A rear axle seal is a device that retains the gear lubricant inside of the rear axle and prevents the lubricant from seeping out of the axle housing from around the axle shaft. A circular metal device with a soft rubber lip, the rear axle seal is placed inside of the axle housing tube and fits snugly around the axle shaft. Gear lubricant from within the axle housing maintains the lubrication of the rear axle seal, preventing the seal from tearing or burning and a small dab of gear lube or oil, wiped on the lip of the seal during installation, provides initial lubrication.
While a modern rear axle seal design uses steel and rubber to retain the rear axle lube, early versions of the seal were constructed from leather or cotton rope. The early versions of rear axle seal prevented large amounts of lube from escaping the axle housing, however, the rope and leather versions did not completely seal the axle, and most housings dripped a small amount of gear lube onto the streets and parking spots. In some racing applications, it was typical for a team to pack the axle tube with oil-soaked rags in an attempt to create a better rear axle seal.
To change a leaking rear axle seal, it is necessary to remove the wheel and tire from the targeted axle. Once the tire is removed, the axle is removed from the axle housing in a manner that is typical for the type of axle being used on the vehicle. Depending on the axle housing's year, type and manufacturer, there are several different methods of removing the axle from the differential and axle housing. With the axle removed, the rear axle seal can be removed from the bearing cup on the end of the axle housing with a seal removal tool. If a special tool is not available, a screwdriver, claw hammer or pry bar can often be substituted.
Once the old seal is removed, the axle's bearing cup can be cleaned and the new seal can be installed in the axle tube. It is recommended by most seal manufacturers that a small amount of silicone be placed on the outer diameter of the seal prior to placing it inside of the housing. It is also important to ensure the inner lip of the new seal is facing toward the axle center section in order to achieve a proper seal. In some instances, the new rear axle seal will require a light tap around the outside edge with a hammer to properly seat the seal in the axle tube.