The rear axels in C4
Corvettes are from Dana Corporation http://www.dana.com/
does not specify a service interval in the owners manual. Dana Corporation
makes the following recommendations:
1. If there is any
possibility of water contamination the oil needs to be changed
2. If the axle temperature spend a lot of time at
or above 275F, the oil should be changed every 30,000 miles and the set up
and bearings should be checked every time. This should only be a factor
when you are getting a good amount of track time.
normal use, the oil should be changed at 75,000 miles.
you are getting chatter (noise) from the rear end, you may want try
changing the oil or at least adding some limited slip additive.
Dana Corp says that the factory oil is adequate, but
synthetics are superior especially when heat is an issue. A limited slip
additive should always be used. Gear oil should have a GL-5 rating and a
75w-140 or 75w-90 weight, with 75w-140 being the preferred weight.