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Discussion Starter · #1 ·
We are in the middle of swapping out the ring and pinion on my 2005 GTO. I purchased a set of 3.91 from Difftechnics. We are having a very hard time locating the following information:

Pinion Depth Specification: ???
Side Gear Pre-Load Specification: ???
Torque specs for all bolts: ???

Has anyone installed these gears before, or can anyone point me in the right direction to get this information. I just emailed Difftechnics, so possibly they will have some of the info, but it may be a bit before I hear back from them (Australia time).

Any help would be greatly appreciated. Thank you!
 

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Discussion Starter · #4 ·
3.91 gear install info from Diff Technics

Thank you Kurt from Diff Technics for the following:

IF the 3.46 ratio pinion that you “take” out of the diff has lets say a marking of 0 and then the 3.91’s we sent you have a 2 marked on them this would mean that the 3.91 pinion is .002” further into mesh with the ring gear than the 3.46 so you must remove .002” from the pinion location shim if it was the other way round and the 3.91 pinion had a -2 (negative two) on it this would mean that the pinion is .002” out of mesh with the ring gear centerline, So hence you must ADD .002” to the shim size and if you were luck enough to have 0 put it straight in !!! I hope this helps you out on the location side of things !

Now as for the back lash .004” to .006” back lash is a must no more no less on these ring and pinions !
 

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Discussion Starter · #5 ·
3.91s installed

My 3.91s got installed last night. Everything went well. I am going to be gentle on it for 500 miles, but I can already feel the difference. On to the Maggie...
 

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hey fellas, i'm reassembling my rear diff. got everything together, now i just need some tq specs... the link in the 2nd post does not work anymore, so i was wondering if anyone still knew where to find them. thanks in advance! :)
 
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