# what 12 bolt can I put in my 68



## jamon8 (Jul 13, 2013)

I have a 68 gto and the factory 10 bolt locked up when I towed it to my new place and I am not gonna spend money on that turd.


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## Instg8ter (Sep 28, 2010)

Any out of a 64-72 A-body will bolt right in, stay away from the Olds 12 bolts they are different from the chevy ones. The Pontiac 10 bolt is a good rear end up to around 450HP. 12 bolts are getting harder to find and they fetch around a grand for good used. Moser can make you one new for a few grand, or for high HP use they will build you a ford 9" to fit your Pontiac. Where you located i have a chevy 12 out of a 69' chevelle with 3:55 gear i may be putting up on craigslist if work slows down. Welded tubes, Strange axles, will need a carrier as its has a mini hub in it now (not good for street use).


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## GoatGuru (Oct 1, 2013)

Instg8ter said:


> Any out of a 64-72 A-body will bolt right in, stay away from the Olds 12 bolts they are different from the chevy ones. The Pontiac 10 bolt is a good rear end up to around 450HP. 12 bolts are getting harder to find and they fetch around a grand for good used. Moser can make you one new for a few grand, or for high HP use they will build you a ford 9" to fit your Pontiac. Where you located i have a chevy 12 out of a 69' chevelle with 3:55 gear i may be putting up on craigslist if work slows down. Welded tubes, Strange axles, will need a carrier as its has a mini hub in it now (not good for street use).


 there are two versions of the 10 bolt for Pontiacs there is the standard 10 bolt and there is the super duty that has the 12 bolt guts look to make sure. The super duty is very tuff and you can put 12 bolt guts into your 10 bolt a lot cheaper then finding and or Buying a 12,Unless that is the look you want. But any 12 bolt from any A-body car from 67-72 will fit.. the 67 is about a a quarter inch shorter both sides of axle and will work and it will give you more room for rubber I have a Olds 12 bolt from a 1967 442 under one of mine... I can run a wider tire.:cheers


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## GoatGuru (Oct 1, 2013)

64 to 67 are a shorter axle not as wide as the 68,Measure flange to flange should be AND NO DONT STAY AWAY FROM OLDS really the olds 442 rear ends are just as strong and yes they are different Internals and brake the pads are almost imposable to find as with a good gear ratio. But you can remove the Olds pads and inner guts and put in what ever you want. there interchangeable. You will just have to remove every thing and swap every thing from one to another. And if running a low gear some machine work will need to be done inside housing for clearance of ring gear. But don't walk away from one if it is a good price. A olds 12bolt core from 1967 is a grand for a core alone and are not easy to find there rare.. there is one here in Seattle 1967 442 rear end 3:08 none posi $2400.00 any ways happy motoring..


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## BearGFR (Aug 25, 2008)

GoatGuru said:


> AND NO DONT STAY AWAY FROM OLDS really the olds 442 rear ends are just as strong and yes they are different Internals and brake the pads are almost imposable to find as with a good gear ratio. But you can remove the Olds pads and inner guts and put in what ever you want. there interchangeable.


No, they aren't - and no, you can't.
Check this page:
Olds FAQ -- Differentials

Note this particular section:
N-bolt Terminology
The tern "n-bolt", as pertaining to the rear end of the car, refers to the number of bolts retaining the ring gear to the carrier inside the differential. Fortunately (or unfortunately), this number usually corresponds to the number of bolts holding the differential cover, so you can usually tell whether you have a "10-bolt" or "12-bolt" rear from the number of bolts on the outside of the casing. This is independent of the rear end gear ratio. 

The Type O (Oldsmobile) 12-bolt rear ends use a smaller ring gear than the Type C (Chevy) 12-bolt, resulting in lower strength. The good news it that the Type O units retain the axle shafts at their outboard ends, while the Type C units use the infamous c-clips at the imboard end. This is why you see C-Clip Eliminator kits available for the Chevy axles. Also the Chevy rear has a "scalloped" cover where the Olds is smooth. 


N-bolt Differences
An Olds 12 bolt rear end is not a "true" 12-bolt. It may have 12 bolts on the outside cover, but it is a 10 bolt gear on the inside. The more common type "C" is very much different than the type "O". 

A "true 12-bolt" has come to mean a Chevy c-clip 12-bolt rear. Oldsmobile 12 bolt rear ends differ from Chevys internally. In other words, the guts of a Chevy rear end will not fit in an Olds rear end housing, and vice versa. The phrase, "more like a 10-bolt", is usually talking about the size of the ring gear and/or strength of the carrier. The guts of a 10 bolt would not work or fit in a 12 bolt, and vice versa. There are differences between the 10 bolt and the 12 bolt both internally and externally. 

Note also that there are two different ring gear carriers, one for 3-series ratio gears and one for 4-series gears. 3 series and 4 series carriers are for the 12 bolt Chevys. The difference is the dimension from the ring gear mounting flange to the pinion centerline, due to the larger diameter pinion required for the lower numerical gear ratios. A set of 4-series gears can be installed in the 3-series carrier with a spacer and longer bolts (not desireable due to reduced strength), but the reverse is not true. 

The ring gear size is the size of the largest gear, parallel to the wheels. A 12 bolt Olds has a 10 bolt carrier that measures 8.3", whereas a 12 bolt Chevy has a 12 bolt carrier that measures 8.8". A 10 bolt Olds out of a 1971 has a 10 bolt that measures 8.5". 1968 and 1969 10 bolts might have an 8.2" ring gear. Starting in 1970, 10 bolts might be 8.5". Newer 10 bolts found under the last RWD Cutlass and Chevy are little 7.5". 

Oldsmobile bolted the axles from the inside of the housing, whereas Chevy used c-clips. As for Buick and Pontiac, they used different types of posi actuating items called "cones" and "spools", whereas 12 bolt Chevys and Olds used what are called "clutch packs". 

Type "O" Oldsmobile Rear Ends
The biggest weak spots in Olds rears are the wheel bearings and the availability of parts. Positive axle retention is good, but put in the new "updated" style wheel bearings for more strength. 

Gears for the Olds 12 bolt rear are hard to find. The "O" was only manufactured for 2-3 years. So there isn't enough call for someone to start casting and machining new cases. While posi cases are not available (as far as I know) rebuild kits are. Unless the case you have is outright cracked or otherwise junk you should be able to rebuild it. 

Bear


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## GoatGuru (Oct 1, 2013)

BearGFR said:


> No, they aren't - and no, you can't.
> Check this page:
> Olds FAQ -- Differentials
> 
> ...


And Yes you can.. One of my 68 gtos have a 67 olds 12 bolt and I have had the carrier changed over to a Pontiac safety track with 3:90s that came out of a 1969 Don't tell me it wont and don't it will and dose. My Uncle that owns Six company's that deal's with rear ends and drive lines here in the North west say's other wise .DO YOU do rear ends day in and out? I Don't think SO MATTER OF FACT I KNOW SO. My 67 olds axle has had every thing inside removed and has had a posi from a 1969 pontiac 8.5 put in side And Yes the Bearings have been changed to a heavy duty same as a BOP 12 bolt. Things you can do when you own a Machine shop and family do other thing's automotive. And yes the inside of the housing has been machined for a bigger gear and carrier.
So like I said Don't tell me Bear. But were just a bunch of tree huggers up here in Oregon we don't know any thing.. :cheers....


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## BearGFR (Aug 25, 2008)

I'm posting 3 photos. The first two are both Olds "Type O" axles. They have 12 bolt covers, but inside there are only 10 bolts mounting the ring gear to the carrier, and the ring gear is 8.5 inches in diameter. The last photo is of a 'real' GM 12 bolt. It has 12 bolts mounting the ring gear to the carrier, and the ring gear is 8.875 inches in diameter. None of the internals of these two axles is the same, or interchangeable. Plus, the GM 12 bolt uses the infamous c-clip axle retention system, the Type O does not. The only similarities between them are that they're both GM, they were both sometimes installed in some A-body cars, and they both had 12 bolt covers.

People sometimes mistake the Type O for a 12-bolt because they're counting cover bolts, but the bolt count that matters is on the inside - the number of bolts holding the ring gear to the carrier. The Type O was only made for a short time and parts for it are very hard to find. Strength wise, it's roughly equivalent to the "normal" 10 bolt, and not nearly as strong as a real 12 bolt.

Bear


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## geeteeohguy (Feb 2, 2008)

In addition, I'll add that Goat Guru is mistaken on axle specs for the ten bolt 8.2 units. The '64-'65 axles are 1/2" shorter than the '66 and up units. '66 and up have axles that are 1/2" longer. BTDT, many, many times. jamon, the later 8.5" Pontiac ten bolt is a very strong rear end, better than the Chevy 10 bolt, with better axles, and is easier to find. For some really informative information/reading, look up Ol'Pinionhead and his posts on the pyforums. He wrote the book on these rear ends, pretty much. Good luck.


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