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Old January 17th, 2020, 02:50 AM
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LEWISMATKIN LEWISMATKIN is offline
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Join Date: Jan 2013
Location: RIDGE MANOR, FLORIDA
Truck: 1965 1002 GMC V6-305E
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Default Re: New to the Group

Quote:
Originally Posted by tbucketnut View Post
I use the NAPA 90 weight mineral oil in the sm420 and recommend it for the ones I rebuild for people, I found the newer more slippery 90 weights can make for bad shifts with the 3rd and clutch gear synchros in my opinion. Runs about 15 bucks a gallon takes between 6-6.5 pints.
I dont think you can go wrong with any hypoid gear lube for GL-2 through 5 for the diff. If you have a clutch type limited slip or posi you will need friction modifier.

Steve
The only problem with using mineral oil in any gear box is the fact that mineral oil won't mix with EP rated lubricant-if any EP lube is introduced into the lube, it will cause a chemical reaction causing the mineral oil to coagulate like blood clotting and causing all the bearings, syncronizers, and bushings to fail. If you use it, make sure that is all that goes in whatever you put it in.
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Last edited by LEWISMATKIN; January 17th, 2020 at 02:53 AM. Reason: spelling
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