TM 10-3930-653-14&P TROUBLESHOOTING GUIDE Trouble Probable Cause Remedy 1.  Noisy differential. Attention should be paid to noise from the differential since abnormal noise could mean it is out of order.  However, It is easy to mistake the sound from the engine, transmission, muffler, reduction gear, drive wheels, or wheel bearings for that of the differential.  Before attempting any repairs on the differential, make certain that the abnormal noise comes from the differential. (1) Noisy gears during accelerating.   Lack of lubricating oil or improper Refill or replace oil. quality of oil. (SAE 90) Ring gear teeth worn or damaged. Repair or replace. Bearings worn or broken. Replace. Drive shaft spline worn. Replace. (2) Noisy gears during traveling.   Pinion gear teeth or side gear teeth Repair or replace. worn or damaged. Worn thrust plate of pinion gear or   Replace. side gear. Pinion shaft worn. Replace. (3) Noise is heard when steering.   Pinion gear, side gear, or pinion shaft Replace worn out worn. part. 2.  Truck does not drive. When the truck does not drive properly, check the differential by turning one wheel with front wheel jacked up.  After making certain the differential is out of order, proceed with the troubleshooting of the differential. (1) Truck can not travel or violent Metal piece(s) is(are) mixed in the   Remove. noise is heard. unit. Broken bearing. Replace. Drive shaft damaged. Replace. Ring gear teeth damaged. Replace gear. 4 - 188