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I think this was discussed about 2-3 weeks ago in engine and drivetrain do a search for 12 bolt and your answer is bound to be there.
 

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I have a 70 Olds posi unit in my 70SS. I can tell you the bolt pattern for the cover is slightly different, but it is hard to tell. Brakes and brake lines are the same. All internal components are different, i.e ring&pinion etc. I rebuilt mine with a 3.90 gear set that I got from Randy's Ring and Pinion. Very helpful folks.
Good Luck.


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Darryl
Red 70 SS 454
 

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I bought some kind of 12-bolt posi years ago. It had the same brackets as the Chevelle, so it bolted right in, but I couldn't find the correct gaskets and parts. Real frustrating (I thought it was a Chevy).
It didn't have the C-Clips (Axle bearings were pressed on) and it had a piece of flat metal bent into an S-Shape that provide the pressure for the clutch plates, no little coil springs.
Finally found it was for some mid-70s or early 80s Buick or Olds, and only came with 2 ratios, like 2.80's and 3.00's.
 

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Lucky3,I found out the hardway about an Olds 12 bolt. Any 68-72 GM A body rear end assy. will bolt into your Chevelle,but If I were you I would find a Chevelle or Monte Carlo rear. I'm sure parts are more plentiful.
 

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The Olds 12 bolt is not the same as a Chevy 12 bolt. The Olds 12 bolt is an oddball, it is a 12 bolt cover but the gears are the same size as a 10 bolt. Stay away from the Olds rear end, people often think all 12 bolt A body rear ends are the same, they are not.
 

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also the drive yoke may be different!I would not go as far to say stay away from it,,just make sure it has a twelve bolt carrier,also some have heavy axles that are hard to find,more splines.but this could be a plus,remember just because the cover says twelve bolt,the carrier may say 10 bolt!this,stay away from!that is what the last post was saying-67RAT member #199

[This message has been edited by 67RAT (edited 01-29-2000).]
 

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To answer the specific questions originally posted:
No, they are not the same, and no, a 12 bolt chevy posi will not fit.

BTW, if you do buy it, I would be interested in buying it from you after you find out it won't work in your Chevelle. Let me know what you want for it, anything under $100 of course. (kidding)

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70 & 1/2 RS Camaro
SB406 & M20 4spd
9" Rear
70 Malibu
SB350 & TH400

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Driveline Technician
 

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The only Olds 12 bolts that are the same as Chevelle units are '68-69 ones from F-85 cars, and 442's. The others are completely different. I know I'll get some arguements about this, BUT, pull up Richmond Gears webpage, or look in the catalog. It's posted right there. You will have to look for C-Clips, or bolt in axles to be absolutely positive about the one you buy. You want the C-Clip style.These are the only years that are the same!Jeg's and Summit state the same in their Richmond gear advertisement.I had an Olds guy tell me this, and he knows his stuff. Kinda like Lemans rears in ' 70 Monte's, anything was possible.

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1972 Malibu (1 st. car) Project waiting to happen
Team Chevelle # 427
A.C.E.S. # 1282
 

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They are completely different. The Olds 12 bolt is only bad because of the limited replacement parts. Posi units used are expensive and somewhat rare. I have a numbers matching 68 442 with the original Olds 12 bolt. I did have a 69 hevy 12 bolt in for a while but put the original back in. The 68-70 Olds 442, cutlass, and etc. could have either rearend put in, depending on what was available on the line. Even the
W-30 optioned cars could have had the Olds rear. BTW, I also have a bright red 67 chevelle, Built BB, 4 speed, 12 bolt posi, black interior sitting next to my white with red fender striped 68 442.
The world could be a terrible place.
Great site guys!
 

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Actually which axle a 68 or 69 442 or Cutlass had depended on where it was made. The ones made in the U.S. used the Olds 12-bolt in them, but the ones built in Canada used the Chevy 12-bolt (just like Canadian built Pontiacs had Chevy engines). That is why the Chevy 12-bolt is listed by Richmond as being in the Olds cars.

Joe is right about these axles, they are good units and plenty strong, but parts availability is terrible! Best stick with the Chevy 12-bolt and leave dealing with the Olds 12-bolt to the Olds boys.
 
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