Testing and Adjusting 784C and 785C Off-Highway Truck/Tractors Power Train. The rear axle is a common sump for the differential and both final drives

Testing and Adjusting 784C and 785C Off-Highway Truck/Tractors Power Train

Visual Inspection (Rear Axle and Final Drive)

SMCS - 4004; 4011; 4050

Use the visual checks to troubleshoot a problem. Perform the checks with a stopped engine and with engaged parking brakes. During the checks, use a magnet to separate the ferrous particles from the nonferrous particles.

Note: The rear axle is a common sump for the differential and both final drives.

Check: Check the oil level in the final drive, and check the filler plug.

Remove filler plug (2). The filler plug (2) is magnetic. Check the filler plug (2) for metallic particles. Check the oil level in each final drive. When the oil level is checked, be certain that drain plug (1) is down in the lowest position. Check for oil leakage on the rear tires and wheels. Refer to your Operation and Maintenance Manual in order to determine the correct oil to use.

Problem: The filler plug has metal shavings.

Probable Cause

• Mechanical failure of one or both of the final drives
• Mechanical failure of any of the components that are located inside the rear axle housing

Problem: The oil level in a final drive is too high and the oil level in the hydraulic tank is too low.

Probable Cause

• The brake cooling oil is leaking into the final drive. Duo-Cone seal (5) at the rear wheel brake has failed.
• The brake cooling oil is leaking into the final drive. Seal assembly (3) at the rear wheel brake has failed.
• The brake cooling oil is leaking into the final drive. O-ring seal (6) at the rear wheel brake has failed.

Note: To determine the wheel that is leaking, perform the test in the Air System and Brakes Systems Operation/Testing and Adjusting, "Internal Brake Leakage - Check".

Problem: The oil level in a final drive is too low.

Probable Cause

• The probable cause is the failure of the O-ring seal on the final drive housing.

Check: Check the oil level in the rear axle housing.

Use the sight glass (7) in order to check the oil level in the rear axle housing. The oil level should be at the bottom of the sight gauge. Check for leakage under the housing. Refer to your Operation and Maintenance Manual in order to determine the correct oil to use.

Problem: The oil level in the rear axle housing is too high and the oil level in the hydraulic tank is too low.

Probable Cause

• The brake cooling oil is leaking into the final drive. Duo-Cone seal (5) at the rear wheel brake has failed.
• The brake cooling oil is leaking into the final drive. seal assembly (3) at the rear wheel brake has failed.
• The brake cooling oil is leaking into the final drive. O-ring seal (6) at the rear wheel brake has failed.

Note: To determine the wheel that is leaking, perform the test in the Air System and Brakes Systems Operation/Testing and Adjusting, "Internal Brake Leakage - Check".

Problem: The oil level in the rear axle housing is too low and the oil level in the transmission section of the hydraulic tank is too high.

Probable Cause

The oil of the differential and bevel gear is leaking into the transmission case. This could be caused by one of the following problems:

• Failure of the pinion seal in the differential
• The center plug of the differential pinion is not installed or the center plug is leaking.

Check: Check the rear axle power train filter.

Remove rear axle power train filter (8). Inspect the filter for foreign material. The filter might need to be cut apart for inspection.

Note: Rear axle power train filter (8) has an oil filter bypass valve. An oil filter bypass valve allows oil to bypass the oil filter when the pressure difference between the inlet oil and the outlet oil at the oil filter is too high.

The difference of the pressure setting of the bypass valve in rear axle power train filter (8) is approximately 250 kPa (36 psi).

Problem: Rubber particles are found.

Probable Cause

• The probable cause is either seal failure or hose failure.

Problem: Shiny steel particles are found.

Probable Cause

• Mechanical failure of any of the components that are located inside