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| Illustration 1 | g00679222 |
Hydraulic System Schematic (1) Transmission oil filter (2) Transmission hydraulic control relief valve (3) Torque converter inlet relief valve (4) Torque converter priority valve (5) Torque converter outlet relief valve (6) Torque converter (7) Modulating valve for the lockup clutch (8) Power train oil pump (9) Modulating valve for the impeller clutch (10) Power train oil cooler (11) Modulating valve for number 1 clutch (12) Modulating valve for number 4 clutch (13) Modulating valve for number 2 clutch (14) Modulating valve for number 5 clutch (15) Modulating valve for number 3 clutch (16) Modulating valve for number 6 clutch (17) Lubrication of the transmission planetary (18) Suction screen and magnet (19) Oil sump (20) Lubrication of the input transfer gears (A) Torque converter inlet pressure tap (B) Pressure tap for pump pressure (C) Pressure tap for the modulating valve (lockup clutch) (D) Torque converter outlet pressure tap (E) Pressure tap for the modulating valve (impeller clutch) | |
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| Illustration 2 | g00614519 |
988G Wheel Loader Torque Converter Cover (C) Pressure tap for lockup clutch (lockup clutch is optional on the 988G) (E) Pressure tap for impeller clutch | |
| NOTICE |
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Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids. Refer to Special Publication, NENG2500, "Caterpillar Tools and Shop Products Guide" for tools and supplies suitable to collect and contain fluids on Caterpillar products. Dispose of all fluids according to local regulations and mandates. |
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Personal injury or death can result from sudden machine movement. Sudden movement of the machine can cause injury to persons on or near the machine. Prevent possible injury by performing the procedure that follows before working on the machine. |
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- Park the machine on a smooth level surface.
- Shift the transmission direction control to the NEUTRAL position.
- Lower the bucket or the work tool to the ground. Lower the blade or the work tool to the ground.
- Engage the parking brake.
- Place blocks in front of the wheels and behind the wheels.
- Allow only authorized personnel on the machine. Keep unauthorized personnel off the machine and in clear sight of the operator.
Note: All tests and all adjustments must be made while the transmission oil is at normal operating temperature.
| NOTICE |
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Do not connect or disconnect hose fittings to or from the quick disconnect nipples when there is pressure in the system. This will prevent damage to the seals that are in the fitting. |
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| Illustration 3 | g00618748 |
Outlet Relief Valve (5) Torque converter outlet relief valve (20) Spacers | |
| Torque Converter Pressure | |||
| Pressure | Pressure Tap | Pressure at High Idle | Adjustment |
| Lockup Clutch | (C) | Stabilized pressure with an activated solenoid is 1720 ± 70 kPa (250 ± 10 psi). Pressure is 0 psi when the solenoid is not activated. |
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| Torque Converter Inlet P3 | (A) | Maximum pressure with cold oil is 1025 kPa (149 psi). |
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| Impeller Clutch | (E) | 834G Wheel Tractor The impeller clutch top pressure must be a minimum of 1650 kPa (240 psi). Pressure with the left brake pedal fully depressed is 235 ± 150 kPa (34 ± 22 psi). |
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| 836G Landfill Compactor The impeller clutch top pressure must be a minimum of 1650 kPa (240 psi). Pressure with the left brake pedal fully depressed is 165 ± 150 kPa (24 ± 22 psi). |
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| Torque Converter Outlet | (D) | Maximum pressure at high idle is 415 kPa (60 psi). Minimum pressure at low idle is 370 kPa (54 psi). (These pressures are for a machine in third speed, with activated brakes, with installed axle shafts, and with the converter in a stall condition.) |
Add spacers (20) or remove spacers (20). |
| Pressure Change for One Spacer (1) | |||
| Description | Thickness | Pressure Change | Part |
| 5M-9622 Spacer | 1.60 mm (.063 inch) |
32.6 kPa (4.73 psi) |
Output Relief Valve (5) |
| 5M-9623 Spacer | 0.91 mm (.036 inch) |
18.6 kPa (2.70 psi) |
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| 5M-9624 Spacer | 0.25 mm (.010 inch) |
5.1 kPa (.74 psi) |
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| ( 1 ) | Before an adjustment is made to outlet relief valve (15), make sure that the valve springs are not weak or broken. |
| Required Tools | ||
| Part Number | Description | Quantity |
| 1U-5481 (1) | Pressure Gauge Group | 1 |
| 1U-5482 | Pressure Adapter Group | 1 |
| 4C-8195 | Control Service Tool | 1 |
| 7X-1701 | Communication Adapter | 1 |
| ( 1 ) | The 198-4240 Pressure Indicator Tool Gp is also available. |
Lockup Clutch Disengaged (Minimum Clutch Pressure)
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The drive shaft rotates between the torque converter and the transmission whenever the engine is running. Contact with the rotating shaft can result in personal injury or death. The rotating shaft is located under the implement and steering pumps. Do not allow personnel into the pump bay area behind the cab when the engine is running. |
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Personal injury or death can result from sudden machine movement. Sudden movement of the machine can cause injury to persons on or near the machine. To prevent injury or death, make sure that the area around the machine is clear of personnel and obstructions before operating the machine. |
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- Install a hose and a 4130 kPa (600 psi) pressure gauge on pressure tap (C) .
- Engage the parking brake and shift the transmission direction control to the NEUTRAL position. Start the engine and run the engine at high idle.
- Observe the pressure gauge. The pressure reading on the gauge should be 0 kPa (0 psi).
Lockup Clutch Engaged (Maximum Stabilized Pressure)
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The drive shaft rotates between the torque converter and the transmission whenever the engine is running. Contact with the rotating shaft can result in personal injury or death. The rotating shaft is located under the implement and steering pumps. Do not allow personnel into the pump bay area behind the cab when the engine is running. |
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Personal injury or death can result from sudden machine movement. Sudden movement of the machine can cause injury to persons on or near the machine. To prevent injury or death, make sure that the area around the machine is clear of personnel and obstructions before operating the machine. |
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- Install a hose and a 4130 kPa (600 psi) pressure gauge on pressure tap (C) .
- Move the on/off switch for the lockup clutch to the ON position by depressing the top of the switch.
- Engage the parking brake and place the transmission direction control in the NEUTRAL position. Start the engine.
- Apply the service brakes and release the parking brake. Shift the machine into the FIRST SPEED FORWARD position.
- Operate the machine at maximum speed and observe the pressure reading on the gauge. Make sure that the left service brake pedal and the right service brake pedal is not depressed. If the service brake pedal is depressed the lockup clutch will not engage. The maximum stabilized pressure must be 1720 ± 70 kPa (250 ± 10 psi).