# Posi



## Pontiacpurebrred (Jun 22, 2011)

So, 69 Custom-S/LeMans/Tempest/GTO 
Currently has a peg leg drum brake rear end. 

I am (as always) searching Craigslist, currently for a rearend. What are my options for fitment (within reason). I am thinking 68-72 Pontiac, Olds, Buick, Chevy stuff like Firebird, Camaro, Chevelle, 442, Skylark ... right?

Other options?


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## Thumpin455 (Feb 17, 2010)

70-81 Firebird/Camaro wont work, they have leaf springs, completely different way to mount the axle, and they all had 8.5 or 12 bolt rears. Only a very few 72 A bodies got 8.5" rears, most from 64-72 were 8.2 with cone clutches. The cone clutches are not rebuildable, and these rears are hard to find in good shape with a locking diff. The gears from a 67-69 Firebird/Camaro will work but the housing will not.

Oldsmobile had their own rear end for a while with a 12 bolt diff cover, usually they had highway gears. One I have is endowed with 2.93 and a locking diff, the other is an open peg leg. They have ten bolt ring gears despite the 12 bolt cover. The benefit of these rear ends is they have clutches in them like the 12 bolt and 8.5, not the cones, so they can be rebuilt.

If you are looking for a rear end you know will fit, and you can build with a locking diff (posi) find a 12 bolt from an ElCamino, 69-70 Monte Carlo, or Chevelle. SOme GTOs had them but its unlikely you will find one out of a car, but hey it happens.

It will cost you between $900 and $1400 to rebuild an axle you find from another car, that is if you can set up the gears and press the bearings on yourself. You have to know exactly what you are doing with rear ends or you have expensive junk very quick and easy. The 12 bolt under my 70 was rebuilt with an Eaton diff, 3.42 gears, new bearings everywhere, and without the brakes being rebuilt it was $1100. At that price its getting close to where its just as cost effective to by one from Strange, Moser, DTS, or a 9" from Currie. If you cant set one up yourself then it makes sense to save up the $2k and just get one with the gears you want already installed.

You wont be breaking a 12 bolt for certain, and its doubtful you will break a 10 bolt since you dont plan on drag racing with slicks. A 9" would live forever and make gear changes easier. Sometimes you can find one ready to go, most times you find them needing rebuilt.

Chevelle, Cutlass, LeMans, and Skylark 66-72 is what you are looking for, the 64-65 rear ends will work but they are about an inch narrower so they move the tires inward about half an inch. They are also harder to find since fewer of them were made.


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## ALKYGTO (Mar 29, 2010)

^ Spot on. Don't forget 12 bolt Chevys also have those crappy C-clips and that they use the axles as the inner race for the outer axle bearings.

OP, just weld up the spider gears if you want a "posi". :lol: JK


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## Pontiacpurebrred (Jun 22, 2011)

SO if the 71 Safari (my 455 donor car) has posi doubtful it will work?


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## ALKYGTO (Mar 29, 2010)

Prolly not. Completely different chassis so I doubt it will bolt in.

All you can do is measure, measure, measure. Probably too wide and the attachment points will be all wrong.


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## BearGFR (Aug 25, 2008)

Pontiacpurebrred said:


> So, 69 Custom-S/LeMans/Tempest/GTO
> Currently has a peg leg drum brake rear end.
> 
> I am (as always) searching Craigslist, currently for a rearend. What are my options for fitment (within reason). I am thinking 68-72 Pontiac, Olds, Buick, Chevy stuff like Firebird, Camaro, Chevelle, 442, Skylark ... right?
> ...


I've got a 10-bolt posi that I was originally going to use in my GTO until I decided to build it "stronger". Supposedly it has 3.23's in it, but I've never had the cover off nor have I checked the condition of the posi unit. All I did was clean it up and paint it. I've also got a set of factory boxed lower control arms and factory rear sway bar. The control arms have brand new uerthane bushings in them, and also have been painted.

Bear


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## Pontiacpurebrred (Jun 22, 2011)

BearGFR said:


> I've got a 10-bolt posi that I was originally going to use in my GTO until I decided to build it "stronger". Supposedly it has 3.23's in it, but I've never had the cover off nor have I checked the condition of the posi unit. All I did was clean it up and paint it. I've also got a set of factory boxed lower control arms and factory rear sway bar. The control arms have brand new uerthane bushings in them, and also have been painted.
> 
> Bear


Bear you are my hero. PM me and we can talk turkey.


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## Rukee (Feb 8, 2007)

Just drop in an Auburn limited slip carrier, swap your gear over and instant POSI.


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## xconcepts (Jan 4, 2009)

I've got a 10bolt 2.56 off a 72 buick and a set of 3.23 with carrier, you'd need to add a posi but probably cheaper. It was on my 66 until about a year ago.


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## geeteeohguy (Feb 2, 2008)

'64-'72 will all bolt right in. Stick with BOP for ease of axle servicing, etc. The neat thing about '64 and '65 housings being an inch narrower is that you can get WIDER TIRES stuffed under the rear wheel wells. Take a look at Rukee's '65. Not to shabby.....


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## jetstang (Nov 5, 2008)

I put a 66 Chevelle rear in my 70 and 15X8 rims with 275s in the wheelwell without rubbing at all. It's an open rear with 3.36 gears, going to do the posi sometime, but my little 350 doesn't need a posi, just a cruiser, well slow.. And I don't like it slow, but I have faster cars so it's OK..


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## geeteeohguy (Feb 2, 2008)

I agree, Jet. They don't _all_ have to be racecars. Went to the Montery Historic races yeasterday in the '67 with the lazy 2.56 gear....340 mile round trip, and got about 20mpg at 70-80mph.....pretty hard to do _that_ with a performance axle ratio!!! going fast off the line is what the "other" car is for!!!


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## Instg8ter (Sep 28, 2010)

I am not doing posi til over the winter so i decided to see how the 2:56 peg leg would work behind the 463 auto to get a feel for what gear i will get....i am amazed at the gas consumption to say the least, Like GeeTee said. It thumps along at 65-70 right at 2000RPM yet can lay a 25' patch off a 20 roll with 4 people in the car without even breaking a sweat...that's having your cake and eating it too!....i think i may go to 3:08 tops on the posi as it should hook a bit better than the one legger.arty:


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## geeteeohguy (Feb 2, 2008)

No Doubt. There's a lot to be said for a classic car you can actually drive often because it gets decent mileage and can cruise comfortably with high speed traffic....a car you can pile friends and family in and actually drive somewhere! With all the torque even stock Pontiacs have, never mind a stroker motor, a short geared rear end is not needed. I think with an automatic and a stroker motor, and no overdrive, a 2.93 or 3.08 posi would be about perfect....preferably a 2.93, IMO.


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## jetstang (Nov 5, 2008)

For a cruiser, I would go with some 2.** gears, and put a posi in for the cool burnouts! Saves money on buying an OD tranny or gear Vendor OD unit. It's not fun trying to run 70 at 3000 plus RPMs. I am old school and want the gear, but 10 MPG gets old with the engine screaming and my car isn't that fast. Might as well make it a burn out machine and respectable highway cruiser.. G8ter, throw a posi in that rear, unless your taking it to the strip. The late 70s TAs had 2.** gears and a posi..


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## Instg8ter (Sep 28, 2010)

thats what i am thinking for cost sake Jet....no way around spending 2k on a new or re-build unit, so since i like the 2:xx gears i will probably get a posi unit for this rear end since i don't plan on beating it into the ground at the track and love the gas mileage and manners of it. really glad i waited to get a feel for the car before dropping that kinda cash on a big gear i would not be happy with in the long run.


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## Thumpin455 (Feb 17, 2010)

I love my highway gears! In both the Trans Am/Formula and in the GTO/LeMans. Put enough torque ahead of it and its going to be a quick car regardless of the gears. My favorite is 2.93 or 3.08 with an OD trans, deep first in the 2004R helps a bit, and the OD gives you 1700rpm at 80mph cruising. With a 455 you have more than enough grunt to pass without dropping a gear. I think even a 400 could pull those gears well.


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## Pontiacpurebrred (Jun 22, 2011)

I don't know yet what I am going to do about the rearend for mine. I am like the clown at the circus with all the plates spinning on the ends of the long poles. I have the car half torn apart, I have parts all over the place and now I have 2 (TWO) engines sitting in half my garage. (Can you hear circus music playing in the background?) I need to get back to one thing at a time. 

I think I will leave the rearend for the last piece I worry about, who knows with my luck I may trip over a good rearend at some point. If so I burn that bridge when I come to it. 

For now, I am going to focus back in on either getting the glass out, rear bumper and gas tank dropped and getting it media blasted ~OR~ get started on the 455 build. 

Who knows :willy:


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## Instg8ter (Sep 28, 2010)

soon to be your 2/3's of the garage....


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