sensing Controller Swashplate Piston Case Drain Filter



43



During a turn, when steering pressure and flow are required, pressure increases in the HMU load sensing signal line. The pressure in the signal line is equal to the pressure in the steering cylinders. The pump load sensing controller is spring biased to vent the actuator piston pressure to drain. Venting pressure from the load sensing controller and the actuator piston positions the spring biased swashplate to maximum displacement (maximum flow). As pressure increases in the HMU load sensing signal line, pump supply pressure is sensed on both ends of the flow compensator. When pressure is present on both ends of the flow compensator, the swashplate is kept at maximum angle by the force of the spring in the pump housing and pump discharge pressure on the swashplate piston. The pistons reciprocate in and out of the barrel and maximum flow is provided through the outlet port. Since the pump is driven by the engine, engine rpm also affects pump output.



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Text Reference



44 1



45 2 3



4



The steering disable valve (1) is located behind the shock on the right frame rail. When the steering disable solenoid valve (2) is energized, oil flow from the steering pump to the steering valve is blocked by the steering disable valve, which allows servicing behind the front wheels with the machine running. When the machine lockout switch, located under a panel on the left stairway, is toggled, a signal is sent to the Transmission/Chassis ECM. The Transmission/Chassis ECM energizes the steering disable solenoid allowing service to be performed behind the front wheels safely. Also located on the steering disable valve is a pressure tap (3) for checking the load sensing signal to the pump, and an S•O•S tap (4).



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2



5



Text Reference



1 3 46



6 7



4



47



2



Steering oil flows from the pump through the steering disable valve to the steering valve (1) located on the frame behind the right front suspension cylinder. The primary steering pressure switch (2) monitors the output of the steering pump. The steering pressure switch provides input signals to the Transmission/Chassis ECM which sends a signal to the monitoring system to inform the operator of the steering system condition. A steering system warning is displayed if the pressure is too low. The steering pressure switch cannot tolerate high steering system pressures. A pressure reducing valve (not visible) reduces the steering system pressure to the steering pressure switch.



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Text Reference



Two relief valves are located on the left side of the steering valve. The top relief valve (3) is a back-up relief valve for the secondary steering system. The secondary steering back-up relief valve protects the secondary steering system if the relief valve on the secondary steering pump malfunctions. The lower relief valve (4) is a back-up relief valve for the primary steering system. The primary steering back-up relief valve protects the primary steering system if the high pressure cutoff valve on the steering pump malfunctions. Primary steering pressure is first controlled by the high pressure cutoff valve located on the steering pump. Check valves are used to separate the primary and secondary steering systems. The secondary check valve (5) is behind the left plug, and the primary check valve (6) is behind the right plug. Steering system pressures can be measured at the steering system pressure tap (7).



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Text Reference



48



This illustration shows the location of the HMU (arrow) for the 777F. Serviceability has improved for the HMU on the 777F due to the redesigned walkways. The HMU is connected to the steering wheel and controlled by the operator. The HMU meters the amount of oil sent to the steering cylinders by the speed at which the steering wheel is turned. The faster the HMU is turned, the higher the flow sent to the steering cylinders, and the faster the wheels will change direction. The steering system is referred to as "Q-amp" which means flow amplification. During a sudden steering change (steering wheel speed greater than 10 rpm), additional steering pump oil flow will bypass the gerotor pump in the HMU and flow directly to the steering cylinders. Steering oil flow to the cylinders is equal to the gerotor pump oil flow plus the bypass oil flow from the steering pump. The steering oil flow is amplified up to 1.6 to 1. The purpose of the flow amplification is to provide quick steering response when sudden steering changes are needed. Two crossover relief valves are installed in the top of the HMU. The crossover relief valves are installed in series with the left and right turn ports. If an outside force is applied to the front wheels while the steering wheel is stationary, the crossover relief valves provide circuit protection for the steering lines between the steering cylinders and the HMU. The crossover relief valves allow oil to transfer from one end of the steering cylinders to the opposite end of the cylinders.



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Text Reference



To test the right crossover relief valve, install two tees with pressure taps in the right turn steering hose at the steering cylinders. Steer the truck completely to the right against the stops, and shut off the engine. An external pump supply must be connected to one of the pressure taps on the right turn hose. Connect a pressure gauge to the other pressure tap on the right turn hose. Pressurize the steering system, and the reading on the gauge will be the setting of the right crossover relief valve. To test the left crossover relief valve, install two tees with pressure taps in the left turn steering hose at the steering cylinders. Steer the truck completely to the left against the stops, and shut off the engine. An external pump supply must be connected to one of the pressure taps on the left turn hose. Connect a pressure gauge to the other pressure tap on the left turn hose. Pressurize the steering system, and the reading on the gauge will be the setting of the left crossover relief valve.



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Text Reference



49 2



3



1



4



2



5



4 6 50



3



1



The electric secondary steering pump (1) and motor (2) on the 777F are the same as the 777D, however the location has changed. The pump and motor are now located on the front of the front crossmember. The pump and motor assembly also includes the brake release pump section (3) and the prelubrication (QuickEvac) pump section (4). The secondary pressure switch (5) is also mounted next to the secondary steering pump. The pressure switch detects if the wheels are being turned via the steering wheel when secondary steering is activated. When the wheel is turned in a secondary steering condition, the pressure switch will signal the Transmission/Chassis ECM and the QuickEvac function will be disabled.



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Text Reference



If the primary steering pressure switch signals the Transmission/Chassis ECM that the steering system pressure is low, the ECM will energize the secondary steering relay located behind the cab. The secondary steering relay will then energize a second larger relay located on the frame above the steering valve, which will then energize the secondary steering motor. The primary relief valve for the secondary steering is accessible through the small allen head plug (6). To check the setting of the secondary steering primary relief valve, do not start the truck. Turn ON the key start switch and depress the secondary steering switch in the cab. Turn the steering wheel hard to the left or right while the secondary steering pump is running. Secondary steering system pressures can be measured at the steering system pressure tap.



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Text Reference



Crossover Relief Valves



STEERING HYDRAULIC SYSTEM HMU



Primary Steering Back-up Relief Valve Pressure Reducing Valve Load Sensing Valve Secondary Pressure Switch



Primary Steering Pressure Switch Secondary Steering Back-up Relief Valve Transmission Chassis ECM



Steering Valve



Piston Pump and Load Sensing Controller



M



Secondary Steering Primary Relief Valve



Secondary Steering Pump Flow Compensator



Steering Disable Valve



Actuator Piston



Steering Filter



Swashplate Piston



Case Drain Filter



51



Shown is a schematic of the steering hydraulic system in the HOLD position. The primary steering pump pulls oil from the steering tank. All piston-type pumps produce a small amount of leakage to the case drain circuit for lubrication and cooling. The case drain oil flows to the steering tank through a case drain filter. Steering oil flows from the pump to the steering disable valve. When the steering disable valve is energized, oil is allowed to flow to the steering valve. In the steering valve, a steering pressure switch monitors the output of the steering pump. The steering pressure switch cannot tolerate high steering system pressures. A pressure reducing valve lowers the steering system pressure to the steering pressure switch. If the steering pressure switch signals the Transmission/Chassis ECM that the steering system pressure is low, the ECM will then energize the secondary steering motor. Secondary steering supply oil will flow to the steering valve.



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Text Reference



Two relief valves are installed in the steering valve. The secondary steering back-up relief valve protects the secondary steering system if the relief valve on the secondary steering pump malfunctions. The primary steering back-up relief valve protects the primary steering system if the high pressure cutoff valve on the steering pump malfunctions. Two check valves are located on the steering valve. The check valves are used to separate the primary and secondary steering systems. Steering supply oil flows to the HMU from the steering valve. Return oil from the HMU flows through the steering valve and the steering filter to the steering tank. The HMU meters the amount of oil sent to the steering cylinders by the speed at which the steering wheel is turned. The faster the HMU is turned, the higher the flow sent to the steering cylinders, and the faster the wheels will change direction. Two crossover relief valves are installed in the top of the HMU. The crossover relief valves are installed in series with the left and right turn ports. If an outside force is applied to the front wheels while the steering wheel is stationary, the crossover relief valves provide circuit protection for the steering lines between the steering cylinders and the HMU. The crossover relief valves allow oil to transfer from one end of the steering cylinders to the opposite end of the cylinders. When the Transmission/Chassis ECM energizes the secondary steering motor, load sensing signal oil will flow from the secondary steering load sensing valve through the load sensing resolver to the HMU. The load sensing valve uses the load sensing signal pressure to control the amount of flow from the secondary steering pump to the steering valve. The 777F Trucks use a dynamic load sensing steering system the same as the late model "D Series" Trucks. In a dynamic system, there is load sensing pressure and flow between the HMU and the steering pumps. A load sensing pilot signal resolver valve is located in the steering disable valve. The resolver valve allows load sensing signal oil to flow between the HMU and the primary steering pump or the secondary steering pump. In the NO STEER position, oil flows to the HMU. In a LEFT or RIGHT STEER position, oil also flows from the HMU to the resolver valve. Normally, the secondary steering pump is OFF and the resolver is closed from the HMU to the secondary steering pump. The flow from the primary steering pump holds the resolver open and load sensing pilot signal pressure is present between the HMU and the piston pump flow compensator. The load sensing signal flow from the primary steering pump is also used for "thermal bleed" through the HMU. The "thermal bleed" is used to keep the HMU temperature the same as the rest of the steering system. Keeping the HMU the same temperature prevents sticking.



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Text Reference



4 3 1



2 3



52



HOIST SYSTEM The hoist system on the 777F Update trucks is electronically controlled by the Transmission/Chassis ECM. The hoist control system operates similar to the 777D trucks. The main components in the hoist system are: - Hoist control lever and position sensor (in cab) - Hoist pump (1) - Hoist control valve (2) - Hoist cylinders (3) - Hydraulic oil tank (4)



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Text Reference



53



The operator controls the hoist lever (arrow). The four positions of the hoist lever are RAISE, HOLD, FLOAT and LOWER. The hoist valve has a fifth position referred to as the SNUB position. The operator is unaware of the SNUB position because a corresponding lever position is not provided. When the body is being lowered, just before the body contacts the frame, the Transmission/Chassis ECM signals the hoist lower solenoid to move the hoist valve spool to the SNUB position. In the SNUB position, the body float speed is reduced to prevent the body from making hard contact with the frame. The hoist system can be enabled or disabled using ET. All trucks shipped from the factory without bodies installed are set at the Hoist Enable Status 2. The Hoist Enable Status 2 is a test mode only and will prevent the hoist cylinders from accidentally being activated. After the body is installed, change the Hoist Enable Status to 1 for the hoist system to function properly. The truck should normally be operated with the hoist lever in the FLOAT position. Traveling with the hoist in the FLOAT position will make sure the weight of the body is on the frame and body pads and not on the hoist cylinders. The hoist control valve will actually be in the SNUB position. If the transmission is in REVERSE when the body is being raised, the hoist lever sensor is used to shift the transmission to NEUTRAL. The transmission will remain in NEUTRAL until the hoist lever is moved into the HOLD or FLOAT position and the shift lever has been cycled into and out of NEUTRAL. NOTE: If the truck is started with the body raised and the hoist lever in FLOAT, the lever must be moved into HOLD and then FLOAT before the body will lower.



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Text Reference



1



3



2



54



The hoist lever (1) controls a position sensor (2). The PWM sensor sends duty cycle input signals to the Transmission/Chassis ECM. The hoist lever position sensor is a Hall-Effect position sensor and operates the same as the transmission shift lever sensor (3) previously described. Depending on the position of the sensor and the corresponding duty cycle, one of the two solenoids located on the hoist valve is energized. The four positions of the hoist lever are RAISE, HOLD, FLOAT, and LOWER, but since the sensor provides a duty cycle signal that changes for all positions of the hoist lever, the operator can modulate the speed of the hoist cylinders. The hoist lever sensor performs three functions: - Raises and lowers the body - Neutralizes the transmission in REVERSE - Starts a new TPMS cycle



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Text Reference



3



1 2



55



Shown is the hoist, converter, and brake hydraulic tank. The oil level is checked by opening the small door (1) and looking at the sight gauge. The oil level should first be checked with cold oil and the engine stopped. The level should again be checked with warm oil and the engine running. The lower sight gauge (2) can be used to fill the tank when the hoist cylinders are in the RAISED position. When the hoist cylinders are lowered, the hydraulic oil level will increase. After the hoist cylinders are lowered, check the hydraulic tank oil level with the upper sight gauge as explained above. Check the hoist, converter, and brake hydraulic tank breather (3) for restriction. Clean the filter if it is restricted.



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Text Reference



3



2 4 5 6



1



7



8



56



Shown is the rear of the hoist, converter, and brake hydraulic tank. The hoist pump pulls oil from the tank through the suction screen (1) located in the rear of the tank. Oil returns from the hoist valve through the port (2). Brake cooling oil returns to the hydraulic tank through the three upper ports (3). Other ports located on the hydraulic tank are: - Transmission charging pump suction (4) - Transmission return (5) - Torque converter pump suction (6) - Brake cooling pump suction (7) - Torque converter inlet relief valve return (8)



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Text Reference



57 1



1



58 2



The hoist pump (1) is a gear type pump that is attached to the drive gear at the rear of the engine. Mounted to the hoist pump is the brake cooling pump and the brake charging pump. Oil flows from the hoist pump to the hoist control valve. The hoist system relief pressures are different in the RAISE and LOWER positions. The body up switch must be in the RAISE position before the LOWER relief valve setting can be tested. Move a magnet past the body up switch until the body up alert indicator on the dash turns ON. If the body up switch is in the LOWER position, the Transmission/Chassis ECM will hold the hoist valve in the SNUB position and the LOWER relief valve will not open.



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Text Reference



In the HOLD, FLOAT and SNUB positions, the gauge will show the brake cooling system pressure, which is a result of the restriction in the coolers, brakes and hoses (normally much lower than the actual oil cooler relief valve setting). The maximum pressure is limited by the oil cooler relief valve. Hoist pump pressure can be checked at the pressure tap (2) on the pump.



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Text Reference



2 2



1



59



The hoist control valve (1) is located behind the engine on the right side of the frame. The hoist valve is the same as the hoist control valve on the 777D. The hoist valve uses torque converter lockup clutch pump oil as the pilot oil to shift the directional spool inside the hoist valve. Lockup clutch pump oil enters the hydraulic actuators (2) on both ends of the hoist valve.



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Text Reference



7 6 1



2



3



4



5



60



Pilot oil pressure is always present at both ends of the directional spool. Two solenoid valves are used to drain the pilot oil from the ends of the directional spool, which then allows the spool to move. The solenoid on the right is the RAISE solenoid valve (1), and the solenoid on the left is the LOWER solenoid valve (2). The left pressure tap (3) is used to check the pilot pressure of the hoist lower solenoid. The right pressure tap (4) is used to check the pilot pressure of the raise solenoid. When the Transmission/Chassis ECM receives an input signal from the hoist lever sensor, the ECM sends an output signal current between 0 and 1.9 amps to one of the solenoids. The amount of current sent to the solenoid determines how much pilot oil is drained from the end of the directional spool and, therefore, how far the directional spool travels toward the solenoid. An oil cooler relief valve is located in the hoist control valve behind the large plug (5). The relief valve limits the brake oil cooling pressure when the hoist valve is in the HOLD, FLOAT or SNUB position. The hoist system relief pressures are controlled by the two relief valves located on top of the hoist valve. The RAISE relief valve (6) limits the pressure in the hoist system during RAISE. The LOWER relief valve (7) limits the pressure in the hoist system during LOWER. NOTE: The hoist valve LOWER position (snub adjustment) is an adjustable parameter in the Transmission/Chassis ECM using Cat ET. The slight adjustment provides a means to compensate for valve differences. This is the snub adjustment.



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Text Reference



1 2



61



The hoist cylinder lower circuit pressure tap (1) and raise circuit pressure tap (2) are located on the cross-tube between the lower hoist cylinder mounts. The relief valve pressure setting is tested with the engine at HIGH IDLE and the hoist valve in the RAISE or LOWER position. The body up switch at the frame near the body pivot pin must be in the RAISE position before the LOWER relief valve setting can be tested. Move a magnet past the body up switch until the body up alert indicator on the dash turns ON. If the body up switch is in the LOWER position, the Transmission/Chassis ECM will hold the hoist valve in the SNUB position and the LOWER relief valve will not open. An orifice plate is installed between the upper hose and the rod end port on both hoist cylinders. The orifice plate restricts the flow of oil from the rod end of the hoist cylinders. The orifice plate also prevents cavitation of the cylinders when the body raises faster than the pump can supply oil to the cylinders (caused by a sudden shift of the load). NOTE: If the snub feature is not adjusted correctly, residual pressure will exist in the head side of the cylinders and the body will not rest on the frame. The raise circuit pressure tap should be used to ensure there is no residual pressure in the head side of the cylinders. Otherwise, when checking the raise (high) circuit pressure, the pressure tap on the hoist pump is easier to access.



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Text Reference



Raise Solenoid



Brake Cooling Relief Valve



Parking Brake Release Pressure



Low Pressure Relief Valve



Main Relief Dump Valve



To Brake Cooling



High Pressure Relief Valve To Hoist Cylinder Rod End



Dual Stage Relief Valve Signal Stem



To Hoist Cylinder Head End



Load Check Valve



HOIST CONTROL VALVE HOLD



Parking Brake Release Pressure Lower Solenoid



62



This illustration shows a sectional view of the hoist control valve in the HOLD position. Pilot oil pressure is present at both ends of the directional spool. The spool is held in the centered position by the centering springs and the pilot oil. Passages in the directional spool vent the dual stage relief valve signal stem to the tank. All the hoist pump oil flows through the brake oil coolers to the rear brakes. The position of the directional spool blocks the oil in the head end and rod end of the hoist cylinders. A gauge connected to a pressure tap at the pump while the hoist valve is in the HOLD position will show the brake cooling system pressure, which is a result of the restriction in the coolers, brakes and hoses. The maximum pressure in the circuit should correspond to the setting of the brake oil cooler relief valve.



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Text Reference



ON Raise Solenoid



Brake Cooling Relief Valve



Parking Brake Release Pressure



Low Pressure Relief Valve



Main Relief Dump Valve



To Brake Cooling



High Pressure Relief Valve From Hoist Cylinder Rod End



Dual Stage Relief Valve Signal Stem



To Hoist Cylinder Head End



Load Check Valve



HOIST CONTROL VALVE RAISE



Parking Brake Release Pressure Lower Solenoid



63



In the RAISE position, the raise solenoid is ENERGIZED and drains pilot oil from the upper end of the directional spool. The directional spool moves up. Pump oil flows past the load check valve and the directional spool to the head end of the hoist cylinders. When the directional spool is initially shifted, the load check valve remains closed until the supply pressure is higher than the pressure in the hoist cylinders. The load check valve prevents the body from dropping before the RAISE pressure increases. The directional spool also sends hoist cylinder raise pressure to the dual stage relief valve signal stem. The dual stage relief valve signal stem moves down and blocks the supply pressure from opening the low pressure relief valve. Oil flowing from the rod end of the hoist cylinders flows freely through the brake oil cooler to the brakes. If the pressure in the head end of the hoist cylinders exceeds the relief valve settings, the high pressure relief valve will open. When the high pressure relief valve opens, the dump valve moves to the left and pump oil flows to the tank.



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Text Reference



The high pressure hoist relief valve setting is checked at the hoist pump pressure tap or the head end pressure tap. Check the relief pressure with the hoist lever in the RAISE position and the engine at HIGH IDLE.



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Text Reference



Raise Solenoid



Brake Cooling Relief Valve



Parking Brake Release Pressure



Low Pressure Relief Valve



Main Relief Dump Valve



To Brake Cooling



High Pressure Relief Valve To Hoist Cylinder Rod End



Dual Stage Relief Valve Signal Stem



From Hoist Cylinder Head End



Load Check Valve



HOIST CONTROL VALVE LOWER/POWER DOWN



Parking Brake Release Pressure Lower Solenoid



ON



64



In the LOWER (power down) position, the LOWER solenoid is energized and drains pilot oil from the lower end of the directional spool. The directional spool moves down. Supply oil from the pump flows past the load check valve and the directional spool to the rod end of the hoist cylinders. Oil in the head end of the hoist cylinders flows to the tank through holes in the directional spool. The supply oil in the rod end of the cylinders and the weight of the body move the cylinders to their retracted positions. Just before the body contacts the frame, the body up switch sends a signal to the Transmission/Chassis ECM to move the directional spool to the SNUB position. In the SNUB position, the directional spool moves slightly to restrict the flow of head end oil through only some of the holes in the spool which allows the body to lower gradually. The directional spool also vents the passage to the dual stage relief valve signal stem. The dual stage relief valve signal stem allows supply pressure to be limited by the low pressure relief valve. If the pressure in the rod end of the hoist cylinders is too high, the low pressure relief valve will open. When the low pressure relief valve opens, the dump valve moves to the left and pump oil flows to the tank.



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Text Reference



The low pressure hoist relief valve setting is checked at the rod end pressure tap. Check the relief pressures with the hoist lever in the LOWER position and the engine at HIGH IDLE. The body up switch must be in the RAISE position before the LOWER relief valve setting can be tested. Move a magnet past the body up switch until the body up alert indicator on the dash turns ON. If the body up switch is in the LOWER position, the Transmission/Chassis ECM will hold the hoist valve in the SNUB position and the LOWER relief valve will not open.



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Text Reference



Raise Solenoid Low Pressure Relief Valve



Brake Cooling Relief Valve



Parking Brake Release Pressure



Main Relief Dump Valve



To Brake Cooling



High Pressure Relief Valve To Hoist Cylinder Rod End



Dual Stage Relief Valve Signal Stem



From Hoist Cylinder Head End



Load Check Valve



HOIST CONTROL VALVE FLOAT



Parking Brake Release Pressure Lower Solenoid



ON



65



In the FLOAT position, the LOWER solenoid is partially energized and drains some of the pilot oil at the lower end of the directional spool to the tank. The directional spool moves down. Because the pilot oil is only partially drained, the directional spool does not move down as far as during LOWER (power down). Pump supply oil flows past the load check valve and the directional spool to the rod end of the hoist cylinders. Oil in the head end of the hoist cylinders flows to the tank. The position of the directional spool permits the pressure of the oil flowing to the brake oil cooler to be felt at the rod end of the hoist cylinders. The truck should normally be operated with the hoist lever in the FLOAT position. Traveling with the hoist in the FLOAT position will make sure the weight of the body is on the frame and body pads and not on the hoist cylinders. The hoist valve will actually be in the SNUB position.



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Text Reference



Raise Solenoid Low Pressure Relief Valve



Brake Cooling Relief Valve



Parking Brake Release Pressure



Main Relief Dump Valve



To Brake Cooling



High Pressure Relief Valve To Hoist Cylinder Rod End



Dual Stage Relief Valve Signal Stem



From Hoist Cylinder Head End



Load Check Valve



HOIST CONTROL VALVE SNUB



Parking Brake Release Pressure Lower Solenoid



ON



66



In the SNUB position as the body is lowered, just before the body contacts the frame, the body up switch sends a signal to the Transmission/Chassis ECM to move the directional spool to the SNUB position. In the SNUB position, the directional spool moves slightly to a position between HOLD and FLOAT. The SNUB position restricts the flow of oil and lowers the body gradually. The operator does not control the SNUB position. When the hoist lever is in the LOWER or FLOAT position and the body up switch is in the DOWN position, the hoist control valve is in the SNUB position. A gauge connected to the rod end pressure tap while the hoist control valve is in the SNUB position will show the brake cooling system pressure, which is a result of the restriction in the coolers, brakes and hoses. The maximum pressure in the circuit should correspond to the setting of the brake oil cooler relief valve.



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Text Reference



2



1



67



Two-stage hoist cylinders (1) are used to raise the body. Oil flows from the hoist control valve to the two hoist cylinders when the directional spool in the hoist control valve is not in HOLD. Check the condition of the body pads (2) for wear or damage. Hoist pilot pressure is required to lower the body with a dead engine. The towing pump can be used to provide the hoist pilot oil.



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Text Reference



Left Front



777F HOIST AND BRAKE COOLING SCHEMATICS



Right Front



From Torque Converter Lockup Clutch Pilot Main Relief Dump Spool



From Tow Pump Circuit



Left Rear



From Torque Converter From Torque Lockup Clutch Converter Pump



Lower / Float / Snub Solenoid From Brake System



RAISE



Right Rear



SNUB Brake Cooling Pressure Test Port



Cylinder Rod End Pressure Test Port



FLOAT



Brake Cooling Relief



LOWER



68



This illustration shows the hoist hydraulic system in the HOLD position. The hoist pump pulls oil from the hydraulic tank through the suction screen located in the rear of the tank. Oil flows from the hoist pump to the hoist control valve. When the hoist control valve is in the HOLD, FLOAT or SNUB position, all the hoist pump oil flows through the brake oil coolers located on the right side of the engine. Oil flows from the oil coolers, through the brakes, and returns to the hydraulic tank. NOTE: If the truck is equipped with the optional caliper type front brake system, the brake cooling pump is not installed and oil from the hoist pump will flow to only the rear brakes. A brake cooling relief valve is located in the hoist control valve. The relief valve limits the brake oil cooling pressure when the hoist control valve is in the HOLD, FLOAT or SNUB position. The hoist valve uses torque converter lockup clutch pump oil as the pilot oil to shift the directional spool inside the hoist control valve. Oil flows from the lockup clutch pump to both ends of the hoist control valve.



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Text Reference



Pilot pressure is always present at both ends of the directional spool. Two solenoid valves are used to drain the pilot oil from the ends of the directional spool, which then allows the centering springs and the pressure on the opposite end of the spool to move the spool. When the RAISE solenoid is energized, the directional spool will move toward the RAISE solenoid. The RAISE and LOWER solenoid valves constantly receive approximately 300 millivolts at a frequency of 80 Hz from the Transmission/Chassis ECM when they are in any position except HOLD. The excitation, referred to as "dither," is used to keep the solenoids in a ready state for quick response. When the Transmission/Chassis ECM receives an input signal from the hoist lever sensor, the ECM sends an output signal current between 0 and 1.9 amps to one of the solenoids. The amount of current sent to the solenoid determines how much pilot oil is drained from the end of the directional spool and, therefore, the distance that the directional spool travels. The truck should normally be operated with the hoist lever in the FLOAT position. Traveling with the hoist in the FLOAT position will make sure the weight of the body is on the frame and body pads and not on the hoist cylinders. The hoist valve will actually be in the SNUB position. When the hoist control valve is in the RAISE position, pump supply oil flows to the head end of the hoist cylinders. Pump supply oil also flows to the dual stage signal spool and moves the spool to the left. When the dual stage signal spool moves to the left, pump supply oil is blocked from the LOWER relief valve, and the RAISE relief valve will limit the hoist system pressure. When the hoist control valve is in the LOWER (power down), FLOAT or SNUB position, pump supply oil flows to the rod end of the hoist cylinders. Pump supply oil is blocked from the dual stage signal spool and the spring holds the spool in the right position. When the dual stage signal spool is in the right position, pump supply oil can flow to the LOWER relief valve, and hoist system pressure is controlled by the LOWER relief valve. An orifice plate is installed between the upper hose and the rod end port on both hoist cylinders. The orifice plate prevents cavitation of the cylinders when the body raises faster than the pump can supply oil to the cylinders (caused by a sudden shift of the load).



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3



1



9



Text Reference



4



5



6



2



8



7



69 BRAKE SYSTEM Two separate brake systems are used on the 777F. The two brake systems are the service/retarder brake system and the parking/secondary brake system. The parking/secondary brakes are spring engaged and hydraulically released. The service/retarder brakes are hydraulically engaged and spring released. The braking system is also equipped with a Brake ECM that controls the braking system functions, including the Automatic Retarder Control (ARC) and the Traction Control System (TCS). The air system on the previous model trucks has been completely removed. The main components in the braking system are: - Brake charging pump (1)



- Cab brake manifold (5)



- Brake cooling pump (standard oil cooled front brakes) (2)



- Service brake valve (6)



- Accumulator charging valve (3) - Brake accumulators (4)



- Brake oil filter (7) - Front slack adjuster (8) - Brake accumulator check valve (9)



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Text Reference



70



The rear brakes on the 777F Trucks are oil cooled. Shown is a cutaway illustration of an oil cooled brake assembly. The brakes are environmentally sealed and adjustment free. Oil continually flows through the brake discs for cooling. Duo-Cone seals prevent the cooling oil from leaking to the ground or transferring into the axle housing. The wheel bearing adjustment must be maintained to keep the Duo-Cone seals from leaking. The smaller piston (yellow) is used to engage the secondary and parking brakes. The parking brakes are spring engaged and hydraulically released. The larger piston (purple) is used to engage the service and retarder brakes. The service and retarder brakes are engaged hydraulically and released by spring force.



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Text Reference



Brake Actuation Pressure



777F STANDARD FRONT BRAKE



Disassembly Service Plug



71



The standard oil cooled front brakes are also environmentally sealed and adjustment free. The piston (yellow) is used to ENGAGE the service/retarder brakes. The front brakes do not have a second piston for the parking/secondary brakes. When the wheel is removed for service, the small plug at the lower left must be removed (the brake assembly is equipped with two similar plugs). Two 3/8 inch bolts must be installed at the plug locations to hold the brake discs and plates in position during wheel removal. The bolts ensure proper alignment of the teeth on the discs and plates during installation.



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Text Reference



777F OPTIONAL CALIPER DISC BRAKE Piston Bleed Valve Caliper



Carrier Lining



From Brake Cylinder



Disc



72



With the optional disc and caliper design brakes, the brake caliper assemblies are fastened to the spindle and do not rotate. The brake disc is fastened to the wheel and rotates with the wheel. Air can be bled from the front brakes through the bleed valves. During brake application, hydraulic oil from the brake cylinders forces the brake pistons against the brake carrier linings (brake pads). The brake linings are forced against the disc to stop the rotation of the wheel.



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Text Reference



3



2



1



73



3 2 1



74



The brake charging pump (1), the brake oil cooling pump (2), and the hoist pump (3) are mounted to the pump drive gear on the left rear side of the engine. The 777F brake system accumulators are charged by the brake charging pump, which supplies oil to the accumulator charging valve. The oil cooling pump sends oil to the oil coolers before the oil flows to the front and rear brakes for brake cooling. NOTE: The brake oil cooling pump is not installed on trucks with the optional caliper type front brakes.



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Text Reference



2



1



75



The brake system filter (1) is located on the left outer rear frame next to the left rear strut mount. The brake filter includes a filter bypass switch (2), which sends a signal to the Brake ECM if the filter is restricted. The Brake ECM sends a signal to the monitoring system, which illuminates the brake system-check indicator lamp.



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Text Reference



2



5 76 3



1



4



77 1



The accumulator charging valve (1) is located on the left side of the frame near the brake accumulators. The accumulator charging valve directs oil to the brake accumulators, brake oil coolers, and the tank. Once the accumulators are charged, the excess oil flow is sent to cool the brakes before returning to the tank. The Brake ECM monitors the pressure in the service brake accumulators with the brake accumulator pressure switch (2). If the pressure in the service brake accumulators is low, the Brake ECM will signal the monitoring system to turn on the brake system-check indicator lamp. A relief (3) valve limits the pressure in the brake charging circuit. A pressure tap (4) on the line between the brake charging pump and the accumulator charging valve is used to check the charge oil pressure from the pump. The pressure tap (5) on the charging valve is used to check the oil pressure in the service brake accumulators.



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Text Reference



ACCUMULATOR CHARGING VALVE To Brake Accumulators



CUT-IN



Accumulator Oil Pressure Switch



Cut-In / Cut-Out Spool



Relief Valve



Unloading Valve



To Brake Cooling System



From Brake Charging Pump



78



The accumulator charging valve maintains the pressure in the accumulators at a constant rate while the engine is running. If the machine has lost power or the hydraulic pump has failed, the pressure in the accumulators will permit several applications of the service brakes. This illustration shows the accumulator charging valve in the CUT-IN position. When the accumulator oil pressure decreases below a certain point, the accumulator charging valve reaches the cut-in pressure setting. The pressure decrease allows spring force to move the cut-in/cut-out spool to the left and oil flows to the right end of the unloading valve. The orifice in the unloading valve restricts the pump flow to the brake cooling system. Oil flow to the brake accumulators increases and the accumulators are charged. The accumulator oil pressure switch sends a signal to the Brake ECM to alert the operator when the brake oil pressure drops below the minimum operating pressure.



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Text Reference



ACCUMULATOR CHARGING VALVE CUT-OUT To Brake Accumulators



Accumulator Oil Pressure Switch



Cut-In / Cut-Out Spool



Relief Valve



Unloading Valve



To Brake Cooling System



From Brake Charging Pump



79



This illustration shows the accumulator charging valve in the CUT-OUT position. When the accumulator oil pressure increases to the cut-out pressure setting, the increased pressure causes the cut-in/cut-out spool to move right against spring force. Oil at the right end of the unloading valve flows to the tank. Oil pressure on the left end of the unloading spool overcomes the decreased oil pressure on the right end of the spool and spring force. Most of the brake charging pump oil now flows to the brake cooling system. The check valve prevents high accumulator oil pressure from flowing to the brake cooling system. The accumulator charging valve remains in the CUT-OUT position until the pressure in the accumulators decreases to the cut-in pressure setting. The pressure relief valve regulates the oil pressure in the brake circuit. Any excess oil that is not required by the brake cooling system or the brake circuit is diverted back to the hydraulic oil tank.



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Text Reference



80



1



1 2



81 1



1 2



There are the three brake accumulators for the 777F located on the left side of the frame. The service brake accumulators (1) and parking brake accumulator (2) are charged by the brake charging pump and supply the required oil flow to engage the front and rear service brakes and release the rear parking brakes. A check valve in the circuit between the parking brake accumulator and the service brake accumulators allows only the parking brake accumulator to be charged when using the electric brake release pump.



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3



Text Reference



2 82



1



4 83



1



3



2



The cab brake manifold (1) is mounted below the cab on the left upper frame. The cab brake manifold contains the ARC control solenoid (2) and the front service brake solenoid (3). The ARC control solenoid is part of the ARC system. The ARC system uses the rear service brakes and the front oil cooled brakes to automatically control the speed of the truck. The service brake pressure switch (4) is located near the cab brake manifold toward the front of the machine. The service brake pressure switch sends a signal to the Brake ECM when the service brakes are engaged. The Brake ECM will use the signal from the pressure switch to energize the stop lamp relay (located in cab) and turn on the brake lights. In a low pressure situation, the Brake ECM will signal the monitoring system to activate the brake system-check indicator.



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Text Reference



2 84 3



85



1



The service brake valve (1) is mounted below the floor of the operator’s cab. When the service brake pedal (2) is depressed, an internal spool directs oil flow from the service brake accumulators to the rear service brakes. The amount of oil flow to the front service brakes is determined by the Brake ECM based on a signal from the service brake pedal position sensor (3). The Brake ECM allows some oil from the brake accumulators to flow to the front brakes by controlling the position of the front brake solenoid located in the cab brake manifold. NOTE: If the front brake switch (optional front caliper type brakes only) is activated, the Brake ECM will command all oil to flow to the rear brakes.



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Text Reference



2



3



4 1



86



When the manual retarder lever (1) is activated, a PWM signal is sent to the Brake ECM. The Brake ECM sends a signal to the ARC solenoid and the front brake solenoid. The solenoids control the amount of oil flow to the service brakes based on the position of the retarder lever. If the ARC switch (2) is activated, the Brake ECM sends a signal to the ARC solenoid and the front brake solenoid. The solenoids control the amount of oil flow to the service brakes based upon the input signals that the Brake ECM receives from the engine speed sensor. NOTE: If the truck is equipped with the optional front caliper type brakes, the Brake ECM will command all oil to flow to the rear brakes when the retarder lever is moved or the ARC switch is activated. The optional engine brake switch (3) is also an input to the Brake ECM. The Brake ECM communicates the status of the brake switch to the Engine ECM via the Cat Data Link. The Engine ECM controls the compression brake application (if equipped). The front brake switch (4) is installed on machines with caliper type front brakes. When activated, the front brake switch sends a signal to the Brake ECM which allows the front brakes to be engaged when the brake pedal is depressed. When the front brake switch is in the OFF position, only the rear brakes will be engaged when the brake pedal is depressed.



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Text Reference



3



1 87



2



3



88



The 777F has two slack adjusters. The top illustration shows the rear slack adjuster (1). The rear slack adjuster is located above the rear differential. The bottom illustration shows the front slack adjuster (2). The front slack adjuster is located on the left strut frame support. The slack adjusters compensate for brake disc wear by allowing a small volume of oil to flow through the slack adjuster and remain between the slack adjuster and the brake piston under low pressure. The slack adjusters maintain a slight pressure on the brake piston at all times. Brake cooling oil pressure maintains a small clearance between the brake discs. The service brake oil pressure can be tested at the taps (3) located on top of the slack adjusters.



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Text Reference



BRAKE SLACK ADJUSTER Oil Flow To Brake Cylinder



Small Piston



Large Piston



Oil Flow From Brake Cylinder



From Wheel Brakes



From Wheel Brakes



To Wheel Brakes To Wheel Brakes



BRAKES RELEASED



BRAKES ENGAGED



89



This illustration shows sectional views of the slack adjuster when the brakes are RELEASED and ENGAGED. When the brakes are ENGAGED, oil from the brake cylinder enters the slack adjuster and the two large pistons move outward. Each large piston supplies oil to one wheel brake. The large pistons pressurize the oil to the service brake pistons and ENGAGE the brakes. Normally, the service brakes are FULLY ENGAGED before the large pistons in the slack adjuster reach the end of their stroke. As the brake discs wear, the service brake piston will travel farther to FULLY ENGAGE the brakes. When the service brake piston travels farther, the large piston in the slack adjuster moves farther out and contacts the end cover. The pressure in the slack adjuster increases until the small piston moves and allows makeup oil from the brake cylinder to flow to the service brake piston. When the brakes are RELEASED, the springs in the service brakes push the service brake pistons away from the brake discs. The oil from the service brake pistons pushes the large pistons in the slack adjuster to the center of the slack adjuster. Makeup oil that was used to ENGAGE the brakes is replenished at the brake cylinder from the makeup tank.



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Text Reference



The spring behind the large piston causes some oil pressure to be felt on the service brake piston when the brakes are RELEASED. Keeping some pressure on the brake piston provides rapid brake engagement with a minimum amount of brake cylinder piston travel. The slack adjusters can be checked for correct operation by opening the service brake bleed screw with the brakes RELEASED. A small amount of oil should flow from the bleed screw when the screw is opened. The small flow of oil verifies that the spring behind the large piston in the slack adjuster is maintaining some pressure on the service brake piston. A more accurate test for the slack adjuster is discussed on the next page.



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Text Reference



1



2



90



The service brake bleed screw (1) is identified by an "S" on the brake anchor plate casting next to the screw. The parking brake bleed screw (2) is identified by a "P" on the casting. Another check to verify correct slack adjuster operation is to connect a gauge to the pressure tap on top of the slack adjuster and another gauge at the service brake bleed screw location on the brake anchor plate casting. With the service brake pedal depressed, the pressure reading on both gauges should be approximately the same. When the brakes are RELEASED, the pressure at the slack adjuster should return to zero. The pressure at the service brake bleed screw location should return to the residual pressure held on the brakes by the slack adjuster piston. If the slack adjuster residual pressure is too low, it could indicate a failed slack adjuster. High residual pressure may indicate a failed slack adjuster or warped brake discs. To check for warped brake discs, rotate the wheel to see if the pressure fluctuates. If the pressure fluctuates while rotating the wheel, the brake discs are probably warped and should be replaced. To check for brake cooling oil leakage, block the brake cooling ports and pressurize each brake assembly to a maximum of 138 kPa (20 psi). Close off the air supply source and observe the pressure trapped in the brake assembly for five minutes. The trapped pressure should not decrease.



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Text Reference



91



1



4 3



1



92 2



The parking brake valve (1) is located on the inside left frame rail behind the center cross member. The parking valve receives oil flow from the parking brake accumulator. Contained within the valve is a parking brake solenoid valve (2) and a purge solenoid valve (3). When the parking brake solenoid is energized by the Brake ECM, the parking brake valve directs oil flow through the TCS valve to release the rear parking brakes. There are no parking brakes on the front wheels. When the transmission shift lever is moved to PARK a signal is sent to the Brake ECM to engage the parking brakes. There is not a separate parking brake control switch. The secondary brake pressure switch (4) sends a signal to inform the Transmission/Chassis ECM that the secondary/parking brake is engaged. When the machine is shut down, the purge solenoid is energized by the Transmission/Chassis ECM and the purge valve drains the brake accumulators to tank.



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Text Reference



1 2



93



The parking brake pressure can be checked at the left parking brake tap (1) and at the right parking brake tap (2).



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Text Reference



94



The secondary brake pedal position sensor (arrow) is located on the back of the secondary brake pedal. The position sensor sends a signal to the Brake ECM indicating the position of the secondary brake pedal. The Brake ECM sends a signal to the parking brake solenoid which controls the secondary brake application at the rear brakes.



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Text Reference



95



The secondary steering/brake release/QuickEvac pump and motor are located on the front of the front crossmember as previously shown. The brake retract pump section (arrow) provides oil to release the parking brakes and hoist pilot oil for lowering the body on trucks with a dead engine.



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Text Reference



96



The diverter (towing) valve (arrow) is located on the left hoist cylinder frame support. The diverter valve is used to unlock the brakes for towing and must be manually shifted before towing. Once the valve is shifted, oil flow from the electric secondary steering/brake retract pump is directed to the parking brake valve to release the parking brake. To release the parking brakes for service work or towing, the electric motor on the pump is energized by the brake release switch located in the cab. When the key start switch is turned ON, the secondary steering system is energized for three seconds to check the system. Since the towing pump is driven by the same electric motor as the secondary steering pump, the diverter valve allows the towing pump oil to flow directly to the hydraulic tank during the secondary steering test. To shift the diverter valve, loosen the two diverter valve clamp bolts and slide the plate and the spool to the left. After the spool is shifted, tighten the diverter valve clamp bolts. When the electric motor is energized, supply oil can flow from the towing pump, through the diverter valve, to the parking brake valve. The brake release pump is also used to provide pilot oil to lower the body when the engine is off.



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Text Reference



BRAKE COOLING SYSTEM OIL COOLED FRONT BRAKES



Front Brakes



Hoist, Converter, and Brake Oil Coolers



Right



Left



Rear Brakes



Screen



Right



Hoist Valve Screen



From Brake Cooling Pump



Left



Torque Converter Charging Filter Inlet Relief Valve



To Variable Speed Clutch Control To Hoist Pilot Signal Resolver



Lockup Clutch Valve



Outlet Relief Valve



Lockup Relief Valve



Lockup Clutch Filter



To TCS Converter Valve Scavenge Screen



97



This schematic shows the oil flow through the brake cooling system on the 777F Trucks with standard oil cooled front brakes. The brake cooling pump supplies oil to the brake coolers and the front and rear brakes. The brake cooling system also receives oil from the following components: - Hoist valve (in the HOLD, FLOAT, and SNUB positions) - Accumulator charging valve - Torque converter lockup clutch relief valve - Torque converter outlet relief valve The pressure in the brake cooling system is limited by a relief valve located in the hoist valve. The relief valve is usually needed only when the brake cooling oil is cold. When brake cooling oil is at operating temperature, the brake cooling oil pressure is usually much lower than the setting of the oil cooling relief valve. NOTE: On trucks equipped with the optional caliper type front brakes, the brake cooling system oil flows only to the rear brakes.



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Text Reference



2



1 98 3



The brake cooling pump (1) is a gear type pump that is attached to the drive gear at the rear of the engine. The brake cooling pump is located between the hoist pump (2) and the brake charging pump (3). Oil flows from the brake cooling pump to the brake oil coolers. NOTE: The brake oil cooling pump is not installed on trucks with the optional caliper type front brakes.



99



The brake oil coolers (arrows) are located on the right side of the engine. Engine coolant from the water pump flows around the brake oil coolers and back to the cylinder block. The engine coolant transfers the heat from the brake oil system to the engine coolant. Oil from the brake cooling pump flows through screens (not shown) before flowing through the brake oil coolers.



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Text Reference



100



Shown is the left rear brake housing. Brake cooling oil pressure can be tested at the two taps (arrows) located in the brake cooling oil tubes. One tap is located on the brake cooling inlet tube and another tap is located on the brake cooling outlet tube. The pressure measured at the brake inlet tube (from the oil coolers) will always be higher than the pressure measured at the brake outlet tube. A brake oil temperature sensor is located in a brake oil cooling tube on the truck. The brake oil temperature sensor sends a signal to the Brake ECM indicating brake oil temperature. The Brake ECM will send a signal over the Cat Data Link, which informs the monitoring system to display the temperature on the brake temperature gauge. The most common cause of high brake cooling oil temperature is operating the truck in a gear range which is too high for the grade and not maintaining a high enough engine speed. The engine speed should be maintained at approximately 1900 rpm during long downhill hauls. Make sure the oil cooling relief valve is not stuck open. Also, make sure the pistons in the slack adjuster are not stuck and holding too much pressure on the brakes.



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Text Reference



BRAKE HYDRAULIC SYSTEM



Left Rear Brake



Secondary Brake Pedal Position Sensor



Diverter Valve



Parking Brake Solenoid



ECM



Relief Valve



Parking Brake Valve



Service Brake Pedal Position Sensor



Service Brake Valve



ARC Control



Purge Valve



Left Front Brake Cab Brake Manifold



M Secondary Pump



Parking Brake Accumulator Service Brake Accumulators



From TC Lockup Clutch Pump TCS Valve



Switch Cut-In / Cut-Out Spool



Unloading Valve Slack Adjuster



To Brake Cooling



Accumulator Charging Valve Relief Valve



Brake Filter



From TC Valve



Right Front Brake



Right Rear Brake



101



This schematic shows the major components of the brake system with the standard oil cooled front brakes. The front slack adjuster is not included on the optional caliper type front brake system. Oil is drawn from the hydraulic tank by the brake charging pump. Oil flows through the brake filter to the accumulator charging valve. The accumulator charging valve directs supply oil to the brake accumulators. The accumulator charging valve also controls the cut-in and cut-out pressure. When the accumulators are charged, the charging valve will direct excess pump flow to the brake cooling system. The service brake accumulators provide oil flow through the cab manifold to the service brake control valve. Oil flowing into the cab manifold also flows to the ARC control solenoid and front brake solenoid. When the operator depresses the service brake pedal, the service brake control valve directs pump flow to the rear service brakes to stop the truck. The front brakes are only engaged when the Brake ECM energizes the front brake solenoid. With the standard oil cooled front brakes, the Brake ECM determines when to energize the front brake solenoid when the service brake pedal is depressed. With the optional caliper type front brakes, the Brake ECM will energize the front brake solenoid when the front brake lockout switch in the cab is activated.



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Text Reference



The Brake ECM controls the modulation of the ARC solenoid and front brake solenoid, which controls truck braking when the ARC system is ON. Oil from the parking brake accumulator flows to the parking brake valve and the towing diverter valve. When the parking brake is activated, the supply oil for releasing the parking brakes is directed to the tank and the parking brakes are engaged by spring force. When the parking brake solenoid is energized (parking brake de-activated), the parking brake valve directs oil to the TCS valve. The pressure reducing valves in the TCS valve direct oil to release the parking brakes. The diverter valve, under normal operation, is closed and blocks the oil flow from the electric brake retract pump. If the truck is to be towed with a dead engine, the diverter valve must be shifted manually. When manually shifted, the diverter valve directs oil flow from the electric brake retract pump to the parking brake valve to release the rear brakes.



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Text Reference



BRAKE CONTROL MODULE SYSTEM DIAGRAM Cat Data Link



INPUTS



OUTPUTS



Key Start Switch Accumulator Oil Pressure Switch Brake Filter Bypass Switch TCS Test Switch



Secondary Brake Pedal Position Sensor Service Brake Pedal Position Sensor Retarder Lever Engine Speed Sensor



ARC ON/OFF Switch



Compression ON/OFF Switch Front Brake Lockout Switch



Left Rear Wheel Speed Sensor



ARC Control Solenoid Front Service Brake Solenoid Parking Brake Solenoid TCS Proportional Solenoid TCS Selector Solenoid



Right Rear Wheel Speed Sensor Brake Oil Temperature Sensor



102



Brake Electronic Control System The 777F Trucks are equipped with a Brake ECM for controlling the parking brake and front service brake applications, the ARC system, and the TCS. Two possible arrangements can be installed on a truck: - ARC only - ARC and TCS The Brake ECM receives information from various input components such as the engine speed sensor, the service brake pedal position sensor, the ARC switch, and the wheel speed sensors. Based on the input information, the Brake ECM controls the front service brake application when the service brake pedal is depressed or the front and rear service brake application when the ARC system is activated. The Brake ECM also controls when the parking brakes should engage for the TCS and parking brake application when the parking brake is manually activated.



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Text Reference



Output components include the ARC solenoid, the front service brake solenoid, the TCS selector and proportional solenoids, and the parking brake solenoid. The compression brake switch is also an input to the Brake ECM. When the compression brake switch is activated, the Brake ECM sends a signal over the Cat Data Link to the Engine ECM. The Engine ECM controls the engine compression brake, which was covered earlier in the presentation.



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Text Reference



103



The Brake ECM (arrow) is located in the compartment at the rear of the cab. The Brake ECM performs the brake control functions, and controls the ARC system and TCS. The Brake ECM is an A4M1 module with two 70-pin connectors. The Brake ECM communicates with the Engine ECM, Transmission/Chassis ECM, and monitoring system over the CAT Data Link and can communicate with some attachments over the CAN Datalink.



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Text Reference



SERVICE / RETARDER BRAKE CIRCUIT BRAKES RELEASED



Service Brake Pedal Position Sensor To Rear Service Brakes ARC Solenoid



Service Brake Valve



From Service Brake Accumulators



Retarder Lever Brake ECM



Front Service Brake Solenoid



To Front Service Brakes



Front Brake Lockout Switch (Caliper Type Front Brakes)



Cab Manifold



104



When the service brake pedal is depressed, the service brake valve directs oil from the service brake accumulators to the rear brakes and sends a PWM signal to the Brake ECM via the service brake pedal position sensor. The Brake ECM then determines what signal to send to the front service brake solenoid based on the following conditions: 1. If the truck is equipped with the standard oil cooled front brakes, the Brake ECM signals the front service brake solenoid to direct oil from the service brake accumulators to the front and rear brakes. 2. If the truck is equipped with the optional caliper type front brakes, the Brake ECM receives a signal from the front brake lockout switch in the cab. If the lockout switch is OFF, the Brake ECM signals the front service brake solenoid to direct oil from the service brake accumulators to the front and rear brakes the same as the oil cooled front brakes. NOTE: Oil flow to the front and rear brakes may not be proportional. When the pedal is initially depressed, more oil is directed to the rear brakes. As the pedal is depressed farther more oil is sent to the front brakes in proportion to the rear until full front brake pressure is present at full pedal travel.



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3. If the truck is equipped with the optional caliper type front brakes, and the lockout switch is ON, the Brake ECM de-energizes the front service brake solenoid. Oil flow to the front brakes is blocked and only the rear brakes are used to stop the truck. The Brake ECM also de-energizes the ARC solenoid when the ARC switch in the cab is OFF and the manual retarder lever is in the NEUTRAL position. The manual retarder lever also controls the service brake application using the front brake solenoid and the ARC solenoid. When the retarder lever is moved, a PWM signal is sent to the Brake ECM. The Brake ECM then determines what signal to send to the ARC solenoid and front service brake solenoid based on the following conditions: 1. If the truck is equipped with the standard oil cooled front brakes, the Brake ECM signals the ARC solenoid and the front service brake solenoid to divide the oil flow from the service brake accumulators between the front and rear brakes. 2. If the truck is equipped with the optional caliper type front brakes, the Brake ECM de-energizes the front service brake solenoid. Oil flow to the front brakes is blocked and only the rear brakes are used to stop the truck with the retarder lever.



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AUTOMATIC RETARDER CONTROL (ARC) To Rear Service Brakes ARC Solenoid



Service Brake Valve



From Service Brake Accumulators



Brake ECM



Front Service Brake Solenoid



Engine Speed Sensor ARC ON/OFF Switch



To Front Service Brakes



Cab Manifold



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Automatic Retarder Control (ARC) The ARC system receives signals from several switches and sensors. The main inputs to the Brake ECM for the ARC system are the ARC switch and engine speed sensor. The Brake ECM analyzes the various input signals and sends output signals to the ARC solenoid and front service brake solenoid. NOTE: If the truck is equipped with the optional front caliper type brakes, the Brake ECM will de-energize the front service brake solenoid when the ARC system is activated. The ARC system function is to modulate truck braking (retarding) when descending a long grade to maintain a constant engine speed. The ARC system engages the rear service brakes and the front oil cooled service brakes. If the ARC switch is moved to the ON position, the ARC system will be activated if the throttle pedal is not depressed and the parking/secondary brakes are RELEASED. The ARC system is disabled when the throttle is depressed or when the parking/secondary brakes are ENGAGED.



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The ARC is set at the factory to maintain a constant engine speed of 1900 ± 50 rpm (engine speed setting is programmable). When the ARC initially takes control of retarding, the engine speed may oscillate out of the ± 50 rpm target, but the engine speed should stabilize within a few seconds. For proper operation of the ARC system, the operator needs only to activate the control with the ARC switch and select the correct gear for the grade, load, and ground conditions. The ARC system is designed to allow the transmission to upshift to the gear selected by the shift lever. After the transmission shifts to the gear selected by the operator and the engine speed exceeds 1900 rpm, the ARC system will apply the retarder as needed to maintain a constant engine speed. The ARC system also provides engine overspeed protection. If an unsafe engine speed is reached, the ARC will engage the brakes, even if the ARC switch is in the OFF position and the throttle is depressed. Trucks approaching an overspeed condition will sound a horn and activate a light at 2100 rpm. If the operator ignores the light and horn, the ARC will engage the retarder at 2180 rpm. If the engine speed continues to increase, the Transmission/Chassis ECM will either upshift (one gear only above shift lever position) or unlock the torque converter (if the shift lever is in the top gear position) at 2300 rpm. The ARC also provides service personnel with enhanced diagnostic capabilities through the use of onboard memory, which stores possible faults, solenoid cycle counts and other service information for retrieval at the time of service.



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TRACTION CONTROL SYSTEM ( TCS)



INPUTS



OUTPUTS



Left Rear Wheel Speed Sensor



TCS Proportional Solenoid



Right Rear Wheel Speed Sensor



TCS Selector Solenoid



TCS Test Switch Service Brake Pressure Switch



Cat Data Link



Transmission Output Speed Sensor 1 Transmission Output Speed Sensor 2



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Traction Control System (TCS) The Traction Control System (TCS) uses the rear parking/secondary brakes (spring engaged and hydraulically released) to decrease the revolutions of a spinning wheel. The TCS allows the tire with better underfoot conditions to receive an increased amount of torque. The system is controlled by the Brake ECM and operates the same as the 777D TCS. The Brake ECM monitors the drive wheels through three input signals: one at each drive axle, and one at the transmission output shaft. When a spinning drive wheel is detected, the Brake ECM sends a signal to the selector and proportional valves which ENGAGE the brake of the affected wheel. When the condition has improved and the ratio between the right and left axles returns to 1:1, the Brake ECM sends a signal to RELEASE the brake.



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The service brake pressure switch provides an input signal to the Brake ECM from the Transmission/Chassis ECM through the CAT Data Link and performs two functions: 1. When the service brakes or retarder are ENGAGED, the TCS function is stopped. 2. The service brake pressure switch provides the input signal needed to perform a diagnostic test. When the TCS test switch and the retarder lever are ENGAGED simultaneously, the TCS will engage each rear brake independently. Install two pressure gauges on the TCS valve, and observe the pressure readings during the test cycle. The left brake pressure will decrease and increase. After a short pause, the right brake pressure will decrease and increase. The test will repeat as long as the TCS test switch and the retarder lever are ENGAGED. The TCS valve has left and right brake release pressure taps. Cat ET can also be used to view the left and right parking brake pressures during the test discussed above in function No. 2. When the proportional solenoid is ENERGIZED, Cat ET will show 44% when the brake is FULLY ENGAGED. NOTE: During the diagnostic test, the parking/secondary brakes must be released.



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Shown is the right rear wheel speed sensor (arrow) looking toward the rear of the truck. The TCS monitors the drive wheels through four input speed signals: one at each drive axle, and two at the transmission output shaft. The transmission output speed sensors monitor the ground speed of the machine and provide input signals to the Brake ECM through the CAT Data Link. The TCS uses the transmission output speed sensors to disable the TCS when ground speed is above 19.3 km/h (12 mph).



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2 1



3 3



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The TCS valve is mounted inside the left frame rail toward the rear of the machine. Two solenoids are mounted on the valve. Electrical signals from the Brake ECM cause the selector solenoid valve (1) to shift and select either the left or right parking brake. If the selector valve shifts to the left parking brake hydraulic circuit, the control oil is drained. The left reducing spool of the control valve can then shift and engage the parking brake. The proportional solenoid valve (2) controls the volume of oil being drained from the selected parking brake control circuit. The rate of flow is controlled by a signal from the Brake ECM. The pressure taps (3) can be used to test the left and right brake release pressures when performing diagnostic tests on the TCS. At HIGH IDLE, the pressure at the taps in the TCS valve will be approximately 138 kPa (20 psi) less than the brake release pressure tested at the wheels. The pressure taps are also used to provide parking brake dragging information to the service technician. If the parking brakes are released, as sensed by the secondary brake pressure switch on the parking brake control valve, and parking brake pressure is below 3445 kPa (500 psi), a parking brake dragging event will be logged in the Brake ECM. The event can be viewed with Cat ET.



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TCS VALVE



ENGINE RUNNING / BRAKES RELEASED From Parking Brake Valve



From TC Lockup Clutch Pump



To Left Rear Brake



Brake Reducing Valve



Proportional Solenoid



Selector Solenoid Brake Reducing Valve



To Right Rear Brake



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This illustration shows the TCS valve with the engine running and the brakes RELEASED. With the engine running, oil flows from the brake charging pump to the parking brake valve. When the operator moves the transmission lever out of the PARK position, the Brake ECM energizes the parking brake solenoid which directs oil flow to the TCS valve. In the TCS valve, oil flows through a screen and orifices to the selector solenoid and the brake reducing valves. When the TCS is not activated, the oil is blocked at the selector solenoid. Oil pressure moves the brake reducing solenoids to the left and oil from the brake charging pump is directed to the parking brakes. The parking brakes are RELEASED.



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TCS VALVE



ENGINE RUNNING / LEFT BRAKE ENGAGED To Left From Parking Rear Brake Brake Valve



From TC Lockup Clutch Pump



Brake Reducing Valve Proportional Solenoid



Selector Solenoid Brake Reducing Valve



To Right Rear Brake



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This illustration shows the TCS valve with the engine running and the left brake ENGAGED. When signals from the sensors indicate that the left wheel is spinning 60% faster than the right wheel, the Brake ECM sends a signal to the selector solenoid valve and the proportional solenoid valve. The selector solenoid valve shifts up to open a passage between the right end of the left brake pressure reducing valve and the proportional solenoid valve. The torque converter lockup pump oil provides signal oil to the drain ball check which allows oil from the TCS valve to return to the tank. The proportional solenoid valve opens a passage from the selector solenoid valve to drain through the drain ball check. The proportional solenoid valve also controls the rate at which the oil is allowed to drain. Control circuit oil drains through the selector valve and enters the proportional valve.



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The reducing valve spool for the left parking brake shifts and blocks oil flow to the parking brake. Oil in the left parking brake control circuit begins to drain and the left parking brake begins to ENGAGE. The left brake orifice restricts the flow of oil from the parking brake valve. When the signals from the sensors indicate that the left wheel is no longer spinning, the Brake ECM stops sending signals to the selector solenoid and the proportional solenoid. The selector solenoid valve and proportional solenoid valve block the passage to drain and allow the control circuit pressure to increase. The left brake reducing valve spool shifts to the left and blocks the passage to drain. Parking brake oil is directed to the left parking brake and the brake is RELEASED.



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CONCLUSION This presentation has provided a basic introduction to the Caterpillar 777F Off-highway Truck. All the major component locations were identified and the major systems were discussed. When used in conjunction with the service manual, the information in this package should permit the technician to analyze problems in any of the major systems on these trucks.