My grandson and I trying to change the gear ratio from 2.76 to 3.73. We bought a Richmond kit that will allow the install of the 3.73 in a series 2 carrier. Here's the problem - nothing fits. The new bearing races are too big for the center section to carry the new pinion, the new ring gear mounting holes don't line up, there are no c clips, the axles are bolted to the axle housing. Non of the above is typical for a GM rear end. The tec at Summit says it's a Australian rear end and there are absolutely no after market parts. Is this true and what have I really got?

Jim

 

The Summit tech is probably right.

You probably have a 9-bolt rear (count the cover bolts) which is identical and completely interchangeable with the far more common 10-bolt on the outside, but utterly and altogether different on the inside. It was made by the Australian division of Borg-Warner, and parts for it are nowadays all forged only from virgin nonobtainium with about a 5% alloy of irreplacium, in spite of the fact that the new GTO/G8 uses it too (being an Aussie car itself, namely a Holden).

I'd suggest sending all that Richmond stuff back and just going to the junkyard and getting a 3.42 or 3.73 rear out of a 98-2002 Z28 or TransAm that came with a 6-speed. You'll also need new rear wheels with the 4th gen / Vette offset; but stock 4th gen or Vette wheels fit just fine. You'll need about 1¾" spacers to put the same wheels on the front.

 

It is a 9 bolt. Myself and the mechanic can't count. We found another 3rd gen rear end fairly cheap so we are going to replace the bearing, etc and go with it. Thanks for the info.

 

The 9 bolt does not need c-clip eliminators since it does not have them, better for drag racing that the 10 bolt with c-clips.

 

94-02 T56 cars came with only 3.42:1, no other axle ratio. Plus that rear axle assembly is wider, adding unnecessary weight with no advantage. Pretty sure the G8 / GTO uses a larger ring gear than the stupid 7.75"