I looked in the tech section and couldn't find the answer to this question. Is there any way to find out if my 72 Cutlass has 28 spline axles without yanking them out? My gear ratio is 2.73 right now, but want to change it to 3:23 or 3:42.

Also, I want to put in a posi. But is 72 an 8.2 or 8.5 ring gear? I know that its a ten bolt rear end, but need some help deciding if I should go with auburn, wheaton or GM carrier. I've heard really good reports on auburn. Anyone got any tips or information that would help?

 

If your rear is org to the car then its an 8.5 with bolt in axles. Just get a posi carrier out of and '71-87(maybe more?) 8.5" rear an your good to go. Good places to look are old cameros and firdbirds, station wagons, pick ups. Or the after market is loaded if you want to go brand new. The 8.5" is a good rear and it can take a beating. Buddy if mine has one behind a buick 455 all stock running 11.80s for years and hundreds of passes down the track. If your looking for a rebuilt org contact Brain Trick (507olds)
on ROP he'll set you up. JKaz

 

Allen, do a search on threads about posi's as I know this has been discussed before. I really like the 8.5 corporate posi's and think your fortunate to be starting with a 1972 housing that came with the 8.5 corporate rear. John

 

Thanks guys, this is just the info I was looking for to start. I've seen lots of posi carriers on the web for really good prices. Most are auburn, but every so often there's a GM series 2 or 3.

Can either of you tell me the difference between an 8.5 and 8.2 ring gear besides the obvious .3? Probably need a different pinion too, right? Is the 8.2 for an "O" rear end? I've heard all sorts of references to the 8.5, 8.2 and 7.5. I believe 7.5 is the corporate rear end for G body and isn't interchangeable with my car, right? But are the 8.5 and 8.2 interchangeable?

John, can you give me a lead on the searches for posi in the threads, I'm not exactly sure where to start. (Are you the John in Oregon who lives next to the Sasquatch pit??)

 

Hello Allen
Yes it's me, and the big hairy one has been scrounging parts somewhere else lately, I haven't seen him since the incident with the 1971 Delta.

I looked through the threads and didn't find what I was thinking about. I also checked the wiki site and it still didn't have the details I was thinking of.

Here's what I remember: The 8.2 is a different design, I believe a cone style unit. Because of that it's not easy (or possible?) to rebuild them. They are also not as strong as the 8.5

The "O" style from 1967-70 was an 8.5 but parts like the ring and pinion are not readily available.

The corporate 8.5 was used for lots of years and in lots of GM cars and trucks. Like JKaz said you can find these a whole lot easier than the other older styles. Probably because of that there's more aftermarket parts for them too. I also believe they can be rebuilt. I've got several posi rear ends for my project cars, but only a couple are the newer corporate 8.5 units.

So for your car, you can find the "guts" of an 8.5 posi in the bone yard in something other than an A-body and have it installed in the rear end of your car. You can also have it rebuilt or change gear ratios in the process. Any deeper questions you may want to check with Monza (?) as he's the resident expert on rear differentials. John

 

www.jdrace.com
Look in Jim's I.D. section.

When looking for a carrier, make sure it's a 3 series. if you find a 2.41 posi rear or 2.56 posi rear, the carrier won't work with 3.08-3.73 gears.
The ring and pinion are a matched set. You shouldn't mix and match them because they all have their own meshing patterns.

Also, Jkaz is right about camaros being a good source. Just stay away from the 2 series camaro carriers. Be careful, because in 85 and up or so, a lot of them were 30 spline.

 

There's nothing wrong with an open rearend on a street car. Actually, I like it much better.
My daily driver could run high 13's all day with a 1 legger 3.08 open and regular old 235/R15 street radials.

 

 

John, your memory is pretty good, from what I can see! Did want to mention that the 8.5s are *generally* stronger than the 8.2. By that I mean that the vast majority of the 8.2s had 2 pinion carriers. But later '67 could have 4-pinion carriers that were as strong as any 10-bolts out there. These units were used in the '67 W-30s in lieu of the new 12-bolt/10-bolts Olds rears.
Not that it matters in this case as Allen is going for an 8.5.


Ask Jim directly (email or his forum), as he is quite an expert and can be very helpful.

 

Ok, got my 3:42 ring and pinion. Its stock GM and shows very little sign of wear. (12 teeth on pinion, 41 on ring) Still looking for a used posi, or new one for a decent price. LMK if anyone has something.

2blue442 (John), you got anything kicking around?

 

Sorry Allen, the only thing I have that would work with your 1972 housing and 3.42 gears is planned for the 1964 Cutlass 4 speed project car.

If you could come up with a type O housing I think this would be a good price and worth paying to ship the guts anyway.
https://classicoldsmobile.com/forums...si-3-42-a.html

Have you checked out Craigslist from various towns? If you found something close to me I'd be willing to pick it up and ship it to you.

Supercarsunlimited sells new posi carriers, if you haven't priced his yet you might check it out. Over the years I've bought several things from him and always been satisfied. John

 

 

Hey, here's a question:
Saw a bunch of B Bodies at the boneyard, but no A bodies that had posi. A couple of the B Bodies do have posi. The cars are up off the ground so its easy to check. Will a posi from a (year range 78-84) Delta or 98 be the same carrier as the one that goes into the A bodies?
If it is then my search might be over. Just gotta go pull the wrenches

 

You will have to look at the carrier casting numbers or the ring gear count stamps.

Carrier 410409 is for 2.56-2.14 ratios.
Carrier 410408 is for 2.73 and lower. (higher numerically)

You need 410408 for your 3.42 gears.

 

Or maybe one of the bookworms here has a book of RPO trunk codes that you could look at on the trunk lids instead of getting all full of gear lube.

 

I don't think the B-body carriers interchange; I believe that they are 12 bolt ring gear; I had a B-body carrier and I couldn't use it because of that fact, so I eventually sold it to a guy in the 'Shwa' with a '68 Delta...seems the axles are different too... 3:42 axles use a 31 spline shaft

 

Thanks for the info on the B Bodies. No point spilling diff fluid if they won't fit. Guess I'll have to keep looking.

 

Thanks. I'll use that on my next web search. If I find any A body donors at the boneyard I'll be taking this number with me. Usually an easy spot for posi with the tag and wheels off the ground. BTW it's probably easier to GET a numbers matching poker hand than get a car just the way you want it. Seems like everything changes. LOL Love your signature line.