If the defect is in the differential of a 4 by 4, 6 by 6, or 8 by 8 vehicle, remove the propeller shaft and drive axles. For example, if the front rear differential is defective and the rear propeller shaft is removed, the vehicle can still be powered by the front wheels. When the axle shafts are removed, cover the openings securely to keep out dirt and foreign matter.
CAUTION: Avoid unnecessary oil spills by applying materiel over the holes. This also helps retain as much lubricating fluid as possible.
Source: U.S. Army FM 4-30.31, Recovery and Battle Damage Assessment and Repair