A front axle seal is a metal and rubber device used to not only prevent axle lube from seeping out of the axle housing, but it is also designed to prevent dirt, water and contamination from gaining access into the axle housing and contaminating the gear lube. Found in the front axle of a four-wheel drive vehicle, the front axle seal is located inside of the differential housing in most cases. In certain applications, the front axle may contain a seal further out in the front axle, towards the steering knuckle. This type of installation is common in non-locking front hub designs that require lubrication of a vacuum modulator, located in the axle, to lock the outer axles with a splined-center link to engage the locking of the front axle.
Requiring no service or preventative maintenance, the first indication of a failed or failing front axle seal is typically an oil spot underneath the axle on the driveway or parking lot. At first glance, the seepage may appear minor and insignificant, however, any front axle seal that allows the very thick and heavy gear lubricant to leak out of the axle housing will also permit water to find its way into the housing. Even the smallest amount of water finding its way past the seal has the potential to damage the gear lube and the gear set.
Replacement of the front axle seal is a very involved procedure, commonly requiring the front wheels to be removed from the vehicle to allow access into the front axle housing. The seals are located on the inside of the differential or the pumpkin, the large round center section of the axle, so the axle lube requires draining from the differential before the differential cover can be removed. With the differential cover removed, the steering knuckles must be removed and the axles pulled out of the axle housing. Once this has been accomplished, the old front seals can be removed and the new seals installed in the axle tubes.
It is imperative that the new seals be positioned properly with the seal bevel, or lip, pointed in the right direction, according to manufacturer's directions. Failure to follow this direction will result in a leaking front axle seal. The lip of the seal must also be lubricated with a thin layer of gear lube wiped on the seal applied with a clean finger or cloth. This will prevent the front axle seal from being damaged by friction as the axle is slid into the differential.