Differential fluid

[Douglas B.]

Does anyone have a preference on differential fluids? I have a 78 L48 coupe.

[John H.]

Re: Differential fluid

Mine have always worked fine with what GM recommended - GM Diff Lube (or ordinary 75W90 or 80W90 hypoid lube) and GM Posi Additive. No need for any "miracle" lubes or additives.

[Clem Z.]

i have used amsoil gear lube for years

with great results. back racing corvettes amsoil was the only gear oil that would let the posi last. also add the GM posi additive to the amsoil

[Duke W.]

Re: Differential fluid

Anything labeled 80W-90 GL-5 plus one four-oz. bottle of the GM additive if you have Positraction.

Duke

[Clem Z.]

is that synthetic gear lube because with

regular gear oil GM says change the lube every 7500 miles. my silverado started to have the posi chattering in the turns after about 6000/7000 miles so i switched to amsoil and GM additive about 125,000 miles ago and have never changed it since even after pulling race car trailers. the posi still works great with no problems.

[Joe C.]

Re: is that synthetic gear lube because with

Clem;

From what I've seen, the synthetic gear lubes are 85W-90, and most already contain conditioners for the clutches. Standard mineral based lubes are 80W-90, do not contain the conditioners, and seem to be getting harder to find.

Joe

[Gary S.]

Re: is that synthetic gear lube because with

There has been enough anecdotal evidence from posts here to indicate that, although some manufacturers claim that their product is all-inclusive, the differentials seem to run better with GM Posi additive.

Fwiw, I use Mobil 1 gear lube and the GM posi additive.

Gary

[Joe C.]

Re: is that synthetic gear lube because with

Gary,

That is precisely the reason that I don't use synthetic gear oil.........I can't be certain of the additive package. I use mineral based lube with the minimum amount of friction modifyer (not necessarily GM) to prevent clutch chatter........usually 4 ounces.
I usually use 80W-90, but this time I used a 50/50 mix of 80W-90 and 90W-140, for both Corvette's diffs. I never drive either one of them in winter, so the extra viscosity is, IMHO, better protection in the hot weather.

Joe

PS: I don't use synthetic motor oil, either. It's too expensive, and I change the oil frequently, which is most imortant to prevent sulfuric acid buildup.