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Personal injury or death can result from sudden machine movement. Sudden movement of the machine or release of air pressure or oil pressure can cause injury to persons on or near the machine. To help prevent possible injury before testing and adjusting any air system or hydraulic system, perform the procedure in the Testing and Adjusting, "General Information" section. |
Perform the checks before you troubleshoot a problem. Make sure that the transmission is in neutral and stop the engine. During the checks, use a magnet to separate ferrous particles (iron and steel) from nonferrous particles (aluminum, rubber and bronze).
Check: Check the oil level in the hydraulic tank.
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| Illustration 1 | g00313883 |
| (1) Torque converter and front brake cooling oil cooler | |
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| Illustration 2 | g00352772 |
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(2) Rear brake oil coolers
(3) Screens for the rear brake oil coolers | |
Check the oil level in the hydraulic tank. Look for air or water in the sight gauge. Many problems in the torque converter are caused by low oil level or air in the oil. Add oil to the hydraulic tank, if necessary. See the Operation and Maintenance Manual for the correct type of oil.
Problem: There is an indication of water in the oil.
Probable Cause
- Failure of torque converter and front brake cooling oil cooler (1)
- Failure of the rear brake oil coolers (2)
Problem: There is an indication of air in the oil.
Probable Cause
- There is a leakage in the oil lines. See "Check: Check for oil leakage.".
Problem: The oil level is too low.
Probable Cause
- There is a leakage in the oil lines. See "Check: Check for oil leakage.". Add oil before you perform any tests.
- Brake cooling oil has leaked into the final drives. Check oil level in each final drive.
Problem: The oil level is too high.
Probable Cause
- The engine crankshaft rear seal is allowing engine oil into the torque converter housing.
Inspect all oil lines, all hoses and all connections for damage or for leaks. Look for oil on the ground under the machine.
Note: If oil can leak out of a fitting or out of a connection, air can enter the system. Air in the system can be as harmful as having too little oil.
Check: Check the parking brake release hydraulic filter.
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| Illustration 3 | g00482616 |
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(6) Parking brake release hydraulic filter
(23) Bypass switch | |
Remove parking brake release hydraulic filter (6). Inspect parking brake release hydraulic filter (6) for foreign material. Cut the filter open, if necessary.
Note: Parking brake release hydraulic filter (6) has an oil bypass valve. The bypass valve allows the oil to bypass the oil filter element or the screen whenever the pressure difference between the inlet oil and the outlet oil becomes too high. Any oil that does not flow through the filter element or through the screen goes directly into the hydraulic circuit. Dirty oil can cause sticking valves and restrictions in valve orifices.
The pressure setting of the bypass valve in parking brake release oil filter (6) is
Problem: Rubber particles are found.
Probable Cause
- Seal failure
- Hose failure
Problem: Shiny steel particles are found.
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| Illustration 4 | g00313886 |
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784C Torque converter, parking brake release, and pulled unit brake cooling gear pump (7) Cover for the torque converter scavenge screen (8) Torque converter scavenge pump section (9) Torque converter charging pump section (10) Parking brake release pump section (11) Pulled unit brake cooling pump | |
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| Illustration 5 | g00313887 |
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785C torque converter and parking brake release gear pump (7) Cover for the torque converter scavenge screen (8) Torque converter scavenge pump section (9) Torque converter charging pump section (10) Parking brake release pump section | |
Probable Cause
- Mechanical failure of parking brake release pump section (10).
Check: Check the torque converter hydraulic filter.
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| Illustration 6 | g00666129 |
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(12) Torque converter hydraulic filter
(23) Bypass switch | |
Remove torque converter hydraulic filter (12). Inspect torque converter hydraulic filter (12) for foreign material. Cut the filter open, if necessary.
Note: Torque converter hydraulic filter (12) has an oil bypass valve. The bypass valve allows the oil to bypass the oil filter element or the screen whenever the pressure difference between the inlet oil and the outlet oil becomes too high. Any oil that does not flow through the filter element or through the screen goes directly into the hydraulic circuit. Dirty oil can cause sticking valves and restrictions in valve orifices.
The pressure setting of the bypass valve in torque converter oil filter (12) is
Problem: Rubber particles are found.
Probable Cause
- Seal failure
- Hose failure
Problem: Shiny steel particles are found.
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| Illustration 7 | g00313886 |
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784C Torque converter, parking brake release, and pulled unit brake cooling gear pump (7) Cover for the torque converter scavenge screen (8) Torque converter scavenge pump section (9) Torque converter charging pump section (10) Parking brake release pump section (11) Pulled unit brake cooling pump | |
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| Illustration 8 | g00313887 |
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785C Torque converter and parking brake release gear pump (7) Cover for the torque converter scavenge screen (8) Torque converter scavenge pump section (9) Torque converter charging pump section (10) Parking brake release pump section | |
Probable Cause
- Mechanical failure of the torque converter charging pump section (9)
Check: Check the torque converter scavenge screen.
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| Illustration 9 | g00313886 |
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784C Torque converter, parking brake release, and pulled unit brake cooling gear pump (7) Cover for the torque converter scavenge screen (8) Torque converter scavenge pump section (9) Torque converter charging pump section (10) Parking brake release pump section (11) Pulled unit brake cooling pump | |
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| Illustration 10 | g00313887 |
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785C Torque converter and parking brake release gear pump (7) Cover for the torque converter scavenge screen (8) Torque converter scavenge pump section (9) Torque converter charging pump section (10) Parking brake release pump section | |
Make sure that the oil has been drained from the hydraulic oil tank and from the torque converter for the next check.
| 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. |
Remove torque converter scavenge screen (7). Inspect torque converter scavenge screen (7) for foreign material or restrictions.
Problem: Rubber particles are found.
Probable Cause
- Seal failure
- Hose failure
Problem: Shiny steel particles are found.
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| Illustration 11 | g00313886 |
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784C Torque converter, parking brake release, and pulled unit brake cooling gear pump (7) Cover for the torque converter scavenge screen (8) Torque converter scavenge pump section (9) Torque converter charging pump section (10) Parking brake release pump section (11) Pulled unit brake cooling pump | |
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| Illustration 12 | g00313887 |
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785C Torque converter and the parking brake release gear pump (7) Cover for the torque converter scavenge screen (8) Torque converter scavenge pump section (9) Torque converter charging pump section (10) Parking brake release pump section | |
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| Illustration 13 | g00313889 |
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(13) Pump drive
(14) Hoist and rear brake cooling gear pump | |
Probable Cause
- Mechanical failure of pump drive (13)
- Mechanical failure of the parking brake release oil pump section (10). See "Check: Check the parking brake release hydraulic filter.".
- Mechanical failure of the torque converter charging pump section (9). See "Check: Check the torque converter hydraulic filter.".
Problem: Aluminum particles are found.
Probable Cause
- Mechanical failure of the torque converter
Problem: Black fiber is found.
Probable Cause
- Worn lockup clutch in the torque converter
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| Illustration 14 | g00352772 |
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(2) Rear brake oil coolers
(3) Screens for the rear brake oil coolers | |
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| Illustration 15 | g00482640 |
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(16) Torque converter and front brake cooling screen
(23) Bypass switch | |
Remove screens (3) and (16) for the front and rear brake oil coolers. Inspect screens (3) and (16).
Problem: Rubber particles are found.
Probable Cause
- Seal failure
- Hose failure
Problem: Shiny steel particles are found in the torque converter and front brake cooling screen.
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| Illustration 16 | g00313886 |
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784C Torque converter, parking brake release, and pulled unit brake cooling gear pump (7) Cover for the torque converter scavenge screen (8) Torque converter scavenge pump section (9) Torque converter charging pump section (10) Parking brake release pump section (11) Pulled unit brake cooling pump | |
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| Illustration 17 | g00313887 |
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785C Torque converter and the parking brake release gear pump (7) Cover for the torque converter scavenge screen (8) Torque converter scavenge pump section (9) Torque converter charging pump section (10) Parking brake release pump section | |
Probable Cause
- Mechanical failure of torque converter charging pump section (9). See "Check: Check the torque converter hydraulic filter.".
Probable Cause
- Mechanical failure of the torque converter
Problem: Black fiber is found in the torque converter and front brake cooling screen.
Probable Cause
- Worn lockup clutch in the torque converter
Problem: Shiny steel particles are found in the screen for the rear brakes.
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| Illustration 18 | g00313889 |
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(13) Pump drive
(14) Hoist and rear brake cooling gear pump | |
Probable Cause
- Mechanical failure of the hoist and rear brake cooling gear pump (14)
Problem: Aluminum particles are found in the rear brake cooling screens.
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| Illustration 19 | g00313889 |
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(13) Pump drive
(14) Hoist and rear brake cooling gear pump | |
Note: A small amount of aluminum particles is normal.
Probable Cause
- Mechanical failure of the hoist and rear brake cooling gear pump (14) See "Check: Check the hoist and rear brake cooling screens.".
Check: Check the hoist and rear brake cooling screens.
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| Illustration 20 | g00482247 |
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(17) Oil screen for hoist
(18) Oil screen for the rear brake cooling (23) Bypass switch | |
Remove oil screens (17) and (18). Inspect screens (17) and (18) for foreign material or for restrictions.
Problem: Rubber particles are found.
Probable Cause
- Seal failure
- Hose failure
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| Illustration 21 | g00313889 |
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(13) Pump drive
(14) Hoist and rear brake cooling gear pump | |
Note: A small amount of aluminum particles is normal.
Probable Cause
- Mechanical failure of the hoist and rear brake cooling gear pump (14)
Check: Check the inside of the hydraulic tank.
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| Illustration 22 | g00482256 |
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(20) Suction screen for torque converter and parking brake release oil
(21) Suction screens for hoist and rear brake cooling oil | |
Drain the oil from the hydraulic tank. Remove the outer cover from the hydraulic tank. Inspect the bottom of the hydraulic tank for debris. Remove the hoses from the back of the hydraulic tank in order to remove suction screens (20) and (22) and clean the suction screens.
| 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. |
Problem: Rubber particles are found.
Probable Cause
- Seal failure
- Hose failure
Problem: Shiny steel particles are found.
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| Illustration 23 | g00313886 |
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784C Torque converter, parking brake release, and pulled unit brake cooling gear pump (7) Cover for the torque converter scavenge screen (8) Torque converter scavenge pump section (9) Torque converter charging pump section (10) Parking brake release pump section (11) Pulled unit brake cooling pump | |
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| Illustration 24 | g00313887 |
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785C Torque converter and parking brake release gear pump (7) Cover for the torque converter scavenge screen (8) Torque converter scavenge pump section (9) Torque converter charging pump section (10) Parking brake release pump section | |
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| Illustration 25 | g00313889 |
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(13) Pump drive
(14) Hoist and rear brake cooling gear pump | |
Probable Cause
- Mechanical failure of the torque converter scavenge pump section (8)
- Mechanical failure of parking brake release pump section (10). See "Check: Check the parking brake release hydraulic filter.".
- Mechanical failure of the torque converter charging pump section (9). See "Check: Check the torque converter hydraulic filter.".
- Mechanical failure of oil pump drive (13). See "Check: Check the torque converter scavenge screen.".
- Mechanical failure of rear brake cooling pump section (11). See "Check: Check the torque converter and front brake cooling screen. Check the oil cooler screens for the rear brakes.". Inspect screens (3).
Problem: Aluminum particles are found.
Probable Cause
- Mechanical failure of the torque converter See "Check: Check the torque converter scavenge screen.".
Problem: A large quantity of aluminum particles are found.
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| Illustration 26 | g00313889 |
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(13) Pump drive
(14) Hoist and rear brake cooling gear pump | |
Note: A small amount of aluminum particles is normal.
Probable Cause
- Mechanical failure of the hoist and rear brake cooling gear pump (14)
Problem: Black fiber is found.
Probable Cause
- Failure of the wheel brakes
- There is a worn lockup clutch in the torque converter. See "Check: Check the torque converter scavenge screen." and "Check: Check the torque converter and front brake cooling screen. Check the oil cooler screens for the rear brakes.".
Problem: Shiny steel particles and/or chrome particles are found.
Probable Cause
- There is a mechanical failure of a hydraulic cylinder and/or of a cylinder rod. Inspect the cylinder rods for scoring.
Note: If any of the above particles are found during any visual checks, all components of the hoist, of the torque converter, and of the brake cooling system must be cleaned. Do not use any damaged parts. Damaged parts must be replaced with new parts.