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I've looked at a few parts store and I am trying to find a 75w-90 gear oil that is GL4 and not synthetic for my manual trans part of the 4+3 on a 1985 Corvette. Can't find it anywhere. Does anyone know a specific brand that has what I'm looking for that can be purchased locally? Thanks!
You can use a 80W-90 GL5 gear oil. Any parts store should carry it. That oil weight is very common for a Borg-Warner Super T-10. That's the spec in my '87 owner's manual for the 4-speed part of the 4+3.
You can use a 80W-90 GL5 gear oil. Any parts store should carry it. That oil weight is very common for a Borg-Warner Super T-10. That's the spec in my '87 owner's manual for the 4-speed part of the 4+3.
I read online that you should only use GL4 oils for it, not GL5? Am I missing something?
I read online that you should only use GL4 oils for it, not GL5? Am I missing something?
The 80W-90 GL5 specification is what is in the owner's manual. It's also in the FSM. I'll put more faith in that over "online" information. Do you recall where online you saw that? GL4 is an older spec and GL5 superseded it. Now, I have read that Muncie 4-speed transmissions do use a GL4 gear oil and most people say not to use a synthetic gear oil in a Muncie box. But remember that the older Muncie 4-speed and the newer B-W Super T-10 are not necessarily equal in terms of engineering.
There are some European and even some Asian cars with manual trans that call for GL4. GL5 will handle higher horsepower and "shock loads" much better than a GL4 oil.
I ran into something the other year while working on a wood planer that called for 80w-90 GL3 lube for the gearbox. I could only find GL4 in that weight. During my research I found reference that true GL4 lube would attack bronze parts. I spent some time talking with Valvoline about their lube. They told me they de-something-or-other (can't remember the exact name) their lube so though it's a GL4 lube it won't attack any bronze pieces. I've used it now for about 5+ years in my planer and there's no indication of any bronze gear issues.
Not saying it does or doesn't apply here but be aware it might in some situations.
I read online that you should only use GL4 oils for it, not GL5? Am I missing something?
In the Muncie and early Warner '57 - '63 in GM the GL4 was the spec I believe, in the later '74+ Warner and the 4+ the spec I believe was changed to GL5 for all Warner and the 4+, the composition of the rings was changed and GL5 created no issues. When you use the late rings in the early transmissions GL5 I believe becomes the lube of choice.
I haven't checked a '74+ lubricant guide but it might be interesting to.
It gets debated frequently and there's certainly some Internet lore involved. Try reading the C3 section from time to time, there's those that insist ATF/Dexron correct and the "lube of choice" FOR EVERYTHING ------
10-06-2015, 04:09 PM
What gear oil do I use?
