I 'll try to make this as concise as possible. 5 years ago I put a stock 8.5" gm posi unit in. I never touched the pinion, simply swapped the carrier. I bought the 8.5" carrier based on the diff cover. The installation went well, no problems. Fast forward to today. I wanted to change to a 3.73 ratio. So I bought a set of richmond 8.5" gears and the richmond 8.5" install kit. The 8.5" ring gear fit on the carrier no problem, nice and tight, same as the old one. I pulled the pinion out and realized that none of the new 8.5" bearings fit. The yoke is the wrong size as well. I figured Richmond sent me the wrong install kit. Then after more digging and looking at some posts here, I realized that my housing is an 8.2", as is the pinion. But it's been mated fine to an 8.5" ring gear and carrier and runs great. The axle code is GNC 059 and it uses a 1 1/8 pinion nut. Does this make sense? Is the business end of a pinion on an 8.2" the same dimensions as an 8.5" pinion? So that this would work? ANy insight would be greatly appreciated.

The inside diameter and bolt pattern on the 8.5 ring gear is the same as the 8.2. You can bolt the 8.2 ring gear to the 8.5 differential, but the pinion is not the same. You can not mix gears, ANY gears. The pinion gear is mated to the ring gear at the factory and can NOT be run on ANY other ring gear, even if they are the same ratio and for the same rear end.

If you somehow managed to get an 8.5 differential into the 8.2 housing then you must have bolted the 8.2 ring gear to it. My guess is that you actually put an 8.2 differential in your rear end thinking that it was for an 8.5. The cover off of an 8.5 will fit the 8.2 housing perfectly. I have 2 of the 8.2 Camaro rear ends that have 8.5 covers on them. Anyway, the parts that you have will not work in the 8.2. You need to return them and get 8.2 parts.

Thanks, I expected it was something that simple.

Do you have a picture of the posi, or does it have a casting number on it? I can tell you what you have if you can get this information for me.

The 8.2 uses 3/8 bolts and the 8.5 uses 1/2 bolts to fasten the ring gear to the carrier.
My bet you bought a 8.2 carrier. No 8.2 and 8.5 parts interchange.

Dave

The 8.5 uses 7/16 bolts. The 8.2 gear will bolt to the 8.5 differential because the bolts are smaller. The 8.5 gear won't bolt to the 8.2 differential because the bolts won't fit through the holes. There are a few of the 8.5 and 8.2 parts that will interchange, but not many. Axles, some bearings and shims, brakes... I have heard of a few people that installed 8.5 differentials in the 8.2 housing, but I think they had to do a few modifications to make it work. I haven't tried it myself.

After some more examination, and a couple whacks from the palm of my hand to my forehead, turns out I do have an 8.5 carrier, but everything else is 8.2. Thanks for the responses. Somewhere along the way I convinced myself I had an 8.5 for some reason. Anyway, the correct replacement parts are on their way from Summit. Thanks for the help.

8.5's also have reverse threads that hold the ring gear on the carrier.


aaron