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Southern California 1994-1996 Impala SS Owners

IMPALA SS DIFFERENTIAL EXPOSED

There is a controversy about the need for holes in the rear axle housing cover gasket corresponding to the oil passages in the rear axle housing. Many police agencies are reporting wheel bearing failures at about 70,000 miles because of insufficient lubrication. A popular modification therefore is to replace the standard G.M. cover gasket, which has no holes to allow oil to pass, with a Fel-Pro gasket, which does. There have been many statements made about whether or not this change is needed. One theory is that there aren't any oil passages in the rear axle housing and therefore holes in the gasket aren't needed. The following picture pretty much disproves that theory.

A tool has been inserted through the oil passage hole on the right side of the rear axle housing. There is also a similar hole on the left side of the axel housing. The tip of the tool is where the differential side bearing goes. This shows that the oil passage holes are outboard of the differential side bearings.

Oil in the rear axle housing is agitated by the gears. A little of the oil that is flying around inside the axle housing is picked up by scrapers in the rear axle housing cover and directed toward the oil passages. The oil goes down the oil passages into the axle tubes and, from there, flows to the wheel bearings -- lubricating them. When the car is stopped, a little oil seeps through the differential side bearings into the axle tube because the oil level is higher than the lowest part of the bearings.

The parts that have been removed in the picture are the differential ring gear, the Auburn differential case, and both axle shafts. The pinion gear is what's laying in the bottom of the rear axle housing.

The next picture shows the rear axle housing cover. You can see two slots in the cover in the same position as the oil passage holes in the rear axle housing. What isn't clear in the picture is that there are little metal "scoops" under the lip of the cover to direct oil through the slot in the cover and into the oil passage holes in the rear axle housing.

Apparently General Motors is now telling its mechanics that G.M. changed to the no-hole gasket because too much differential fluid was going through the oil passages and down the axle tubes. This was robbing the differential of lubrication. General Motors claims that normal stop and go traffic with turns will allow enough lubrication to get to the axle bearings. Only cars that do a lot of highway driving need to change their cover gaskets to ones with oil passage holes. As proof, G.M. points out that the only axle bearing problems reported are on police cars. Not a single taxi has reported the problem.

So what should you do? General Motors has changed their story more times than O.J. has. Whatever G.M.'s story is, it is clear that police agencies are replacing rear axle housings if they use the standard cover gaskets.

If you use a Fel-Pro gasket (p/n RDS 55028-1) with the correct lubrication holes, you won't have a bearing problem. Just remember to check the fluid in the rear axle housing more often than the manual recommends.

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Last Update: 1/2/99