Rear Axle Oil

[Ron Schaller]

I have a 1989 C4 with only 14,500 miles. I bought it last August. I am in the process of changing all filters, fluids, etc. so that I will have a base reference for all maintenance items. I looked at draining the rear axle, but it is obviously a very complicated task. As an alternative, would it be worthwhile for me to pump out all the oil that I can and then replace it with fresh oil along with the positraction oil supplement from GM? Or should I just leave the rear axle as it is?

Any advice will be appreciated.

Thanks
Ron S.

[Joe L.]

Re: Rear Axle Oil

Ron-----

GM specifies no change interval on the rear axle gear lube. At the kind of mileage that this car has, unless you have reason to believe that the car has been brutally abused, I'd leave it just the way it is. Simply check it to be sure that the level is right and there are no leaks.

[Duke W.]

Re: Rear Axle Oil

I recommend you change the oil. Siphoning or pumping the oil out of the
filler plug is not a difficult task. Use the GM axle oil or a quality 80W-90
GL-5 non-synthetic axle oil along with one bottle of GM positraction additive.
Buy a second in case the clutches chatter. If they do add half a bottle (2 oz.)

As the positraction cluthes wear the particles form a sludge at the bottom of the housing. Granted, your car doesn't have many miles, but age takes a
toll, too.

I would recommend you renew all the fluids. GM doesn't recommend brake fluid changes either, which is one reason why many cars need hydraulic component overhauls. Had GM recommended the typical one to two year brake fluid changes recommended by the European OEs a lot less money would have been spent over
the years overhauling calipers and cylinders, assuming owners had been
diligent enough to actually change the fluid when recommended.

Duke

[Dick W.]

Re: Rear Axle Oil

Another good reason to change the differential oil is moisture. The housing is a rather large cavity with a small amount of fluid. Over time the heating and cooling of a vehicle in storage, with the limited driving to heat the oil to boil off the moisture, will accumulate a small quantity of water. I do not need to spell out what moisture does.

I would drive the car briefly, to get any contaminats in suspension, before I siphoned the fluid.

[Mike Cobine]

Re: Rear Axle Oil

Had GM recommended the typical one to two year brake fluid changes recommended by the European OEs a lot less money would have been spent over
the years

Duke,
If GM had recommended all the things it could to extend the life of a car, they wouldn't have been selling a new one to customers every year or two years like they wanted. We tend to forget, GM is in the business of selling cars EVERY YEAR, not selling cars that last for two or three generations.

The only reason to imply that a car will last a long time is to imply some sort of value so the customer will buy it. Then hopefully, they will tire of it and buy a new one in two years.