Rearend Swap to GM 12-Bolt

[rccktmn2]

12 bolt

I think you can bolt that into your g-body. I've got a 68 chevelle 12 bolt under my 84 cutlass. You need a different set of upper control arms which is available from umiperformance.com. Even though the axle tubes are different lengths the center section is the same, you can use this rearend but you would have to go to a different offset on your rims for it to work without your tires sticking out of the wheel wells.

 

[BENCHSEATRACIN]

Chevelle 12 bolt

Not sure if this is much help...but...this may let you know what not to do as well.I have a 70 Chevelle 12 bolt I had narrowed to fit my 86 Monte Carlo.
The G body is 58 inches from axel flange to axel flange.I thought I'd do my self a favor and shorten the rear to be 1 inch narrower on each side than my G body 58...it's 56 inches now from axel to axel.I notched the frame rails,and made them about as narrow as I thought would be safe..it's narrow,maybe 3/4 of an inch.I had already bought a set of 15X8 Bogarts rims with a 4.5" backspacing.My rear tires are the Hoosier Quick Time Pros,11.5x29's (10" tread).I did a trial fit on my car with the stock G body 7.5" rear.To get them on I used a 1/4 wheelspacer and they still rubbed the frame & wheel houses.So I thought,well I'm going to mini tub it & notch the frame rails...so I'll make it narrower than a G body rear so my tires clear the quaters real nice.Now keep this in mind,this is my first G body & had no bodies car to copy from,and pics from the net only help give you ideas,so I more or less I was winging the whole thing.After giving my buddy the measurements I wanted my rear to be I started cutting away.I then realized the rear frame rails aren't very wide to begin with,and that maybe my rear should have been left the stock 58" axel width after all.Now a 3.5" back space rim might fit better than my 4.5" rim,but too late,I spent the big $$$ on these sexy rims & hoped they'd still work.Well yesterday I did a mock up assembly,and my combo is just barely working out.On the passenger side I have about and inch of clearance between the frame rail and the tire,the drivers side is closer,more like a half inch.This will work for going straight at the track,but I have a feeling around turns my drivers tire may rub the frame some..I'll live with it.The only thing left to do would be heat the frame & smash it with a sledge hammer,or buy 3.5" back spacing rims.I'll see how it goes after I start driving it again.I'm also still using my 1/4" wheel spacers to give me this clearance.So I guess what I'm trying to say is,if you narrow your rear shorter than stock,only go maybe a 1/2" on each side not a full inch like I did,or better yet stay at the stock 58" axel to axel width.The reason I went so narrow to begin with,was to keep the tires away from the quater panel lips...almost ruined the whole deal by going too narrow on the rear.I hadn't read anywhere that anybody was narrowing rears shorter than stock..this was my own brain fart..LOL! As they say,live & learn.My tires fit under the body nice,I could lower this car down till the tires meet the quaters & still not rub...which I'll probably do.Right now it has about 3" clearance between the top (4x4 version...LOL) of the tires & the top of the quater lips.I'd like it to sit lower...now I have to figure out how to lower it.I have my stock Monte springs on it.One other tid bit of info...I didn't have to relocate my spring perches.My springs lined up perfect,so I'm leaving them in the stock A body location.(in front of the axel tube,not on top like a G body.).One more piece of safety info..remove the gas tank,or place a piece of steel between the frame & gas tank...it only takes one slip on the drivers side frame rail,and you hit the tank with a red hot mig welder!As you'll see,we opted for the gas tank in-car version.I used the stock upper & lower control arms for the mock up,but I have Iceman adjustable uppers & UMI boxed lowers.

Here's some pics if you'd like to see my near disaster..LOL!
and a link to my photo gallery too..
http://www.benchseatracin.smugmug.com/g ... YwX8#P-1-9

 

[bowtie81]

ive got a 12 bolt out of a 66 chevelle that went right in, all i had to do was change the back spacing on my rims, and i found a guy on ebay that makes control arms for g-bodys for a 12 bolt swap

 

[kornball426]

ive got a 12 bolt out of a 66 chevelle that went right in, all i had to do was change the back spacing on my rims, and i found a guy on ebay that makes control arms for g-bodys for a 12 bolt swap

You wouldn't happen to have a link to where I could get a set of those do you? Or know where I could find some...

I want to eventually put a 425/455 and turbo 400 or a 4 speed manual in my regal... But since I've got a peg legging 7.5 inch with some ridiculous highway gear in it I'm going to do a rear swap first. It seems 12 bolts are easier and cheaper to come by than the 8.5 inch posi 10 bolt. (And stronger?)

 

[shotgun]

I run a stock width 68 Chevelle 12 bolt in the Cutlass.

The tires are 30x9 Radial slick and the rims are 15x10 with a 6.5 offset and fit the stock wheelwell.

Any adjustible upper arm should work as long as one end a sperical or a heim joint.

Better yet, put a TRZ sperical joint in the rears ears along with a adjustible arms and you will have a smooth/no bind rear suspension.

 

[kornball426]

That would be nice since it's gonna be a daily driver I don't want to have a rough ride or have to replace hiems and stuff on a regular basis from wearing them out with binding.

Are rims with that offset more expensive you think? Because one of the reasons I was thinking of doing the 12 bolt is because you see them all the time and thus it's a cheaper solution. Of course I was going to upgrade my control arms anyway so that's not a problem really, other than I was going to go with the ones that have bushings on both ends. And I think the adjustable are more expensive... And if I have to get special rims it might just end up being the same as tracking down a good 10 bolt. I've seen a few for about 500 bucks complete... I see a lot of 12's for about 250-300... So I dunno.

 

[outsider_27]

Re: rears

rosholt, in the corner with ND and Minnesota

You're both pretty close to me in Aberdeen. Who woulda thought.

 

[BENCHSEATRACIN]

Aberdeen SD? You happen to know a guy named Jim Tosh out there?
We have a Aberdeen here in MD.About 15 minutes from Bel Air where I live.

 

[outsider_27]

Aberdeen SD? You happen to a guy named Jim Tosh out there?
We have a Aberdden Md here.About 15 minutes from Bel Air where I live.

He used to live on my block when I was a kid, he lives in a trailer court down the street now.

 

[shotgun]

I would use adjustibles up top no matter what.

If you need to save $, box the stock lowers and use poly bushings in them.

Rims cost the same reguardless of the offset, check Welds on Summit racing.

I wanted a certain rim, Bogart RT, and am too cheap to buy new, so it took a while for aused set to come up for sale. Took another year and 1/2 fora matching set of skinnies. I got $1800 worth of rims for $600.

Do you NEED a 12 bolt? How much power?

Nice thing with the 12 is you can grow into it, powerwise.