I read through the FAQs concerning swapping the ring and pinion gear and while there is some good information in there I am still little unclear about a few things. I have a 68 400 w/factory, still running the stock 2.56 setup. For 68 the Firebird used a 8.2" 10 bolt setup, and the 10 bolt refers to the 10 bolts which hold the ring gear in place - do I have that right? Also, I see the BOP ring and pinion are not compatible with Chevy - is that correct?
I also see some references to gear housing limitations. My problem is that I have seen 2 different limitation guides. First one said you can go up 1 step meaning that from 2.56 I can go to 2.78 without housing mods. The next step would be good for 2.93 & 3.08. and so on. The second guide I found said from 2.56 one can go to 3.23 without housing mods. Which is correct?
I see lots of gears being offered for 3.36 and above but I am targeting 3.08 (in conjunction with a THM400 overhaul). Where can I find a hi quality BOP compatible 3.08 ring and pinion? Thanks.
For 3.08 gears, you will need to find a good used set. There are plenty out there. I don't believe they make any new gears for 8.2 BOP's lower than 3.55 or maybe 3.36. The part of the rear that is gear ratio dependent is the carrier, which is the part that the ring gear bolts to. There are different carriers. I found this breakdown for carriers when I googled: 8.2″ BOP 2.76 & down / 2.94 to 3.23 / 3.31 (3.36?) & up. Maybe just find a 3.08 BOP rear and use the gears and carrier. Open rear ends are pretty plentiful and cheap and the internals are pretty interchangeable for many years of pontiac/olds/buick 8.2's. If you are looking for a good condition limited slip (Safe-T-trac) that could be a harder and more expensive find. They only make aftermarket posi carriers for 3.36 and higher.
The term "10 bolt" refers to how many bolts in the cover.
If you don't care to keep it 100% original with the BOP rear end, it might be cheaper to find an 8.5" GM rear end from a 72 - 75 Chevy Nova or Pontiac Ventura, It will bolt right in with only shortening the driveshaft one inch. They are very plentifull and cheap, lots of aftermarket parts to make it very strong if needed, but it is all most as strong in stock form as a 12 bolt. I have one in my 69 with 3.42 gears and TH-400 and it is just perfect for me on the freeway
I did the same rear swap in my car last year. As it was already mentioned if you don't care about leaving it stock, you can get a complete rear end with a 3:08 ratio or close and you're done, easy change over. If you chose to retain originality you won't be able to use your existing carrier, and buying a Yukon or similar complete set-up has it's disadvantages according to many reviews out there. I ended up leaving my carrier in it and used a spacer to get the new ring and pinion to align. Spacers are offered here: https://www.amazon.com/Bolt-Vette-Ring-Spacer-Bolts/dp/B00SDI83Y6. Don't believe the hype out there that claim spacers will come loose. That's BS. You do have to keep in mind that the change over takes expert knowledge, takes time and lots of precision touches to get clearances correct. And you will have to locktide everything to keep things from ever loosening up. Took me 2 weekends to do, taking my time and double checking everything before putting it all back together. It's a fun job, don't expect any huge gains unless you go up to 3:55 plus.
The only thing I would add to the 8.5 Chevy conversation is that they are 1 inch narrower then the Pontiac units. I actually owed a 68 with a 8.5 from a nova and even though the wheels were only sucked in a half inch per side it wasn't a good look and you could really notice it. Of course that was running stock 14x6 rally wheels, if going with aftermarket wheels this is easily fixed by altering backspacing. I ended up changing the rear and when I measured to verify sure enough it was 1 inch narrower. Pontiac started doing this to there cars starting I think around 59 or 60 and marketed it under the name Widetrack. Also when using the Chevy rear they used a smaller u-joint but the aftermarket offers an adapter joint to solve this if you use a Pontiac shaft. And yes you are correct the number of bolts 10 or 12 is what holds the ring gear to the carrier but also happens to coincide with the number of cover bolts making it quick and easy to identify between the two with a quick peak under the car. oops I see I responded to bob s this was meant for Texas bird.
Last edited by barnbird; 01/01/2104:08 PM. Reason: blindness