The oil has not been changed at proper intervals.

1. Drain the oil.
2. Replace the oil filter. Refer to Transmission Fluid Pan and Filter Replacement .
3. Replace the external oil filter. Refer to External Transmission Oil Filter Replacement .
4. Fill the transmission with new oil. Refer to Transmission Fluid Check .

The heat of the oil is excessive.

Check the transmission oil cooler. Refer to Transmission Oil Cooler Description . in Engine Cooling.

The clutch is inoperative.

Overhaul the transmission. Refer to Allison service manuals.

The filter or filter elements are damaged.

Replace the filter or elements. Refer to External Transmission Oil Filter Replacement .

The engine rear oil seal is faulty.

Replace the engine rear oil seal. Refer to 7.2L Diesel Engine.