10 bolt cover with 12 bolt ring gear

dcneric · Poncho Master!

10 bolt cover with 12 bolt ring gear

seventy2plus2 · Canadian Poncho Superstar!

Sounds to me like it's from a full-size Oldsmobile, and I'd heard that there are some diff's with a 12 bolt ring, but only a 10 bolt cover. The "12 bolt" actually is the number of bolts on the ring, but everyone thinks it's the number of bolts on the cover.

whiskeydog · Addicted!

Hi,

I worked at the The Gear Centre in Calgary for a number of years and only saw this diff a handful of times, rather rare and hard to find "hard parts" for. From what I recall they were only around a couple of years. Are there retainers at the "ends" of the axles or c- clips? That will confirm what it is. I had a 68 442 with a 12 bolt Olds with a 10 bolt ring gear, how's that for confusing?

dcneric · Poncho Master!

The axles are retained by c-clips just like a chevy. That's what is throwing me for a loop. The applications I have some experience with on the BOP type axles is that they are retained out board at the wheel.

pontorquer · Poncho Master!

Eric, Did you ask the boys on PY ? Looks to be a nice strong diff in nice shape ! Do you know what is the gear ratio ? Is there a drain plug in the middle of the cover ?

-- Edited by pontorquer on Saturday 8th of June 2013 01:32:06 PM

67Poncho · Uber Guru

(lol) Eric... Wonder if it is the same diff... I too was looking at one that is suppose to be for a mid '60's fullsize... I would like to know it's rightful place too... 41:14

-- Edited by 67Poncho on Saturday 8th of June 2013 07:21:09 PM

rabbit64cs · Canadian Poncho Superstar!

what gear ratio? how wide is the diff? sounds like it is out of 72 -74 full size chevy... ???

really odd ,, does it accept a U joint or a bolt on flange ?

4SPEED427 · A Poncho Legend!

Vince, isn't that an A body diff with those top ears cast as part of the housing?

rabbit64cs · Canadian Poncho Superstar!

Quote:

Originally Posted by speedydeedy

stoneshrink,I was wondering ,I know a 12 bolt has 12 bolts on cover and a 10 bolt has 10 bolts on cover but does this correspond to the ring gear or not?

A commonly confused subject... For the most part, the cover bolts are the same as the ring gear bolts, but there are exceptions. There was a 12 bolt with a 10 bolt cover, a 10-bolt with 12 bolt cover, and a 10-bolt with a 9-bolt cover.

The imporant thing is that the axle is named by the number of bolts on the RING GEAR, not the cover. For instance, my 73 Impala Station wagon had a 12 bolt rear axle as per the option sheet. It had 12 bolts in the ring gear (an oddball 8.75" gear) but 10 on the cover.

rabbit64cs · Canadian Poncho Superstar!

Originally Posted by joe_padavano

First, the Type O axles used in 67-70 Oldsmobiles used a TEN bolt ring gear in a TWELVE bolt housing. The question was about a 12 bolt ring gear carrier in a 10 bolt housing. By the way, the "tiny ring gear" is also 8.5" in diameter and just as strong as a "corporate" 10 bolt. It also has axles retained at the outboard ends instead of using C-clips.

Now, to get back to the original question, there was NEVER a 12 bolt carrier in a BOP A-body housing. This is probably a 9 3/8" Pontiac carrier used in the full size cars in the 70s. That housing used a 10 bolt cover. The carrier WON'T fit any A-body housings and parts are almost impossible to get.

rabbit64cs · Canadian Poncho Superstar!

Stuff I pulled off hot rodders.com

GLHS60 · Poncho Master!

I have seen these in 1971 Impala wagons. The wagons has leaf springs but as this one is coils the I suppose the sedans could have had them also. Possibly 1971-1976?? I used to be neighbors with Pete, owner of A&P transmissions in Edmonton and he told me these were the same units as Moroso Brute strength Posi's.

Thanks
Randy

pontorquer · Poncho Master!

My 1975 Grand Prix parts car had that big 10 bolt cover/housing and also my other 75 Grand Am, both had a filler plug on the cover ...

GLHS60 · Poncho Master!

Heres a link to a Demo Derby guy who talks about these 71-76 full size Chevy diffs.

Thanks
Randy

http://www.youtube.com/watch?v=jP2PFlirwPk-

-- Edited by GLHS60 on Monday 10th of June 2013 08:27:03 PM

pontorquer · Poncho Master!

Eric, did you find out about your diff ? Was this in your 69 GTO ?

dcneric · Poncho Master!

Thanks for all the feed back.

I had this laying out at my parents place and thought I might be able to use it in the goat but there are too many differences. I had popped the cover off years ago and seen the left hand bolts and ""assumed"" it was a 8.5" bop. Never seen the c-clips as I wasn't looking. Fast forward several years and I pull the diff cover off the rear that I put in the 69, a bop out of a 70 Lemans Sport, when I see left hand thread bolts and I think, cool I have a posi out at my parents place. Lo and behold I get it home and nope - no interchange going to happen.

Nothing I have found on the internet clearly defines what I have, no pictures, no reference to GM manuals, nothing. All I found are honest opinions but nothing conclusive.

CdnGMfan · Canadian Poncho Superstar!

They were referred to as the 8.75" 10-bolt. I had one in my 1977 Oldsmobile 98 Regency with 403 power. I believe in the late 1960s Pontiac used it in their U.S. full-size cars but it came in to replace the 12-bolt rear in the 1971-76 GM full size (all or most divisions). They came in selected 1973-77 A-bodies, like Chevelle wagons (only wagons, not Elkys or even 454 cars), Grand Prix & Grand Am 455s, just about all Cutlasses with 350s or better. They also came in full-size GM cars from 1977+ with 6.6-litre power, wagons, or police cars. The full-size wagons & police cars from 1977+ had a larger bolt circle on their wheels, 5", like the 1971-76 Big cars.

-- Edited by CdnGMfan on Tuesday 11th of June 2013 10:24:10 AM

dualquadpete · Canadian Poncho Superstar!

Hey guys , I'm kinda leaning towards a US Poncho with the 5x5 pattern, possible late 60's into 70's but the "C" clips are the ? don't know if they went to those later on, just a thought