Gear Oil

[Joe C.]

I filled the diff and Muncie of my '65 with 85W-140 gear oil. I would like to do the same with the diff of my '85. I figure, that neither is driven in cold temps, and I like the idea of more viscosity at higher temps. Is it a good idea? If you recommend the standard 80W-90, then why so. I do realize that the highway fuel economy will decrease by .002 MPG.
Thanks in advance.
Joe

[John H.]

Re: Gear Oil

Joe -

I go with what the GM recommendation is for lubricants - that's what they were designed, developed, and durability-tested with. Race cars are a different animal.

[Joe L.]

Re: Gear Oil

Joe and John-----

Absolutely, positively agree with John. I would not even consider using anything other than a GL-5 rated 80W-90 gear lube for the differential of any C4 Corvette. That's what GM recommends, that's what Dana (the manufacturer of the C4 differentials) recommends and that's all that I'd use. Period.

Also, I wouldn't use anything but 75W-90 or 80W-90 for a Muncie transmission, either.