Doing a frame off on a 1969 convertible and have finished cleaning and refinishing the differential casing. I am having a hard time finding a straight 90W oil. I can find plenty of 80-90W but not single weight 90W. Any thought on using the 80-90W with the GM Limited Slip additive? Thanks for comments/suggestion. Steve
Differential Gear Oil
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Re: Differential Gear Oil
Doing a frame off on a 1969 convertible and have finished cleaning and refinishing the differential casing. I am having a hard time finding a straight 90W oil. I can find plenty of 80-90W but not single weight 90W. Any thought on using the 80-90W with the GM Limited Slip additive? Thanks for comments/suggestion. Steve
Steve-----
GM never specified 90 wt lubricant. What was specified was 80 wt OR 80-90 wt. Use GM #88863089 in conjunction with the posi additive.In Appreciation of John Hinckley- Top
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Re: Differential Gear Oil
Steve
Any quality 80-90 wt will work, I use non synthetic Lucas 85-140 in my builds with the GM additive. The GM product Joe mentions will work fine. Many guys like to use a certain brand and type, some swear by synthetic but I haven't had any issue with the Lucas or GM oils.- Top
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Re: Differential Gear Oil
At the risk of sounding heretical, the local mechanic that recently rebuilt the diff for my '80 swears by the Ford additive. Says it sticks and lubes better. Given the sheer number of Corvettes they own and work on, I didn't have a reason offhand to question him.
I had a bottle of the GM additive, but elected to test his theory. Once the car gets rolling, we'll see...-Kenn
1970 LS-5
1970 350/300
1980 L-48
2004 LS-1- Top
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Re: Differential Gear Oil
At the risk of sounding heretical, the local mechanic that recently rebuilt the diff for my '80 swears by the Ford additive. Says it sticks and lubes better. Given the sheer number of Corvettes they own and work on, I didn't have a reason offhand to question him.
I had a bottle of the GM additive, but elected to test his theory. Once the car gets rolling, we'll see...
Kenn------
They may be exactly the same thing. GM does not now nor ever has manufactured this additive. I highly doubt that Ford does, either.In Appreciation of John Hinckley- Top
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Re: Differential Gear Oil
The original spec oil was Mil-L-2105D, but that Mil-Spec was cancelled some years ago and replaced by the commercial spec SAE 80W-90 GL-5. commonly called "90-weight". Any brand is okay as long as the bottle has the API "donut" with that information.
I don't think there is any difference between the limited slip differential additive sold by GM, Ford Chrysler, Mercedes, or any other manufacture that offers clutch type limited slip differentials.
You can also buy it from NAPA for probably a lot less than any dealer parts department.
Duke- Top
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