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my friend wants to change his ring and pinion to a 3.90 or 3.91 gear. we want to do it on our own to save money. ive seen this forum and it was very helpfull 3.91 Gear Install...GHETTO Style - LS1GTO.com Forums. i have only worked on rearends from early corvettes (60-70's) i believe it is close to the same.

but the one thing i am concerned with is the shimming of the pinion i hear we may need a .002 shim but i am unsure.

also what gear will fit in the carrier where can i buy it from we found this on summit and im curious if it is what we need Motive Gear GM10-390 - Motive Gear Ring and Pinion Sets - Overview - SummitRacing.com

Any advise is appreciated.

Thanks
Anthony
 

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Those are not the gears for these cars. GTOs have their own rear diff all together, only a couple different manufacturers make them. There are 3.91's out there, though. I would suggest getting an install kit with your gears, that will have extra shim in it in case you need them. I have set up several gear sets so far, and every time the factory shim is the one I ended up using, so start with that.
 
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