There is dirt in the transmission oil.

Replace the transmission oil.

The lubricant is incorrect.

Replace the transmission oil.

The oil level is low.

Fill the transmission to the proper oil level.

The bearing retainer is worn or broken.

Overhaul the transmission.

Water or contaminants are in the transmission oil.

Replace the transmission oil.

The engine torque is too high for the transmission.

Adjust the engine torque.

The vehicle is overloaded.

Load the vehicle to the proper load limit.

There is excessive transmission vibration.

Overhaul the transmission.