does andybody have a ballpark figure on how much it would cost to have a GM 12 bolt rear cut down to size to fit a third gen??? What all has to be done, and more importantly how much will it cost??

Cutting it down isn't hard. You'll need to buy new axles though. You'll also need to find some way to attach the torque arm since there are no factory 12 bolts that use the same suspension mounting hardware as a third gen. Since the housing is cast, I wouldn't recommend welding a mount bracket onto it. By the time you're done modifying or changing your suspension to get it to work, it would be cheaper to just buy an aftermarket bolt in housing with axles.

You might want to look into getting a 9 bolt out of a later year Iroc (87-89 ?). They are the strongest rears that were put into the 3rd gens. I'm in the process of rebuilding mine with a 3 series posi and 3.70 gears. Check out you local junkyards and ebay. I got the 3 series posi and 3.70 gears for under $400 total off of ebay. It should hold up alot better than any F-body 10 bolt.

well i want a 9 inch so then i get the bigger ring and pinion gears to give my car a greater mechanical advantage...do they sell axles in different sizes to fit or do I need custom axles??? I think I can handle the cutting down of the housing, that doesn't look to difficult...is it a project my dad could do since he is a pipe fitter and does a lot of welding, or is it something that has to be professionally done??the suspension I don't think would be too too hard, i would probably just buy some ladder bars and weld some brakets...and make my springs and shocks work accordling..

this may help u...

http://www.bmrfabrication.com/F3-chassis.htm#rearends

OUCH...just over 2 grand for a rearend.....i was thinking maybe 750...there has to be a cheaper way...can't you get a 12 bolt or 9 inch from a junkyard for a couple hundred bucks?

$2000 is for a complete bolt in diff. Everything included although it might not include brakes. You can pick up the housing with axles for less than $1000 then find your own center section with gears, carrier etc. Then figure out what brakes to use.

Finding a junkyard 9" isn't easy since you need to find a donor vehicle with very close to the same width as your car. Then you need to move all the mounting hardware over to the 9". LCA, panhard and shock mounts are easy. You still need to find a way to mount or eliminate the torque arm.

My housing is out of a 1970 F100. I bought some custom 31 spline Strange axles for it. I already had a 31 spline spool with 4.56 gears in a carrier. I used Ford drum brakes. I don't use the torque arm/LCA setup because I installed it with ladder bars.

okay how about this...what if i found a housing for real cheap...bought a full spool, ring, pinion, axles, and anything else I need, would that be a lot cheaper???because mostly what you are paying for is the posi unit....also is there any difference between a 12 bolt, ford 9 inch, and a dana rearend, or are they all pretty close to the same...aslo what do i have to do with my brakes....buy ones to fit that rearend or will my stock ones work?? For my suspension I would probably use ladder bars...can i do this with a lowered car? also i saw somebody rig up a panhard bar in between his ladder bars...is there a bunch of geometry in this or what??

Hey Stephen, or anyone, what do you think would be a best place to order a 12 bolt or a 9" from Calgary,Canada here. I was possibly thinking fasttoys.net, as they are Manitoba based and don't charge duty, but that is bull too as last time I got an LT1 clutch from them, I got charged duty 'cause, they said, it wasn't a stocked unit so it came from the states. I doubt that a 12 bolt they sell they got in stock. So what do you think?

I just got my 383 running, and I want to get either a 12 bolt or a 9" with 4.30 gears, as I am gonna run a T56. Thanks.

P.S. Its for my '88 car. I also have 4th gen wheels and other 4th gen parts (my '94 was written off, got it back for parts), etc. I know some aftermarket axels come in 4th gen width only. Thanks.

I don't know of any Canadian suppliers but I'm sure there are some. Try asking at Mopac. They buy directly from the dealers. You could even get a discount on the shipping if it came in on a regular stock order. I order stuff like that all the time. Make a special order then wait a few weeks or a few months for it to arrive. Hardly ever pay for shipping. Difficult to say with the diff though because it's so heavy.

I talked to Bill already, he said they get no special deals on them at all and they ship it separatley. Said it would be best to order from them direct. I've been doing some checking, and I think it would, in fact, be the best to order direct and take some time to recive it. I'll have to get one very soon.