I found tidbits of info but I need someone to specify some stuff for me.

personally, I know the ford foxbody bumper to bumper, and all the stuff with axles. These F bodys are hard to figure out kinda.

Anyway, heres what I am looking to do.

On my tbird, I am swaping out the crapola 7.5 open diff with a 8.8 with posi and disc brakes from a turbo coupe.

For this camaro, I would like to do the same (with gm stuff of course)

acording to this site, my 85 should have a 7.625 rear end. What gm axle will offer posi and disc brakes? I think I read about a borg g92 axle on here, but that sounds hard to find.

Also, on the fox you have to use a bigger master cyl for disc rears, is that the case on these cars?

The guy I bought the car from has a 2000-something SS, and he just swaped his rear end with a better one, but im guessing 3rd gen and 4th gen are different widths?

New rims are out of question, I like the stock brown ones and how they stay inside the fender with my 255 BFG's

You guys will probably bash me for not searching hard enough, but I just need a solid answer on what to look for/ easiest way to get what i want in a axle.

Thanks

Blain

 

First of all, ignore everything you know about ford axles.

Your 85 will probably have 7-5/8" ring gear but may be a 7-1/2. Other than the ring gear size, nothing else about the diff changed. You'll have 26 spline axles. 28 spline axles didn't start until 1990.

The Borg Warner 9 bolt was only available from 87-89. It's a 7-3/4" ring gear. It is a bit stronger than the 10 bolt but parts are difficult to find. The diff is made in Australia and used a lot on the Holden.

Finding and using a 4th gen diff doesn't increase the diff strength by very much. In 1990, GM started using 28 spline axles but you can convert your diff to 28 spline axles for the same strength. The 4th gen diff is about 2" wider on each side. Some people have had no problem with rims, others go with a different offset to tuck the rims back under the fenders.

Because of the torque arm suspension, there is no other GM diff that can easily swap into a third gen other than from a 4th gen. Your only other options are to buy an aftermarket diff such as a bolt in 12 bolt, 9" or Dana 60. Expect to pay around $2500 for a complete diff.

The best direct bolt in factory diff to give you posi and good disk brakes will be out of a 90-92 third gen. Good luck finding one in good condition. It's common for those who convert to rear disk brakes to also grab the master cylinder and combination valve.

 

Moser makes a very good bolt in 12 bolt rear end for these cars, but it is expensive. Once you have one you won't have to worry about anything breaking in it.

The second best option is the Dana 44. This was offered by GM as an over the counter option on these cars. I saw one for sale on this sight about a week ago for around $1500. This is a pretty strong rear end.

The Borg Warner is next. Not a lot better than the 10 bolt, but still an imporvement. The 4 pinion posi is stronger than anything you can get in the little 10 bolt. There are a few for sale on this sight, including one that I have listed.

Go to the parts for sale page and look around. You will see some disc brake rear ends for sale there.

I know that some people are going to say to get a 9 inch Ford. There are several bolt in 9 inch rear ends that you can get, but it's my opinion that the 9 inch is too much for most of these cars. The Moser 12 bolt is more than enough to handle most street/strip cars. The 12 bolt can get a car well into the 9s without breaking. You put 8.8 rear ends into your FOX cars, so you probably already know that the 8.8 is enough for most street/strip use. The 12 bolt is almost exactly the same as the 8.8 except for the number of splines on the axles and the number of bolts in the ring gear.

 

with both of them.

 

Okay, great info. So, considering the cost of swapping a new axle, can I just posi mine, get moser 28 splines, and somehow convert it to disc? or is the disc option only available on a new axle?

I'm not drag racing/ ripping 900 horsies through this rear end, I just like knowing it can take everyday abuse from my lead foot thats all.

I will keep an eye on here/ craigslist/ junk yards for a 90-92 rear axle. Now, this means all 90-92's will have this axle? or certain base models have it?

also, how much should it be?

I know a rebuilt one is expensive. I wouldnt mind having a rusty one to clean up, but a used one should go for under 500 right?

I could always have the posi rebuilt if its worn out i guess..

-blain

 

Your best bet is to just swap out your current rear for one with disc breaks. I put a 4th gen rear in my car when i broke my old rear end. If your not willing to shell out the money for an aftermarket one getting one from 1990 and above is your safest bet. I got my rear from a 95z with the 11.65 inch PBR brakes complete with 3.42 gears for 350. Usually a 10 bolt form a 90-92 car will be around 200-250 and a 4th gen rear with 11.65 brakes will run you around the 250-350 range from a yard. The LS1 rears came with a torsen diff and bigger 12 inch brakes and will probably be the most pricey of the rears with 28 spline axles. I happen to like my 4th gen rear. My 95z rear is pretty much the same as a 90-92 thirdgen rear with the exception of it being 2 inches wider and probably having less miles than anything you will find from a thirdgen.

Here is a pic of my car after i put in my new rear, Im still running stock 15inch RS wheels with i believe 245s on there. Originally it rubbed the tires going over hard bumps but i rolled the fenders and now i have no problems.

 

The '85 drum brake rear end will have the wrong housing ends to do a disc brake swap. You need a later housing, or a disc brake housing. These have 4 bolts in the brake bracket, where the earlier housings have a large bolt with 2 smaller bolts to hold the brakes on.

 

All '90-'92 axles are 7.625" 28 spline, even the V6/automatic cars. These can use the same rear discs as the '93-'97 V8s, AFAIK. Maybe just '93-'96. Anyway, these are way better than the rear discs on the '82-'84s, even though the earlier housings can be upgraded to 7.625 ring gears and 28 spline.
The best rear discs are the '98-'02 V8

 

The drum flange can be modified to accept disc brakes. There's a how-to on site.

JamesC