1982 Olds Cutlass Supreme Posi Rearend Swap

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Not-quite-so-new-guy
Nov 4, 2017
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Nebraska
Hi Everyone! I've been referring to this site for years, finally signed up!

I am looking to put a stock "junkyard" complete posi/limited slip rearend drum to drum in my car. The car is an 82 olds cutlass supreme brougham. It has the 7.5 rearend, one wheel wonder. I have a thumping 71 olds 350 Rocket pushing over 400hp...spinning 1 wheel all the time. Rearend has handled the abuse flawlessly. My question is what particular rearends will bolt up without any modifications? I'm sure it's been done.
Any 78-87 g body?
Thanks!
 
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81Regal

Royal Smart Person
Apr 5, 2009
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Terril Iowa
Any g body 7.5/7.65 is a direct bolt in. The 8.5 inch rear is a bolt in with a 1" shorter driveshaft.
 
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Ribbedroof

Comic Book Super Hero
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Jan 4, 2009
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One small note, rears before the 1982 model year use 7/16-20 SAE wheel studs, whereas the 82-88s use 12mm x1.50 studs.

I personally do not like mixed studs on a car, which that car over
<-------- there currently has. It's on the list of changes when it gets torn down for rebuild.
 
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MrSony

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Nov 15, 2014
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Yeah, make sure about the studs. Not hard to change em. Keep in mind, there are 2 carriers the 7.5s used. The series 2 and series 3. iirc the series 3 is 3.08 and numerically higher (3.23, 3.73, etc) and series 2 is 2.14, 2.29, 2.41, etc. You could just buy an aftermarket posi setup and refresh the rear end. I'd poke around on craigslist. I've seen a lot of 3.73 monte rears (7.625 rear end) on the net for sale. As said above a GN/442 would drop right in (GNs had 3.42/3.73s, 442s had 3.73, posi was optional on both. The thought of a one wheel peel GN makes me giggle.) with a 1 inch SHORTER driveshaft. The 7.5 d/s are spindly and would probably rip in half from your 350. If it's got 400hp like you say, it's got damn near 500ftlbs.
 
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Oct 14, 2008
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Expect the stock spider gears to eventually explode. Either the 3.42 or 3.73 7 5/8 Monte SS rear is an affordable swap. They have more even sized spider gears which help durability. As said the 8.5 with it's heavier duty 1" shorter is by far the best factory rear. Either get a Ford 9" or make one or the 8.5". Expect to pay $$$. You can pick your desired gear ratio, a Detroit Trutrac or find a 4th Gen F body 7 5/8 posi carrier, good factory gear ratios and a Zexsel Torsen worm gear posi, the same as the Trutrac. The F body rears have 28 spline axles vs your stock spindly 26 spline axles.
 
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Ribbedroof

Comic Book Super Hero
Supporting Member
Jan 4, 2009
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Yeah, make sure about the studs. Not hard to change em.
.

It does take a little digging through the book to find a stud that fits, as I recall, the 12mm stud has a larger hole at the knurl than the 7/16.

Not an insurmountable task, but asking the average chain-store counterman for studs that are not a direct application can be .....trying.

The easy way out is to go the matching rotors....unless you have a '78
 
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Kwik_Cutty88

Royal Smart Person
Nov 22, 2011
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Cars you can grab from to replace the entire housing without modifiation?

Another g body

You can also pull a variety of center section out of junkyard cars.

You can get a gov lock 7.5 (a good way to make your 7.5 weaker), an auburn cone style (not rebuildable), an eaton style, a torsen out of a 4th gen camaro and many more. Anything newer than 1988 will be 28 splines, and yours is currently a 26 so that is something to think about. I ended up snagging a set of stock GN 28 spline axles for cheap on ebay. That allowed me to run the 28 spline 7.5 carrier I got for free. 26 spline posi's can be hard to come by, 28's are usually a little cheaper (used) from what i've seen. You'll also need to consider what gear ratio you want to run so you pick the right series carrier. You can pull a center section from almost any GM vehicle that came with a 7.5 and it will drop right into your housing. Blazers, S10's, Camaro/Firebird, etc.

The G body 8.5 is also an option, but they can be tough to find and pricey. You could also do a Ford 8.8 out of a foxbody mustang with a trick chassis swap kit, or even a g body specific ford 9”
 
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Rocket Powered

Not-quite-so-new-guy
Nov 4, 2017
24
11
3
Nebraska
Yeah, make sure about the studs. Not hard to change em. Keep in mind, there are 2 carriers the 7.5s used. The series 2 and series 3. iirc the series 3 is 3.08 and numerically higher (3.23, 3.73, etc) and series 2 is 2.14, 2.29, 2.41, etc. You could just buy an aftermarket posi setup and refresh the rear end. I'd poke around on craigslist. I've seen a lot of 3.73 monte rears (7.625 rear end) on the net for sale. As said above a GN/442 would drop right in (GNs had 3.42/3.73s, 442s had 3.73, posi was optional on both. The thought of a one wheel peel GN makes me giggle.) with a 1 inch SHORTER driveshaft. The 7.5 d/s are spindly and would probably rip in half from your 350. If it's got 400hp like you say, it's got damn near 500ftlbs.

The monte carlo is the route I was thinking. I've got the engine running the way I want. Now time for a rearend and body/paint. According to desktop dyno it out like 405 hp. I can spin and keep spinning the one tire,lol, at 60mph...
 

MrSony

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Nov 15, 2014
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Des Moines, Iowa
Around where I live there are tons of dirt track racers that use g bodies and shove the old rears (posi or not) on craigslist/facebook and swap in ford 9 inch housings they make themselves. My grandpa used to rac
The monte carlo is the route I was thinking. I've got the engine running the way I want. Now time for a rearend and body/paint. According to desktop dyno it out like 405 hp. I can spin and keep spinning the one tire,lol, at 60mph...
Same. I had a 350 Buick in my car (first engine I built) and that thing, even with 2.41 gears and like 7.8:1 compression, it would light up that tire. Poor 195. I think I had around 270hp and 350+ftlbs.
 
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Rocket Powered

Not-quite-so-new-guy
Nov 4, 2017
24
11
3
Nebraska
Thanks for all the info guys!

What gear ratio should I look For? I have a 15 mile drive to town? Not looking to rev 4000rpms at 60mph. 342s or 373s? I have a built th 350 full manual valvebody 2200stall converter
 
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