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Old 03-17-2006, 03:35 AM
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I need help with ID of a 12 bolt rear end Please !

Greetings, I hope everyone is doing well. I'm almost done with a Pontiac project with a well built 462 engine and upgraded suspension. I had an 8.5" rear built for it with 3.23:1 gears and a new Eaton. This 8.5" is not a Chevy unit but I chose a BOP setup because they have the bolt in axle, rather than the C clips as well as thicker axles. Anyway, right before I'm ready to install the new rear, I come across a chance to buy a A body 12 bolt rear. However, it has a round cover on it and two old thick layers of paint. And the cover does not have the pronounced eyebrow in it. It may be an aftermarket cover, so I don't know. Anyway, before buying the 308 none posi 12 bolt. Even for a good price. I want to know if any of the casting numbers would help me determine if it's in fact a unit I can make into a posi with normal parts that are sold? I know the tubes had a stamped code on them. I also know the case had cast numbers. What should I look for?

Also, the other reason for wanting the 12 bolt is because on a 66 Pontiac the 8.5 only allows 235 rear tires without cutting up the wheel openings, where the 12 bolt will allow more room.

The owner may not want me tearing into the unit, and said it was in a Chevy from day one. But, if I do have to look inside and he allows it. What do I look for to make sure it's not something difficult to get a carrier and gears for?

I know I made this more difficult than needed, but a severe illness which is now gone left my mind far less that it used to be. So, now I have to ask questions I once knew by heart. Thanks, and good day friends.

Mike in Oregon

email rr67gto@aol.com
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Old 03-17-2006, 05:51 AM
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rear

If it was me i would not even consider buying it unless i removed the cover and was 100 percent sure it was a 12 bolt carrier in it... I had a 12 rear in my shop last summer that a guy wanted to sell me. i took the cover off and it was a 10 bolt that some one made a 12 bolt cover fit on buy drilling holes in it....This stuff is getting old and who knows what people have done to it....

If he will not let you remove the cover then he is probably hiding something...IMO walk away!!!


Don't feel bad about asking.... We are all here to help each other out.... thats what being a true "hot-rodder" is!!!!!


Keith
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Old 03-17-2006, 10:27 AM
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i think you'll find the date codes on the axle tubes, by the carrier. but yeah unless you can open the case, there is no way of verifying what is actually is. i once stumbles across one at the local trash dump... it was in the scrap pile, and i looked at it 3 times before deciging that for free, i can take a gamble on it if it is a true 12-bolt or not... turned out to be... but from a 70's camaro or something... really long tubes but leaf spring mounts..
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Old 03-17-2006, 12:12 PM
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Yeah, by all means INSIST on opening it to look it over before thinking of putting out the cash.

K-star, the axle you are talking about is a common Oldsmobile axle, it's also known as a 8.3 inch axle, PITA to find parts for and not as strong as a 8.875 inch 12-bolt.
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Old 03-17-2006, 05:39 PM
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Aw Man JVs!! Wisht I had been there at your trash dump!! Aw Mannnnn Just what I'm looking for now!!

Dave
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Old 03-17-2006, 09:27 PM
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http://www.oldsmobility.com/10bolt-tech.htm

See if it's the "O" axle pictured here.
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Old 03-17-2006, 11:37 PM
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Quote:
Originally Posted by bluesman123
Aw Man JVs!! Wisht I had been there at your trash dump!! Aw Mannnnn Just what I'm looking for now!!

Dave

it wasn't all that great... severly abused... looks like it belonged to someones scrambler/rock crawler. the brakes were shot and someone jerry rigged the parking cables to be used as brakes, it was an open diff, with 3.23 gears. and the leaf plates had several plates welded on them. like it was a piece of a frame or something. ultimately only the center section was good for anything and i used it as a trade... once i saw that they were reproducing them. but it was a really weird one... i measured the pinion and ring size and it was a true 12 bolt, but the axle code was something like a 66 or 65... but it was longer than the 71 nova 8.5 i have. so i was totally baffled by it... but got some good stuff from that trade... i even scored a 9" from a 76 bronco... and that was on the side of the road in a trash pile... center section snapped and ring gear toast, but housing and axles still good.
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Old 03-18-2006, 07:39 AM
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Thanks, now how do I tell when removing the cover?

Thanks everyone, I guess I need to tell him either I get to look at the inside, or I'm gone. Just so I don't let out that I know nothing about these 12 bolt rear ends. When I remove the cover, what am I looking for to tell me it's 12 bolt? I, thought when saying it was 12 bolt the only thing I had to do was count the bolts on the outside of the case. Now, I know that's not true. So, please advise me as what I need to look for once the cover is off?

It may take me the rest of my life, but the car will get done, and will be worth the effort it has taken. Thanks friends and have a wonderful weekend.

Mike in Oregon
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Old 03-19-2006, 03:31 AM
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i believe on first inspection you should see 12 3/8-24 RH in. bolts holding on the ring gear. that ring gear's Diameter should be 8.875", and the PINION Diameter 1.625", 30 Spline. aside from that, 10-7/8" 12 HOLES Oval Gasket Pattern.

aside from that, i'm not sure.
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Old 03-19-2006, 03:36 AM
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Sounds like an Olds to me, no splash lube eyebrow on the plate gives it away.
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