What gear oil do I use?
Thread Starter
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
What gear oil do I use?
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!
Team Owner
Joined: Dec 1999
Posts: 34,873
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From: Lacey WA RVN 68-69
NCM Sinkhole Donor
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.
Thread Starter
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
I read online that you should only use GL4 oils for it, not GL5? Am I missing something?
Team Owner
Joined: Dec 1999
Posts: 34,873
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From: Lacey WA RVN 68-69
NCM Sinkhole Donor
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.
Safety Car
Joined: Aug 2013
Posts: 4,429
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From: Minneapolis Mn
Are there any bronze parts in it?
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 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.
Melting Slicks
Joined: May 2013
Posts: 2,692
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From: Sacramento California
80w90 GL5 gear oil will work fine. I would be very surprised if you had any trouble using this fluid in the 4-speed portion of your 4+3 manual.
The OP is looking to fill a manual transmission, not a differential.
The OP is looking to fill a manual transmission, not a differential.
Oil Producer
Joined: Apr 2014
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Racer
Joined: Aug 2008
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From: Justin TX
I run amsoil synthetic in everything, no worries about the additive for limited slip ... Www.amsoil.com and use the vehicle product selector
Team Owner
Joined: Sep 2003
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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 ------
Last edited by WVZR-1; Oct 8, 2015 at 12:20 AM.