Rear differentials have bearings at both wheels. The bearings allow the axle shafts to rotate with little friction. As long as they are properly lubricated, they can last the life of the vehicle. If not they can cost a huge amount to repair.

Axle bearing failure is a very expensive problem. On most modern rear differentials, the axle bearings roll directly on the axle shaft. When the bearing fails, the shaft(s) are almost always damaged. Axle shafts often cost in excess of $500.00 each and this damage is very often preventable.

The above axle damage started out as a very small pinion seal leak. Most rear differentials hold about two to three quarts of lubricant. This heavy oil lubricates the gears and a small amount runs down the axle tubes to lubricate the axle bearings.

The housing is designed so that the fluid level is slightly above the axle tubes. Only a small amount of oil reaches the axle bearings. This is by design to keep the axle seals from being overwhelmed. As long as the differential is full, everything is fine.

Sometimes the pinion seal, at the front of the differential can leak. When this happens oil will be loss. The problem is, once a small amount is loss, the oil level is no longer above the pinion seal. The seal quits leaking, but the axle bearings also quit receiving the oil they need.

Losing as little as two-pints of oil can cause axle damage. All too often, the loss goes unnoticed until it is too late. The rear differential should be inspected for leaks at every oil change. The level should be checked whenever there is a sign of a leak and the fluid should be replaced around 50,000 to 100,000 miles. If the vehicle is used for towing, much more frequent oil replacement may be needed.

Having the differential oil checked and replaced can save you big money. It’s one more reason for a good maintenance program. AGCO, it’s the place to go.