Hi guys. I thank you in advance for any help you can give me! A friend of mine has a nice 12 bolt setup in a 71 skylark. I am pretty sure the lengths are different correct? Are the locations for the trailing arms the same and all of the other suspension components does anyone have any idea! I can pick this rear up for pretty cheap and it would help out my lower budget build thanks to this wonderful economy. Thanks guys. Paul

What did the rear originally come out of ?

71 skylark

OK but the 71 Skylark didn't come with a 12 bolt -per the Hollander Interchange Manual.
Now the 70 had a rear with a 12 bolt cover but 10 bolt internals -known as the "type O".
See if you can get the code on the front of the passenger side axle tube.
Or see which it looks like:
http://www.oldsmobility.com/images/reardiffsID.gif

ok that news is going to make this even more interesting. Lets suppose we are talking about a 71 gto. What are the differences between the 1966 chevelle housing and the 1971 gto housing as far as mounting alone. I am not interested in originality nor inner gears. Again thank you greatly for your help mike

71 GTO could have the 12 bolt or the 8.625 10 bolt.
Would have been 1" wider than the OEM 66 rear and does bolt right in.
Might need a crossover u-joint depending which yoke is on the rear.

Alright so i guess what i am asking is if this 71 skylark in question has the mounts in the factory locations for rear, the control arms should bolt up to my rear and just the length will be a little off? I just climbed under my chevelle and measured 53 . 5 inches from backing plate to backing plate. Sound about right Mike?

Yes.
You still might want to verify it's actually a Chevy 12 bolt and not the O-type rear.
If you get the axle code and we'll know what year/rear it is - not just for an originality check.

If it were an o type, a moroso brute strength carrier wouldnt fit in it if it had ten bolt internals correct?

Right.
The o-type doesn't use c-clips either ,the axles are retained at the axle bearing.

Hmmm all skylarks from 70-72 came with 10 bolts. Even the stage 1 cars. The stage 1s either came with a 3.42 or a 3.64 posi and they were all 10 bolts. Im sure it was out of something else :)

Agreed but it wouldn't have a 12 bolt cover.
Without the code ,seem's it may be a Olds or GTO rear as previously posted ,or possibly something else altogether.

Alright so i guess what i am asking is if this 71 skylark in question has the mounts in the factory locations for rear, the control arms should bolt up to my rear and just the length will be a little off? I just climbed under my chevelle and measured 53 . 5 inches from backing plate to backing plate. Sound about right Mike?


If its bolted in the 1971 skylark, then YES, it will bolt up... Mounts will be the same, with the differences being where the wheels sit...

Don't Be Confused!!! If it's an "Oldmobile 12-bolt" rearend, then it is NOT the Heavy Duty (some might say "high performance") rearend that the Chevy 12-bolt is...

The Chevy cover is stamped with the "inverted V" to aid oil drainback to the carrier bearings... The Olds covers didn't feature this design ( AFAIK).

Just because it has 12-bolts on the cover, doesn't mean its a good performance rearend... As mentioned many times, the "Chevy 12-bolt" uses 12 ring gear bolts (as well as 12-cover bolts), and has the 8.875" diameter ring gear. Those pieces are where are reputation for strength comes from... the Olds rear might have 12 COVER bolts, but what good does the amount of cover bolts do??? Unless you NEED a new rearend (yours is missing or broken), its probably not a great choice...


As for the GTO, supposedly, the 455-powered GTOs got the "Chevy" 12-bolt, while the others (400s), got the regular Pontiac rearend...

Thanks for all the help guys. It does have a moroso brute strength carrier in it and I will get the tag and or stamped #,s off this thing to confirm. I never knew Gm had so many different housings. I thought it was always either 10 bolt single or posi and 12 bolt single or posi and thats it. Originality is not a big concern to me and I am going to drive this car a lot on weekends and have fun with my son with this car hopefully attending a lot of car shows. It is going to be a frame off with a lot of new sheet metal and black on black. Pretty peppy small block going in that went 11 : 50 s in a nova on pump gas which is the great thing. Cant wait to get further along on this project. New quarters and a ton of new sheet metal in boxes in my garage! Thanks again for all your help guys!