Service TrainingSEBV2591 April 1994 SLIDE/TEXT REFERENCE 793B PART OF TECHNICAL INSTRUCTION MODULE SEGV2591 769C - 793B OFF-HIGHWAY TRUCKS TORQUE CONVERTER AND TRANSMISSION HYDRAULIC SYSTEMS SEBV2591 -2- Table of Contents 4/94 TABLE OF CONTENTS INTRODUCTION ..................................................................................................................3 POWER TRAIN ....................................................................................................................4 TORQUE CONVERTER........................................................................................................5 TORQUE CONVERTER HYDRAULIC SYSTEM ..............................................................8 TRANSMISSION HYDRAULIC SYSTEM........................................................................21 SEBV2591 -3- 4/94 1 INTRODUCTION • Introduce course This module is designed to introduce service technicians to the torque converter and transmission hydraulic systems used in Cat Off-highway Trucks. Emphasis is placed on system component location and function. • Module divided into In the first section of this module, the discussion concentrates on the two parts torque converter hydraulic system, and the last section covers the transmission hydraulic system, specifically the Individual Clutch Modulation (ICM) control valve group. • Off-highway Trucks The trucks are divided into two groups: 769C - 777C (small) and the divided into two 785B - 793B (large). Many of the component locations shown will use groups: the 769C truck since all the trucks have the same basic components. If - 769C - 777C another truck is shown, the model number will be stated. - 785B - 793B Gray Transfer gears .Green Transmission . This shop exercise will provide familiarization with the major power Introduce and perform train components.Blue Drive shaft . Lab A . Objective 1 INSTRUCTOR NOTE: At this time. introduce and perform Lab A: Slide 2 Torque Converter and Transmission Component Location Identification.SEBV2591 -4- 4/94 LOCKUP MODULATION VALVE TRANSMISSION PUMP TORQUE CONVERTER SOLENOIDS TYPICAL OFF-HIGHWAY TRUCK POWER TRAIN COMPONENT LOCATIONS TRANSMISSION TORQUE TRANSMISSION CONVERTER FILTER OIL FILTER TORQUE CONVERTER INLET AND AND TRANSMISSION OIL OUTLET RELIEF VALVES TRANSMISSION DRIVE CONTROL VALVE SHAFT TRANSMISSION DIFFERENTIAL AND FINAL DRIVES LOCKUP CLUTCH TORQUE TORQUE CONVERTER CONVERTER PUMP TRANSFER GEARS 2 POWER TRAIN • Identify components Power flows from the engine through the power train to the rear wheels. power from the torque converter is directed through the differential and the final drives to the rear wheels.Purple After the transmission engages two clutches. The major components of the power train are: • Explain power flow Torque converter . Speeds 1 to 7 SECOND through SEVENTH SPEEDS are direct drive only. Torque converter The first component in the power train is the torque converter (1). R. . the torque converter inlet relief valve (3) and the torque control valve converter lockup clutch control valve (4). At higher ground speeds. .18 . the torque torque converter drive converter multiplies torque to the transmission. Objectives 2 and 5 Slides 3 . Inlet relief valve Mounted on the torque converter housing are the torque converter outlet 4. The first half of FIRST SPEED is converter drive (low ground in direct drive speed) and the second half is direct drive (higher ground speed).Speeds N. 1 a lockup clutch engages to provide direct drive for more efficient operation. The torque converter goes to converter drive between each shift (during clutch 2. The torque converter provides a fluid coupling that permits the engine to • Fluid coupling in continue running with the truck stopped. In converter drive. Outlet relief valve engagement) to provide smooth shifts. Lockup clutch relief valve (2). Pressure in the converter is controlled by restriction in the line between the converter and the hydraulic tank. 3.SEBV2591 -5- 4/94 4 3 1 2 3 TORQUE CONVERTER 1. NOTE: The 773B and 775B do not have a torque converter outlet relief valve. The NEUTRAL and REVERSE ranges are converter drive • Mechanical coupling only. . The stator remains stationary and directs most of the oil back to the impeller. During operation. The stator multiplies the torque transfer between the impeller and the turbine by changing the direction of the oil flowing from the turbine to the same direction as the impeller. The rotating housing and impeller direct the oil into the blades of the turbine (blue) and cause the turbine to rotate.SEBV2591 -6- 4/94 LOCKUP PISTON TURBINE IMPELLER TORQUE CONVERTER INLET OIL STATOR TORQUE CONVERTER LOCKUP OIL PASSAGE FREEWHEEL ASSEMBLY TORQUE CONVERTER CONVERTER DRIVE 4 • CONVERTER DRIVE This sectional view shows a torque converter in CONVERTER DRIVE. The lockup clutch (yellow piston and blue discs) is not engaged. The turbine and the output shaft rotate slower than the engine and the impeller. The rotating housing and impeller (red) are connected to the engine flywheel. The freewheel assembly only allows the stator to rotate in the same direction as the turbine. but with increased torque. oil flows from the torque converter inlet relief valve to the impeller. The turbine directs the oil to the stator (green) and causes the stator to try to rotate in the opposite direction of the turbine. turbine. The housing. and output shaft then rotate as a unit at engine rpm. which is mounted on a freewheel assembly. the lockup clutch is engaged by hydraulic pressure and locks the turbine to the impeller.SEBV2591 -7- 4/94 LOCKUP PISTON TURBINE IMPELLER TORQUE CONVERTER INLET OIL STATOR TORQUE CONVERTER LOCKUP OIL PASSAGE FREEWHEEL ASSEMBLY TORQUE CONVERTER DIRECT DRIVE 5 • DIRECT DRIVE In DIRECT DRIVE. . impeller. The stator. is driven by the force of the oil in the housing and will freewheel at approximately the same rpm. Torque converter charging .Parking brake release Excess oil that accumulates in the bottom of the torque converter is 2. . Screen scavenged by the first section of the pump through a screen (2) and returned to the hydraulic tank.SEBV2591 -8- 4/94 1 2 6 TORQUE CONVERTER HYDRAULIC SYSTEM 1. The three sections (from the right to the left) are: .Parking brake release . Torque converter The three section torque converter pump (1) is located at the bottom rear pump sections: of the torque converter.Torque converter scavenge .Scavenge .Charging . Charging filter Oil flows from the torque converter charging section of the pump to the torque converter charging filter (1) located in front of the transmission (2) 2. Transmission just behind the transmission oil filter (3).SEBV2591 -9- 4/94 3 1 2 7 1. 3. Transmission oil filter . The outlet relief pressure can be measured at the test location (4). 4. The outlet relief valve controls the maximum pressure in the torque converter. . Oil in the torque converter either falls to the bottom of the housing to be scavenged or flows through the torque converter outlet relief valve (3). Test location relief valve (1).SEBV2591 .10 - 4/94 1 3 2 4 8 1. The torque converter inlet relief 3. Test location Oil flows through the inlet relief valve and enters the torque converter. Outlet relief valve pressure can be measured at the test location (2) (hidden by hose). The inlet relief valve controls the maximum pressure of the supply oil to the torque converter. Inlet relief valve Oil flows from the torque converter oil filter to the torque converter inlet 2. Scavenge . Oil from this filter flows to the parking brake release valve.Release the parking brakes 2. Optional front brake release filter.Brake oil cooling lockup Oil flows from the parking brake release section to the parking brake 4.11 - 4/94 3 2 1 4 9 • Torque converter The parking brake release section (3) of the torque converter pump pump sections: (777C) provides supply oil for several purposes: 1. cooling The parking brake release valve controls the pressure for parking brake release and torque converter lockup.Engage the torque converter lockup clutch 3. Charging . Most of the oil from the parking brake release valve flows to the brakes for cooling. Parking brake release/converter .SEBV2591 . INSTRUCTOR NOTE : The torque converter pump includes the following sections: (1) Torque converter scavenge (2) Torque converter charging (3) Parking brake release/converter lockup (4) Optional front brake cooling . .SEBV2591 .12 - 4/94 10 • Parking brake release Oil flows from the parking brake release section of the torque converter filter (arrow) pump to the parking brake release filter (arrow). pressure tap Torque converter lockup clutch pressure can be measured at the tap (5). 2. Lockup clutch and solenoid valve The torque converter lockup clutch and solenoid valve (2) receive supply 3.13 - 4/94 3 4 1 2 5 11 1. Solenoid valve supplies oil at a reduced pressure to lock up the torque converter 5.SEBV2591 . the lockup clutch 4. . Hose oil from the parking brake release valve through a hose (3). Parking brake Oil from the parking brake release filter flows to the parking brake release release valve valve (1) on the 777C. When the solenoid (4) is energized by the transmission control. Lockup clutch and go into direct drive. 18 Yellow .Moving components .Drain or reservoir oil Red and White Stripes .Lockup clutch pressure Brown . In this illustration and those that follow. Supply oil NEUTRAL from the parking brake release pump is used to provide lockup clutch oil and has two functions: 1. When the solenoid is energized.Supply oil pressure Green .Lubrication or cooling pressure Objective 4 Orange . supply pressure is reduced by the modulation reduction valve to provide lockup clutch pressure. the colors used to identify the various pressures in the systems are as follows: Red . Supply pressure is reduced to provide pilot pressure to the solenoid valve.14 - 4/94 LOCKUP CLUTCH VALVE TORQUE CONVERTER DRIVE LOAD SELECTOR PISTON PISTON MODULATION LOAD PISTON REDUCTION ORIFICE VALVE PRESSURE REDUCTION VALVE LOCKUP SOLENOID SHUTTLE TO FROM VALVE LOCKUP PARKING BRAKE CLUTCH PUMP 12 • Lockup clutch and Shown is a sectional view of the torque converter lockup clutch solenoid solenoid valve in valve in TORQUE CONVERTER DRIVE or NEUTRAL.SEBV2591 .Pilot or torque converter pressure Slides 12 . 2. As the clutch fills.15 - 4/94 LOCKUP CLUTCH VALVE CLUTCH FILLING LOAD SELECTOR PISTON PISTON LOAD PISTON ORIFICE MODULATION REDUCTION VALVE PRESSURE REDUCTION VALVE LOCKUP SOLENOID ON SHUTTLE FROM VALVE TO LOCKUP CLUTCH PARKING BRAKE PUMP 13 • Lockup solenoid In this sectional view. The load piston orifice provides a pressure drop and time delay in the flow of oil to the load piston chamber. Oil then flows to the selector piston. Before moving the selector piston. . pressure oil opens the ball check valve and fills the slug chamber at the top of the reduction valve spool. Filling the load piston chamber is made possible when the selector piston covers the drain passage at the decay orifice. The load piston orifice helps control the rate of modulation. oil flows through the load piston orifice and fills the chamber between the end of the load piston and the selector piston. clutch modulation pilot oil moves the shuttle valve to the right which closes the drain and opens the check valve. Moving the selector piston blocks the drain passage and the load piston springs are compressed. This initial movement opens the supply passage (from the parking brake pump) and permits pressure oil to flow to the clutch. At the same time. Compressing the load piston springs moves the modulation reduction valve spool down against the force of the inner spring. the lockup solenoid has been energized and directs energized starts pilot pressure to the selector piston.SEBV2591 . If the primary pressure is correct and final lockup clutch pressure is low. the pressure in the slug chamber moves the reduction valve a small distance up to restrict the flow of supply oil to the clutch. If the load piston moves freely. the maximum pressure setting of the clutch is lower than the pilot and parking brake release pressure. The maximum pressure modulation cycle is completed and the clutch pressure is at its maximum setting. the load piston springs should be replaced. Because this is a modulation reduction valve.SEBV2591 . In this position. At the end of the modulation cycle. .16 - 4/94 LOCKUP CLUTCH VALVE DIRECT DRIVE LOAD SELECTOR PISTON PISTON LOAD PISTON ORIFICE MODULATION REDUCTION VALVE PRESSURE REDUCTION VALVE LOCKUP SOLENOID ON SHUTTLE TO VALVE FROM LOCKUP PARKING BRAKE CLUTCH PUMP 14 • Lockup clutch at The load piston has now moved completely down against the stop. the load piston should be checked to make sure that it moves freely in the selector piston. Primary pressure is adjusted with shims in the load piston. This is the "metering position" of reduction valve spool. Final lockup clutch pressure is not adjustable. the valve maintains precise control of the clutch pressure. and solenoid valve. . the torque converter lockup clutch.SEBV2591 . NOTE: The 773B and 775B do not have an outlet relief valve. Most of the oil flows through the parking brake release valve to the brake cooling system.17 - 4/94 769C . The parking brake release pump section sends oil to the parking brake release valve. The charging pump section sends oil through the torque converter charging filter to the inlet relief valve and torque converter.777C TORQUE CONVERTER HYDRAULIC SYSTEM NEUTRAL LOCKUP CLUTCH PILOT OIL PRESSURE LOCKUP CLUTCH BRAKE COOLING OUTLET PRESSURE PRESSURE PRESSURE LOCKUP MODULATION VALVE OUTLET TO BRAKE RELIEF VALVE COOLING CIRCUIT INLET RELIEF VALVE INLET PRESSURE LOCKUP SOLENOID LOCKUP REDUCING VALVE TO BRAKE COOLING TORQUE CIRCUIT CONVERTER PARKING BRAKE LOCKUP RELEASE VALVE CLUTCH CONVERTER SCAVENGE PUMP PARKING BRAKE RELEASE PRESSURE CONVERTER PARKING CHARGING BRAKE PUMP RELEASE PUMP SCREEN 15 • Small truck torque This schematic shows the flow of oil from the torque converter charging converter hydraulic pump through the 769C .777C hydraulic system. Oil flows from the outlet relief valve to the brake cooling system. schematic The scavenge pump section scavenges oil through a screen in the torque converter housing and sends the oil to the hydraulic tank. Oil flows through the torque converter to the outlet relief valve. 18 - 4/94 785B .SEBV2591 .793B TORQUE CONVERTER LOCKUP CLUTCH CONTROL CONVERTER DRIVE LOCKUP CLUTCH PILOT OIL PRESSURE LOCKUP MODULATION LOCKUP VALVE SOLENOID TO LOCKUP CLUTCH TRANSMISSION PUMP LOCKUP OIL PRESSURE REDUCING VALVE FROM TRANSMISSION PUMP SHUTTLE VALVE TORQUE CONVERTER RELAY VALVE FROM PARKING BRAKE PUMP 16 • Large truck lockup This schematic shows the 785B . .793B torque converter hydraulic system components in with emphasis on the lockup components in TORQUE CONVERTER NEUTRAL DRIVE or NEUTRAL. 19 - 4/94 785B . The torque converter is in DIRECT DRIVE.SEBV2591 .793B TORQUE CONVERTER LOCKUP CLUTCH CONTROL DIRECT DRIVE LOCKUP CLUTCH PILOT OIL PRESSURE LOCKUP MODULATION LOCKUP VALVE SOLENOID TO LOCKUP CLUTCH TRANSMISSION PUMP LOCKUP OIL PRESSURE REDUCING ON VALVE FROM TRANSMISSION PUMP TORQUE CONVERTER RELAY VALVE FROM PARKING BRAKE PUMP 17 • Large truck torque In this schematic for the large trucks. . the ground speed has increased and converter in DIRECT the transmission has shifted into the second half of FIRST SPEED or DRIVE above. transmission oil is directed to the relay valve which then directs lockup clutch pilot oil to the lockup modulation valve to begin clutch modulation.793B TORQUE CONVERTER HYDRAULIC SYSTEM NEUTRAL LOCKUP CLUTCH PILOT OIL PRESSURE BRAKE COOLING OUTLET PRESSURE PRESSURE LOCKUP MODULATION LOCKUP VALVE OUTLET SOLENOID INLET RELIEF VALVE RELIEF VALVE INLET TRANSMISSION PRESSURE PUMP LOCKUP OIL PRESSURE REDUCING VALVE TO BRAKE FROM COOLING TRANSMISSION TORQUE CIRCUIT PUMP CONVERTER TORQUE CONVERTER CONVERTER RELAY VALVE SCAVENGE PUMP LOCKUP CLUTCH TO BRAKE COOLING PARKING BRAKE CIRCUIT RELEASE OIL PRESSURE CONVERTER CHARGING PARKING PUMP BRAKE RELEASE SCREEN PUMP PARKING BRAKE RELEASE VALVE 18 • Large truck torque This schematic shows the flow of oil from the torque converter pump converter hydraulic through the 785B . . Labs B. and E. D. These shop lab and classroom exercises will reinforce the material introduced in the preceding slide presentation.793B hydraulic system.20 - 4/94 785B . introduce and perform Labs B. The lockup solenoid is mounted on the transmission on a manifold with the upshift and the downshift solenoids. Introduce and perform INSTRUCTOR NOTE: At this time. C. and E D.SEBV2591 . When the lockup solenoid is energized. C. schematic The large truck system is very similar to the small trucks except that a torque converter relay valve is used to activate the lockup modulation valve. and 2. E. FORWARD Valve stations individually control the engagement and maximum • Large trucks have six pressure for each of the clutches in the transmission. and H). Pressure control main components that make up the control group: the pressure control valve group valve group (1). G. D. Distribution manifold The pressure control group has seven modulating reducing valves which 4. The smaller trucks have seven speeds FORWARD and the stations larger trucks have six speeds FORWARD. The D station in the larger • Small trucks have trucks is used to lower the maximum pressure in the system during seven speeds operation in direct drive. the H station is • Eight possible valve not used. Selector valve group the rotary actuator (4). the control valve group components: is mounted on top of the planetaries. 3. In the larger trucks." Each valve station is identified by a letter (A. This illustration shows the four 1. 9. Rotary actuator are referred to as "valve stations.54 . distribution manifold (3).21 - 4/94 1 2 3 4 19 TRANSMISSION HYDRAULIC SYSTEM • Selector and pressure The major component in the transmission hydraulic system is the selector control valve group and pressure control valve group. B. In the machine. selector valve group (2). F. and 12 Slides 19 . speeds FORWARD Objectives 6.SEBV2591 . C. Inside the actuator housing is a rotating vane which divides the actuator into two chambers. a single stage relief valve limits the maximum .Clutch pressure Green . In the small trucks. 4. the colors used to identify the various pressures in the systems are as follows: Red . the selector valve group is directly below the pressure has four valves: control valve group. Neutralizer valve permit engagement of the correct clutches for each gear range. The selector valve group has four functions: 1. Priority reducing valve 3. 2.Single stage (small trucks) system pressure in torque converter drive and direct drive.Lubrication or cooling pressure Orange . A priority reducing valve controls the pilot pressure and makes sure that pilot oil is available at the neutralizer valve spool before oil can flow to the remainder of the system. pressure oil from either the upshift or downshift solenoid is sent to the rotary actuator. Relief valve: 1. Pressure oil from the upshift solenoid causes the vane to rotate in one direction while pressure oil from the downshift solenoid causes the vane to rotate in the opposite direction.Dual stage (large pressure in converter drive and lowers the maximum pressure trucks) setting in direct drive. A neutralizer valve permits pilot oil to flow to the rotary selector spool when the engine is started with the rotary selector spool in the NEUTRAL position.22 - 4/94 • Selector valve group In the valve stack.Torque converter pressure . The vane is connected to and causes rotation of the rotary selector spool inside the selector valve group. 4.SEBV2591 .Drain or reservoir oil Brown . A rotary selector spool (which is connected to the rotary actuator) sends pilot oil to the pressure control valve group to 3. In the larger trucks.Oil supply pressure Red and White Stripes . To initiate a shift. Rotary selector spool 2. a dual stage relief valve limits the maximum system . In this illustration and those that follow. The pump pulls oil through a screen located in the transmission tank and directs the flow to the transmission oil filter. The two sections are transmission scavenge and charging.Charging section The transmission is charged by oil from the second section of the pump. the two section transmission pump (arrow) is mounted on transmission pump the rear of the pump drive which is located inside the left frame near the (arrow) torque converter. .23 - 4/94 20 • Two section On the 769C. the pump is located in a similar position.SEBV2591 . Oil is pulled from the case through a screen and is sent through the transmission oil cooler to the transmission hydraulic tank. . .Scavenge section The first section of the transmission pump is used to scavenge the oil from the bottom of the transmission case. While the larger trucks have more sections. SEBV2591 .24 - 4/94 21 • Transmission oil filter Oil flows from the transmission charging pump through the transmission (arrow) oil filter (arrow). . 3. . pressure tap 4.SEBV2591 .25 - 4/94 4 2 3 1 22 This slide shows the 789B. Downshift solenoid downshift (2) solenoids and the transmission hydraulic controls located under the transmission cover (not shown). The oil eventually falls to the bottom of the transmission case and is scavenged by the first section of the transmission pump. Upshift solenoid Oil flows from the transmission charging filter to the upshift (1) and 2. Transmission pump Transmission pump pressure can be measured at the tap (3). 1. Excess oil flows from the transmission hydraulic controls and lubricates the transmission and transfer gears. Lockup solenoid The lockup solenoid (4) is located on the same manifold as the other solenoids. SEBV2591 . • Rotary selector spool The plug (arrow) can be removed and access to the rotary selector spool is access through plug available for testing and adjusting. the complete valve group can be removed from the transmission case as a unit. If needed. (arrow) .26 - 4/94 23 Access to the selector and pressure control valve on the 793B is permitted by removing the top cover from the transmission. 27 - 4/94 769C .SEBV2591 . Pressure on the downshift side of the rotating vane in the rotary actuator keeps the vane and the rotary selector spool in the NEUTRAL position until a shift is made. Pump flow is blocked at the upshift solenoid and. because the downshift solenoid is continuously energized in NEUTRAL. This condition permits oil to flow to the rotary actuator.37 . The transmission hydraulic system is equipped with a two section gear • Downshift solenoid pump. From the charging section of the pump. the valve in the solenoid is open. the oil flows through the ON in NEUTRAL filter and is sent directly to the two solenoids and the selector valve group. The selector lever must be in the NEUTRAL position to NEUTRAL permit starting the engine. Objective 8 Slides 24 .777C shows the conditions in the system transmission with the ENGINE STARTED and the transmission selector lever in schematic in NEUTRAL.777C TRANSMISSION HYDRAULIC SYSTEM NEUTRAL DOWNSHIFT UPSHIFT PRESSURE PRESSURE A DOWNSHIFT UPSHIFT SOLENOID SOLENOID ROTARY FILTER ACTUATOR E ON PUMP PRESSURE B NEUTRALIZER VALVE PRIORITY ROTARY F PILOT OIL REDUCTION SELECTOR PRESSURE VALVE SPOOL C OIL COOLER CHARGING SCAVENGE PUMP PUMP G D RELIEF VALVE TRANSMISSION H CASE LUBE TANK RELIEF VALVE PRESSURE CONTROL SELECTOR VALVE GROUP GROUP LUBE PRESSURE 24 • Small truck This schematic of the 769C . SEBV2591 . Oil is also sent to the pressure control valve group to fill and engage the station C clutch. From the priority reducing valve. If the oil is cold and thick. the oil flows to the neutralizer valve and to the rotary selector spool. • Excess system oil Excess oil from the transmission pump is directed from the main relief directed to lube valve to the transmission lubrication circuit. This oil is first sent to the priority reducing valve. • Excess case oil All oil that is in the bottom of the transmission case is returned to the tank returned to tank by the transmission scavenge section of the transmission pump. a bypass valve will relieve the excess oil pressure to the transmission case. .28 - 4/94 • Station C clutch is Most of the flow from the charging section of the pump is sent to the engaged selector valve group. 1993 (Form SEPD0184).793B TRANSMISSION HYDRAULIC SYSTEM NEUTRAL UPSHIFT DOWNSHIFT PRESSURE PRESSURE LOCKUP DOWNSHIFT UPSHIFT SOLENOID SOLENOID SOLENOID ROTARY ACTUATOR A ON E TO TORQUE CONVERTER B NEUTRALIZER RELAY VALVE VALVE PRIORITY ROTARY PILOT OIL REDUCTION SELECTOR PRESSURE VALVE SPOOL PUMP F PRESSURE FILTERS C COOLING CHARGING PUMP OIL PUMP SCAVENGE COOLER PUMP G COOLER D BYPASS VALVE H LUBE PRESSURE LOCKUP DUAL STAGE RELIEF VALVE SELECTOR VALVE GROUP PRESSURE CONTROL RELIEF VALVE GROUP TANK LUBRICATION TRANSMISSION CASE RELIEF VALVE 25 • Large trucks in This schematic shows the 785B . 6. For more information about the removal of the valve.29 - 4/94 785B . A shuttle valve is added to the lockup circuit in the selector group. 3. Station D is the lockup dual stage relief valve. 5. The major differences are: • Six major differences 1.SEBV2591 . Six valve stations are used for six speeds FORWARD. . This system has an additional transmission pump section for transmission cooling and lubrication. refer to the Service Magazine article "Transmission Mounted Torque Converter Relay Valve Is No Longer Used" December 6. 2. The lubrication relief valve mounted in the transmission case. INSTRUCTOR NOTE: The transmission mounted torque converter relay valve was removed due to the increased flow capabilities of the lockup solenoid. 4. The lockup solenoid is mounted on a manifold with the upshift and downshift solenoids.793B in the same condition as the NEUTRAL previous schematic. Removal of the threaded cap (5) from the lower left corner of the valve body permits access to the lube relief valve. Rotary actuator bolted to the top of the selector group. 5. Priority reduction the detent springs engage with a detent cam which is pinned to the end of valve the rotary selector spool. Neutralizer valve various chambers are machined in the top of the valve body.SEBV2591 . The rotary actuator (1) is 1. Some of the oil passages which connect the 4. Lube relief valve The small cover (3) at the upper left corner of the valve body permits access to the priority reduction valve. .30 - 4/94 4 3 1 5 2 26 • Selector valve group This view shows the selector valve group. At the opposite 2. Rollers on 3. To the right of the small cover is a larger cover (4) which permits access to the neutralizer valve. The rotating vane in the rotary actuator is directly connected to the rotary selector spool. Detent springs end of the rotary selector spool is a pair of detent springs (2). In the 5. Upper port Two oil ports are located on the outside of the actuator housing. 6.SEBV2591 . Stationary vane body. Pressure oil from the solenoid valves causes the rotating vane and rotary selector spool to turn in either the clockwise or counterclockwise direction. Downshift valve plug Note the position of the plugs that limit the travel of the two valves: The downshift valve plug (7) has a short rod on the plug and the upshift 8. Upshift check valve 7. The stationary vane is bolted to the actuator housing 2. Upshift valve plug valve has a standard plug (8). 3. The upper port (3) is for pressure oil from the downshift solenoid and the 4.31 - 4/94 1 3 7 5 2 4 6 8 27 • Rotary actuator Shown is the rotary actuator after the removal from the selector valve 1. Lower port lower port (4) is for pressure oil from the upshift solenoid. Inside the actuator housing are a stationary vane (1) and a rotating vane (2). Downshift check respective oil passages to the rotary vane are a downshift (5) and upshift valve (6) valve (check valves) that cover and uncover a drain passage. . Rotating vane and the rotating vane is pinned to the rotary selector spool in the center of the housing. When the shift is indicated. To shift from NEUTRAL to any other gear. Any oil that was in the chamber on the nonpressurized (downshift) side of the vane is forced out of the chamber by the movement of the vane. the rotating vane must turn in the clockwise direction to the selected • Upshifts .SEBV2591 . • Downshifts . As the oil flows out of the chamber.clockwise gear position. The pressure oil then flows through the check valve and fills the small space between the two vanes. direction . This movement opens a drain passage located near the inner end of the upper check valve passage and permits the oil to flow out of the center chamber. it moves the upper check valve away from the center of the actuator housing.32 - 4/94 • Rotary actuator in This view of the rotary actuator vane shows the vane in the NEUTRAL NEUTRAL position (fully counterclockwise). As the pressure increases. the rotating vane moves in the clockwise direction to the appropriate gear position. This sequence is just the opposite for downshifts (when the rotating vane counterclockwise moves in the counterclockwise direction). The pressure oil moves the check valve toward the center of the actuator housing until the check valve covers a drain passage located near the inner end of the inlet passage. pressure oil from the upshift direction solenoid is sent to the lower inlet port (4). 2 . the rotating vane has moved a small distance in the speed clockwise direction. This is the approximate position for FIRST.6 . When the rotary spool gets to FIRST. the N1 clutch remains engaged in the N2 position and then changes to another clutch in FIRST.1 . The upshift sequence in the spool 777C to 793B trucks is N1 .7.R .SEBV2591 .4 . In the 785B and 793B trucks. the N2 clutch stays engaged and another clutch is engaged to complete the power flow path to the wheels. The • 777C .793B have N2 clockwise sequence for upshifts at the rotary actuator in the 769C and position on rotary 773B trucks is N .1 .6 .4 .2 .7 (785B and 793B have only six speeds FORWARD).N2 . In the 777C. .3 .3 .33 - 4/94 28 • Rotary vane in FIRST In this view.5 . the N1 clutch drops out and in N2 another clutch is engaged momentarily to slow the rotation of the internal mass of the planetaries. as the rotary actuator moves the rotary spool from N1 to N2 past REVERSE to FIRST.R .5 . 3.SEBV2591 . A bolt and flat washer (3) help to retain 2. The detent cam is installed in the end of the rotary selector spool and turns with the spool.34 - 4/94 1 2 3 4 29 • End of rotary selector This close view shows the end of the selector valve group opposite the spool rotary actuator. Bolt and flat washer 4. Springs the rotary selector spool in the valve body. Pins in the support block and flat retainers help to align the detent springs and hold them in position. NOTE: The support block (4) is notched where the bolts mount the block to the housing to allow adjustment of the detent springs. Support block The detent springs are bolted to a support block (4) which is part of the access cover for the main relief valve. . Detent cam springs (2). Visible in this view are the detent cam (1) and the detent 1. . pilot oil from the upper chamber (indicated by the red arrow) is directed to the pressure control valve group to initiate clutch engagement. . For N1 and N2. A plug and . only one outlet port permits pilot oil to flow to the pressure control valve group.35 - 4/94 30 • Rotary selector spool The rotary selector spool is actually a hollow rotating shaft. two of the outlet ports from the upper chamber are aligned with drilled passages in the selector valve body. the lower half of the spool blocks the drain passage to that station. all but two of the drain ports are open to drain.Selects clutch combinations During operation. Whenever a clutch station is engaged. The lower chamber in the rotary selector spool is always open to drain (as indicated by the green arrow). For each gear position except N1 and N2. For any gear except NEUTRAL (N1 and N2).Contains plug and screen assembly inside the spool divides the center cavity into two screen assembly separate oil chambers.SEBV2591 . The screen should be inspected and cleaned whenever the selector valve group is disassembled. The screen prevents assembly plugging or restriction of the outlet ports from the upper chamber by removing particles of dirt or foreign material from the pilot oil. .36 - 4/94 31 • Rotary selector spool Removal of the pin and dent cam from the end of the rotary selector spool plug and screen permits access to the plug and screen assembly.SEBV2591 . SEBV2591 . the rotary selector spool has been cut in half to show how the cut in half plug and screen assembly divides the center cavity into two separate oil chambers. notice how the screen fits inside the upper chamber (on the right). The oil then flows into the open end of the screen and through the screen mesh to the outlet ports.37 - 4/94 32 • Rotary selector spool In this view. Also. . Pilot oil enters the upper chamber through the passage at the end of the screen. 777C TRANSMISSION SELECTOR VALVE GROUP NEUTRAL ROTARY SELECTOR NEUTRALIZER SPOOL VALVE PRIORITY REDUCTION VALVE PILOT OIL PRESSURE SCREEN RELIEF VALVE LUBE RELIEF VALVE LUBRICATION PRESSURE 33 • Selector valve group This schematic shows the 769C . the neutralizer valve directs pilot oil to the center of the rotary selector spool. .SEBV2591 . • Neutralizer valve The neutralizer valve moves only when the rotary selector spool is in the NEUTRAL position. flows up around the check ball.777C selector valve group during in NEUTRAL operation in NEUTRAL. If the rotary selector spool is not in the NEUTRAL position during engine start-up. pump oil flows through a passage in the center of the neutralizer valve.38 - 4/94 769C . The priority reducing valve is installed in the • Priority reducing valve bore on the left side of the valve body. In this position. When the rotary selector spool is in the NEUTRAL position and the engine is started. the neutralizer valve will block the flow of pilot oil to the rotary selector spool. This valve has two functions: It controls the pressure of the pilot oil (orange) that is used to initiate clutch engagement. pressurizes the top of the valve. and then moves down. and it makes sure that pilot pressure is available at the neutralizer valve before pressure oil (red) is sent to the remainder of the system. SEBV2591 . Excess pump oil • Lube relief valve is directed to the lubrication circuit and the pressure is maintained by the lube relief valve. the rotary selector spool directs pilot oil to one station for clutch engaged the engagement of only one clutch. one In NEUTRAL.39 - 4/94 • Main relief valve Directly below the neutralizer valve is the main relief valve. Check the appropriate service manual for which stations control specific clutches. This valve limits the maximum system pressure during operation. • In NEUTRAL. • Rotary selector spool The rotary selector spool is installed in the bore on the right side of the valve body. . When the lockup solenoid is energized. oil from the solenoid to valve • Station D reduces station D must flow through the shuttle valve.793B TRANSMISSION SELECTOR VALVE GROUP NEUTRAL SHUTTLE VALVE PRIORITY NEUTRALIZER REDUCTION VALVE ROTARY VALVE SELECTOR SPOOL PILOT OIL PRESSURE SCREEN RELIEF VALVE ORIFICE PLUGS 34 • Larger truck selector The 785B . • Shuttle valve in lockup circuit Just above and to the right of the neutralizer valve is a shuttle valve. The reduced pressure in direct drive is controlled by valve station D in the pressure control valve group. pump oil pressure (red) stops and the oil in station D can quickly flow to drain through the uncovered drain passage opened by the shuttle valve.793B trucks have a slightly different selector valve group. Each time the lockup system pressure in converter drive solenoid is de-energized. . valve group The main relief valve is now a dual stage relief valve and has two • Two function main functions: It limits the maximum system pressure during converter drive relief valve and provides a reduced system pressure for direct drive. • Lube relief valve replaced by plug The lube relief valve is replaced by a plug.40 - 4/94 785B .SEBV2591 . The neutralizer cannot move down to allow pilot oil to the center of the rotary selector spool.SEBV2591 . . the spool stops the transmission pump oil (see purple arrow) from entering the side passage of the neutralizer valve.777C TRANSMISSION SELECTOR VALVE GROUP STARTING IN FIRST SPEED FORWARD ROTARY SELECTOR NEUTRALIZER SPOOL VALVE PRIORITY REDUCTION VALVE PILOT OIL PRESSURE SCREEN RELIEF VALVE LUBE RELIEF VALVE LUBRICATION PRESSURE 35 • Oil blocked by rotary If the transmission is started with the rotary selector spool in a position selector spool other than NEUTRAL.41 - 4/94 769C . The stations are as follows: 1. B 3. E 6. station D is the dual stage relief valve. The identification letters for the valve stations are stamped on the inside covers top cover plate and on the ends of the seven outer covers (stations). G 8. H .) 5. (stations) This view shows a typical pressure control valve group.SEBV2591 . A 2. C 4. On the larger trucks. F 7.42 - 4/94 7 8 5 6 4 3 2 1 36 • Seven modulation The pressure control valve group contains seven modulation reduction reduction valves valves. D (Plugged on the small trucks. 777C PRESSURE CONTROL GROUP F NEUTRAL C G D H PRESSURE CONTROL GROUP 37 • Pressure control This schematic shows the pressure control group in NEUTRAL. .SEBV2591 . Modulation of the clutch pressure began when pilot oil from the rotary selector spool was sent to the outer end of the selector piston in station C. Initial movement of the selector piston must take place before modulation can begin.43 - 4/94 A E B 769C . but • Clutch C engaged only the station C clutch is engaged. Notice group in NEUTRAL that pressure oil is available at all of the modulation reducing valves. Both the selector piston and the load piston were moved by pilot oil pressure and the load piston was moved during modulation by clutch pressure (red and white stripes). 46 .SEBV2591 . an same basic explanation of the operation of one station can be applied to the operation components of the remaining six stations (including the lockup clutch station).44 - 4/94 VALVE STATION SLUG BALL CHECK VALVE CLUTCH RELEASED LOAD PISTON SELECTOR PISTON PILOT OIL PASSAGE PLUG DECAY ORIFICE LOAD PISTON LOAD PISTON PLUG MODULATION ORIFICE REDUCTION VALVE CLUTCH PRESSURE TAP FROM PUMP TO CLUTCH 38 • All stations contain Since all seven valve stations contain the same basic components. Components that are identical for all seven stations include: • Modulation reduction valve • Ball check valve • Load piston • Selector piston • Decay orifice • Load piston plug • Plug • Load piston orifice • Clutch pressure tap Objective 11 Slides 38 . The retaining springs for the load piston orifices are identical. station D is the dual stage relief valve and does not contain an orifice. until pilot oil from the rotary selector spool is sent to the right (outer) end of the selector piston. pump (or system) pressure is always available at the modulation reduction valve spool.SEBV2591 . Many of the stations are equipped with decay orifices. but the orifices vary in thickness from one station to another. but.45 - 4/94 • Load piston orifices The six stations that control the clutches contain load piston orifices control modulation (sometimes called "cascade" orifices). . there can be no valve movement and the clutch cannot be engaged. the engine has been started. but the clutch for this selected station has not been engaged. • Station has not been In this schematic. While the engine is running. Check the parts book for proper component placement. In the larger trucks. Station D has a stations A to D plug. B.46 - 4/94 39 • Components in This view shows the components in stations A. Each station has similar components except the load piston springs. . and C.SEBV2591 . shims and orifices may be different. Seal orifice. Reduction valve counterbore in the side of the valve body and the load piston springs pass spool through the center of the stop. Orifice position by the retaining spring (7). Stop The load piston orifice (6) fits in a bore in the outer cover and is held in 6. 5 in components: a 777C. The stop (5) fits in a 4. Spring between the orifice and the end of the bore to prevent leakage around the 8. 1. clutch No.47 - 4/94 4 3 5 8 7 1 2 6 40 • Station E This close view shows the valve components for station E. Selector piston the load piston springs (3) fit inside the load piston and the bore in the end 3. Springs of the modulation reduction valve spool (4). An o-ring seal (8) is installed 7. Load piston Notice that the load piston (1) fits inside the selector piston (2) and that 2. .SEBV2591 . 5. SEBV2591 - 48 - 4/94 41 • Load piston orifice cut An extremely close view of two load piston orifices shows how they are in half different from other designs. The orifice on the right is complete and the orifice on the left has been cut in half. (The sectioned orifice was mounted in plastic to prevent collapsing of the internal passages while it was cut and the complete orifice was placed on a plastic pedestal for photographic purposes.) What makes this type of orifice different is that the oil must enter a hole • Oil flows through labyrinth to load in the face of the orifice and flow through an intricate internal passage piston before it can flow out of a second hole in the opposite face. An internal passage of this type is often referred to as a "labyrinth." Cascade orifices are used in applications where a very small conventional or "straight- through" orifice could easily become plugged. Cascade orifices provide the same pressure drop and time delay as small conventional orifices, but utilize larger holes and passages. Also, cascade orifices are not as sensitive to changes in temperature as small conventional orifices. SEBV2591 - 49 - 4/94 VALVE STATION CLUTCH FILLING LOAD PISTON ORIFICE 42 • Station showing This schematic shows the relative positions of the valve station beginning of components at the start of modulation before the clutch is fully engaged modulation (primary pressure). Valve movement is initiated when pilot oil from the • Selector spool rotary selector spool moves the selector piston to the left as shown. movement begins Movement of the selector piston accomplishes two purposes: modulation 1. The drain passage at the decay orifice is blocked. 2. The load piston springs are compressed. • Clutch pressure Compressing the load piston springs moves the reduction valve spool to increases the left against the force of the inner spring. This movement opens the supply passage (from the pump) and permits pressure oil to flow to the clutch. As the clutch fills, pressure oil opens the ball check valve and fills the slug chamber at the left end of the reduction valve spool. At the same time, oil flows through the load piston orifice and fills the chamber between the end of the load piston and the selector piston. The load piston orifice provides a pressure drop and time delay in the flow of oil to the load piston chamber. This condition helps control the rate of modulation. Filling the load piston chamber is made possible when the selector piston covers the drain passage at the decay orifice. SEBV2591 - 50 - 4/94 • Clutch pressure The clutch pressure and the pressure in the slug chamber increase at the maintained by same rate. Just after the clutch is filled, the pressure in the slug chamber reduction valve moves the reduction valve to the right. This movement restricts the flow of pressure oil to the clutch and briefly limits the increase of clutch pressure. The pressure in the load piston chamber then moves the load piston farther to the left. This movement increases the spring force and reopens the supply passage permitting the clutch pressure to again increase. This cycle continues until the load piston has moved completely to the left (against the stop). The clutch pressure is then at its maximum setting. During modulation, the reduction valve spool moves left and right while the load piston moves smoothly to the left. . As clutch leakage occurs. This is the "metering position" of the reduction valve spool. At the end of the modulation cycle. the valve maintains precise control of the clutch pressure. At this point. an engaged clutch is designed to leak a relatively small leak small amount but steady volume of oil. Because this is a modulation reduction valve. Pressure oil from the pump again enters the clutch circuit and replaces the leakage. the pressure in the slug chamber moves the reduction valve a small distance to the right to restrict the flow of supply oil to the clutch. the clutch pressure in the slug chamber moves the spool back to the right thereby restricting the flow of supply oil to the clutch.51 - 4/94 VALVE STATION CLUTCH ENGAGED 43 • Modulation cycle The load piston has now moved completely to the left against the stop. • Clutch designed to During operation. In this position. This leakage helps prevent high oil temperatures and provides additional lubrication for the planetary gears and bearings. Then. the maximum pressure setting of the clutch is lower than the system pressure. completed The modulation cycle is completed and the clutch pressure is at its maximum setting. the load piston springs move the reduction valve spool a small distance to the left to open the supply passage. This metering action continues during the entire time that the clutch is engaged.SEBV2591 . the clutch pressure and the pressure of the oil in the slug chamber will start to decrease. During the time that the clutch is engaged. As a result. Near the end of the modulation cycle. and opens the clutch passage to supply oil. supply oil is always available at the clutch. Replacement of clutch leakage for these stations requires no additional valve movement because the pin holds the reduction valve spool in the open position. The difference is caused by a pin in the center of the load piston springs. the reduction valve spool remains completely to the left and the clutch pressure is equal to the system pressure.SEBV2591 . At this point. .52 - 4/94 VALVE STATION CLUTCH ENGAGED/WITH PIN 44 • Some stations may The operation of some clutch stations is slightly different than the have pin operation of the other stations. the pin contacts the reduction valve spool. moves the spool completely to the left. modulation ends and the clutch pressure immediately increases to maximum. The only way that oil can flow out of this chamber is through the decay orifice which was uncovered when the selector piston moved to the right. When the load piston has moved completely to the right. . the clutch pressure gradually decreases. Instead. Restricting the rate of clutch pressure decay helps to maintain a positive torque at the transmission output shaft.53 - 4/94 VALVE STATION CLUTCH DECAY DECAY ORIFICE 45 • Clutch pressure During a shift. the chamber at the right (outer) end of the selector piston is opened to drain through the lower chamber in the rotary • Decay orifice controls selector spool. When a clutch is released. the clutch pressure decreases at a controlled rate controlled rate. the pressure of the clutch (or clutches) being released does decreases at not immediately drop to zero. This condition permits the selector piston and load piston rate of clutch pressure decrease to move to the right as shown. but cannot drop to zero until the chamber between the load piston and the selector piston is drained. Clutch pressure starts to decrease. An immediate drop in clutch pressure would permit a rapid deceleration of the power train components that remain connected to the differential during a shift. the clutch pressure is zero. As the load piston springs force the oil from the load piston chamber. This feature minimizes the effects of tire and axle "unwinding" and permits smoother shifts.SEBV2591 . green (2) is 1.).54 - 4/94 3 2 1 46 • Decay orifices are The decay orifices are identified by a color code.047 in.055 in. The colors designate color coded the hole size of the orifice--yellow (1) is 1. and blue (not shown) is 1.SEBV2591 . The green and red orifices are made of steel while the yellow and blue orifices are plastic.).57 mm (. .). The plastic orifices are equipped with a small screen to help prevent restriction of their relatively small hole diameters.078 in. Consult the parts book for the specific placement of any component. red (3) is 1. NOTE: Some stations may not have a decay orifice.19 mm (.98 mm (.40 mm (.).062 in. NOTE: The position of the rotary actuator vane in the 769C and 773B trucks would be one position counterclockwise because these machines do not have an N2 position. The upshift trucks solenoid is energized and directs pump oil to the rotary actuator.777C. The 777C has the N2 position. The rotary actuator moves the rotary selector spool to the THIRD SPEED FORWARD position. The rotary spool selects two stations (C and E) which modulate the two clutches. .SEBV2591 .55 - 4/94 769C .777C TRANSMISSION HYDRAULIC SYSTEM THIRD SPEED FORWARD UPSHIFT DOWNSHIFT PRESSURE PRESSURE A DOWNSHIFT UPSHIFT SOLENOID SOLENOID ROTARY FILTER ACTUATOR E PUMP PRESSURE B 3 NEUTRALIZER VALVE N1 PRIORITY ROTARY F PILOT OIL REDUCTION SELECTOR PRESSURE VALVE SPOOL C OIL COOLER CHARGING SCAVENGE PUMP PUMP G D RELIEF VALVE TRANSMISSION H CASE LUBE TANK RELIEF VALVE PRESSURE CONTROL SELECTOR VALVE GROUP GROUP LUBE PRESSURE 47 • Third speed This schematic shows the components and the oil flow in the system FORWARD for small during operation in THIRD GEAR for the 769C . Clutches No. 1 and 5 are selected and the load piston orifices are controlling their engagement. 3 and 6 are being gradually released by the controlling effect of the decay orifices.SEBV2591 .56 - 4/94 777C SHIFT MODULATION CYCLE THIRD TO FOURTH PRESSURE NORMAL SHIFT CYCLE CLUTCH 1 418 CLUTCH 6 373 CLUTCH 5 353 CLUTCH 3 265 COMPLETE CLUTCH ENGAGEMENT PRIMARY PRESSURE INITIAL CLUTCH ENGAGEMENT 50 0 TIME FILL TIME NORMAL CLUTCH SLIP 48 • Modulation cycle of This graph shows the clutch pressures as the ground speed increases and clutches the transmission shifts into higher gears. clutches No. At a certain point. . SEBV2591 . Clutch No. This feature helps to minimize the unwinding motion of the power train.57 - 4/94 777C SHIFT MODULATION CYCLE SECOND TO THIRD PRESSURE NORMAL SHIFT CYCLE CLUTCH 3 418 373 CLUTCH 6 CLUTCH 1 265 COMPLETE CLUTCH ENGAGEMENT PRIMARY PRESSURE INITIAL CLUTCH ENGAGEMENT 80 0 TIME FILL TIME NORMAL CLUTCH SLIP 49 • Some shifts change This graph shows the clutch pressures when a shift is made from only one clutch SECOND to THIRD. 6 does not release. . Maximum clutch pressure is also lower and may cause slippage during conditions of heavy loading. High primary pressure 1.58 - 4/94 PRESSURE RESTRICTED LOAD PISTON ORIFICE SLOW MODULATION HIGH PRIMARY PRESSURE P1 COMPLETE CLUTCH ENGAGEMENT LOW PRIMARY PRESSURE INITIAL CLUTCH ENGAGEMENT NORMAL PRIMARY PRESSURE 0 TIME HIGH PRIMARY PRESSURE .This effect is very similar to the low primary pressure.CLUTCH SLIPPING RESTRICTED LOAD PISTON ORIFICE CLUTCH SLIPPING 50 • Three shift conditions: This graph shows the effects of the following conditions: 1. 3. Slow modulation . Slow modulation 2. 3. The maximum clutch pressure would be within specifications.Shorter engagement time which causes harsh shifts of the power train components and increases the 2. Low primary pressure maximum clutch pressure.Longer engagement time which causes the plates and discs to slip more before the engagement pressure holds them together. High primary pressure . but it can be caused by a partially plugged load piston orifice.SEBV2591 . .HARSH SHIFT NORMAL CLUTCH SLIP SHIFT MODULATION PROBLEMS LOW PRIMARY PRESSURE . Low primary pressure . Transmission oil flow moves the torque converter mounted relay valve which begins the 2. Station D sends reduced pressure oil through an orifice at the right of the dual stage relief valve to the chamber at the bottom of the relief valve and the main system pressure is reduced. 1. .793B trucks: trucks. station D 3. pressure setting 3. Oil directed to engagement of the torque converter lockup clutch. Lockup clutch energized 1. Oil from the lockup solenoid is also sent through the shuttle valve valve at lower at the right of the neutralizer valve to station D.793B TRANSMISSION HYDRAULIC SYSTEM THIRD SPEED FORWARD UPSHIFT DOWNSHIFT PRESSURE PRESSURE LOCKUP DOWNSHIFT UPSHIFT SOLENOID SOLENOID SOLENOID ROTARY ACTUATOR A ON 3 E N1 TO TORQUE CONVERTER B NEUTRALIZER RELAY VALVE VALVE PRIORITY ROTARY PILOT OIL REDUCTION PRESSURE SELECTOR VALVE SPOOL PUMP F PRESSURE FILTERS C COOLING PUMP SCAVENGE OIL CHARGING COOLER PUMP PUMP G COOLER D BYPASS VALVE H LUBE PRESSURE LOCKUP DUAL STAGE RELIEF VALVE SELECTOR VALVE GROUP PRESSURE CONTROL RELIEF VALVE GROUP TANK LUBRICATION TRANSMISSION CASE RELIEF VALVE 51 • Third speed This schematic shows the components and the oil flow in the system FORWARD for large during operation in THIRD SPEED FORWARD in the 785B .SEBV2591 . Dual stage relief 2. The lockup solenoid is energized.59 - 4/94 785B . The upper (supply) orifice has a larger hole size than the lower (drain) orifice. This flow moves the shuttle valve down to cover the small drain hole at the right side of the valve. When the machine shifts from direct drive to converter drive.793B TRANSMISSION HYDRAULIC SYSTEM THIRD SPEED FORWARD SCREEN RELIEF VALVE SELECTOR VALVE GROUP LOWER ORIFICE UPPER ORIFICE 52 • Lockup in larger In the large trucks.SEBV2591 . Therefore. the selector piston chamber for station D is drained at the shuttle valve. When changing from direct to converter drive. the oil in the chamber at the bottom of the spool is drained through the lower orifice. Just below and to the right of the dual stage relief valve are two orifices. In direct drive.60 - 4/94 SHUTTLE VALVE NEUTRALIZER PRIORITY VALVE ROTARY REDUCTION SELECTOR PILOT OIL VALVE SPOOL PRESSURE 785B . With a larger effective area. a lower system pressure is required to overcome the spring force and open the relief valve. Pressure oil can then flow to station D and fill the chamber at the end of the selector piston. . oil from station D flows through the upper orifice and fills the chamber at the lower end of the dual stage relief valve spool. flow from the lockup solenoid enters the selector valve trucks explained group at the right of the neutralizer valve. The pressure of this oil works against the end of the spool thereby increasing the effective reaction area of the relief valve. the system pressure in direct drive is lower than the system pressure in converter drive. Because station D does not contain a load piston orifice and a decay orifice.61 - 4/94 A E B 785B . while valve movement in station D is initiated by pressure oil from the lockup solenoid. Valve movement in stations C and E is initiated by pilot oil from the rotary selector spool. the pressure rise and pressure drop controlled by this station occur very rapidly. a pressure gauge connected at each station will show the clutch pressure for each gear range as the transmission is manually upshifted and downshifted. Since each clutch has its own modulation reduction valve. . Stations C and E control the operation of their respective clutches. The overall design of the pressure control valve group permits a relatively • Clutch pressures easily checked easy check of the clutch pressures.SEBV2591 .793B PRESSURE CONTROL GROUP THIRD SPEED FORWARD F C G D H LOCKUP DUAL STAGE RELIEF VALVE PRESSURE CONTROL GROUP 53 • Stations C and E This schematic shows the components and the oil flow in the pressure engaged in pressure control valve during operation in THIRD SPEED FORWARD in the large control valve trucks. The slow . the chamber between the end of the load piston and the selector piston is opened to drain. rough shifts that can result in damage to the power train. . High primary pressure settings will cause fast. This condition prevents the clutch pressure from increasing above its primary pressure setting. but they can cause decreased clutch life due to excessive clutch slippage. Introduce and perform INSTRUCTOR NOTE: At this time.rough shifts they control clutch phasing and fill times.slow shifts shifts will often be smooth. • Low primary pressure Low primary pressure settings will cause slow or delayed shifts. I. These shop lab and classroom exercises will reinforce the material introduced in the preceding slide presentation. • High primary pressure Correct adjustment of the primary pressures is very important because . When the load piston (inner) plug is removed from plug the valve station cover.SEBV2591 . I. G. and J H.62 - 4/94 VALVE STATION PRIMARY PRESSURE LOAD PISTON PLUG (REMOVED) 54 • Primary pressure This schematic shows the conditions present when the clutch primary checked by removing pressures are checked. G. Labs F. introduce and perform Labs F. H. and J. SEBV2591 .Third to Fourth Schematic (section) (section) 16. Large Truck Selector Valve In Neutral (section) 35. Large Truck in Lockup (section) 19. 777C Torque Converter Pump (iron) 43. Large Truck Transmission Schematic in Third 18. Station E Components (iron) 7. Small Truck Pressure Control Group in Neutral 3. Stations (iron) 6. Decay Orifices Color Codes (iron) 13. Station Components (section) 5. Station at Primary Pressure (section) 22. Large Truck Torque Converter Hydraulic Speed FORWARD (section) Schematic (section) 52. Transmission Components (iron) 23. Selector Valve (iron) 27. Rotary Actuator (iron) 28. 777C Shift Modulation Graph . Torque Converter In Direct Drive (section) 39. Small Truck Transmission Schematic in Third 14. Station with Pin (section) 11. Small Truck Torque Converter Hydraulic 48. Station Decay (section) 12. Torque Converter Components (iron) 42. Large Truck Torque Converter Hydraulic 50. Transmission Oil Filter 54.63 - 4/94 SLIDE LIST 1. Pressure Control Valve Stations (iron) 2. Large Truck Pressure Control in Third Speed 20. Transmission Pump (iron) FORWARD (section) 21. Small Truck Rotary Selector Spoon not in Neutral (section) . Torque Converter Lockup Clutch (section) 46. Rotary Selector Spool (iron) 31. Torque Converter Components (iron) (section) 4. Parking Brake Release Filter 44. Small Truck Selector Valve In Neutral (section) 34. 777C Shift Modulation Graph . Station at Beginning of Modulation (section) 9. Large Truck Torque Converter Hydraulic 49. Torque Converter In Converter Drive (section) 38. Lockup Clutch Filling (section) 47. Small Truck Transmission Hydraulic Schematic (section) 25. Station at End of Modulation (section) 10. Torque Converter Pump (iron) 40. Large Truck Transmission Hydraulic Schematic (section) 26.Second to Schematic In Torque Converter Drive (section) Third (section) 17. Rotary Actuator in First Speed (iron) 29. 777C Torque Converter Components (iron) 45. Torque Converter Components (iron) 41. Rotary Selector Spool (iron) 30. Transmission Control Valve 53. Load Piston Orifice (iron) 8. Shift Modulation Problems (section) Schematic In Direct Drive (section) 51. Rotary Selector Spool Screen and Plug (iron) 32. Rotary Selector Spool Sectioned (iron) 33. Selector and Pressure Control Valve (iron) 24. Lockup Clutch Engaged (section) Speed FORWARD (section) 15. Model View 36. Top and Side View (section) 37.