793C Off-Highway Truck Hydraulic System Caterpillar

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Personal injury or death can result if the proper procedure is not followed. Make reference to the WARNING on the first page of the Testing and Adjusting section.

Perform the visual checks before you troubleshoot a problem. Make sure that the transmission is in neutral and stop the engine. During the visual checks, use a magnet to separate ferrous particles (iron and steel) from nonferrous particles (aluminum, rubber and bronze).

1. Check the oil level in the hydraulic tank.

2. Check for oil leakage.

3. Check the parking brake release oil filter.

4. Check the front brake oil filters and the screens of the rear brake oil cooler.

5. Check the hoist screens.

6. Check the parts inside the hydraulic tank.

Check 1:

Illustration 1	g00288130
(1) Rear brake oil coolers are behind the right front tire.

Illustration 2	g00288131
(2) Front brake oil cooler is under the upper cross frame member.

Check the oil level in the hydraulic tank. Look for air or water in the sight gauge. Add oil to the hydraulic tank, if necessary. See the Operation and Maintenance Manual for the correct type of oil.

Problem 1:

There is an indication of water in the oil.

Probable Cause:

• Failure of either of rear brake oil coolers (1)

• Failure of front brake oil cooler (2)

Problem 2:

There is an indication of air in the oil.

Probable Cause:

• There is a leakage in the oil lines. Perform Visual Check 2.

Problem 3:

The oil level is too low.

Probable Cause:

• There is a leakage in the oil lines. Perform Visual Check 2. Add oil before you perform any tests.

Illustration 3	g00288132
Final Drive Plug

Note: Check the oil in each final drive. Brake cooling oil may leak into the final drive.

Check 2:

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 3:

Illustration 4	g00288133
(3) Parking brake release oil filter is behind the right front tire.

Remove parking brake release oil filter (3). Inspect parking brake release oil filter (3) for foreign material. Cut the filter open, if necessary.

Note: Parking brake release oil filter (3) 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 (3) is 248 kPa (36 psi).

Problem 1:

Rubber particles are found.

Probable Cause:

• Seal failure

• Hose failure

Illustration 5	g00288134
(5) Parking brake release pump section is on the oil pump drive.

Problem 2:

Shiny steel particles are found.

Probable Cause:

• Mechanical failure of parking brake release pump section (5)

Check 4:

Illustration 6	g00288135
Rear Brake Oil Coolers (6) Screen.

Illustration 7	g00288216
Front Brake Oil Cooler (7) Oil filters are in front of the fuel tank.

Remove screens (6) for the rear brake oil coolers. Inspect screens (6). Cut the screens open, if necessary. Remove oil filters (7) for the front brake oil coolers. Inspect oil filters (7) .

Problem 1:

Rubber particles are found.

Probable Cause:

• Seal failure

• Hose failure

Illustration 8	g00288217
(8) Brake cooling pump section.

Problem 2:

Shiny steel particles are found in screen (6) .

Probable Cause:

• Mechanical failure of any brake cooling pump section (8)

Illustration 9	g00288134
Oil Pump Drive (5) Parking brake release pump section.

Illustration 10	g00288218
Oil Pump Drive (9) Two-section pump (hoist and front brake cooling).

Problem 3:

Shiny steel particles are found in oil filters (7) for the front brake oil coolers.

Probable Cause:

• There is a mechanical failure of parking brake release pump section (5). See Check 3.

• There is a mechanical failure of two-section pump (9). See Check 5.

Check 5:

Illustration 11	g00288219
Hoist Control Valve (10) Hoist screens.

Remove hoist screens (10). Inspect hoist screens (10) for foreign material or for restrictions.

Problem 1:

Rubber particles are found.

Probable Cause:

• Seal failure

• Hose failure

Illustration 12	g00288218
Oil Pump Drive (9) Two-section pump (hoist and front brake cooling).

Problem 2:

Shiny steel particles are found.

Probable Cause:

• Mechanical failure of two-section pump (9)

Check 6:

Illustration 13	g00288220
Rear of Hydraulic Tank (11) Tank drain. (12) Suction screens (hoist). (13) Suction screen (brake cooling and parking brake release). (14) Suction screens (brake cooling).

Drain the oil from the hydraulic tank at tank drain (11). Inspect the bottom of the hydraulic tank for debris. Remove suction screens (12), (13), and (14) and clean the suction screens. Remove the screens which surround each rear brake oil cooler relief valve. Inspect these screens for foreign materials.

Problem 1:

Rubber particles are found.

Probable Cause:

• Seal failure

• Hose failure

Illustration 14	g00288221
(5) Parking brake release pump section. (8) Brake cooling pump section. (9) Two-section pump (hoist and front brake cooling) is on the oil pump drive.

Problem 2:

Shiny steel particles are found.

Probable Cause:

• There is a mechanical failure of parking brake release pump section (5). Perform Check 3.

• There is a mechanical failure of brake cooling pump section (9). Perform Check 4.

• There is a mechanical failure of two-section pump (9). Perform Check 5.

Problem 3:

Pieces of red, nonferrous material are found. These pieces are part of the brake disc.

Probable Cause:

• Failure of the wheel brakes

Problem 4:

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 hydraulic system and of the brake cooling system must be cleaned. Do not use any damaged parts. Damaged parts must be replaced with new parts.