How do i change from drum brakes in the rear to discs. Is it easier to just change to whole rearend or what? I have 3.73:1 gears in the rear and would like to keep those.
Matt

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1984 Trans Am
89 GTA interior, 95 seats, Eibach springs, KYB shocks and struts, Hurst shifter, K&N filters, removed cat, Dynomax cat back, Edelbrock Carb

 

i think the mounting plates are differant for disk. do a search and see what you can turn up about this. if it were me i wouldn't worry about it, drums work as good or better than disk on the thirdgens.

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ICON Motorsports
1st & 3rd
MM Black Diamond 538 F&AM

 

Grab an entire rear if you can. Fabrication is needed to put discs on a drum rear.
Drums may work just as well, and may be comparable in weight, but 4 wheel discs are just COOL.

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88 IROC with cobbled together (not by me)drivetrain, 86 (?) TPI unit on an '83 305,CE subframe connectors, Edelbrock strut tower brace, polygraphite bushings all around...it handles like a dream, but man is it hard to push!!

 

I'm in the process of changing out my RS drum brake,non-posi,3.08 geared rear with a disc brake,posi,3.73(originally 3.23) geared rear.
Cheapest way for me to do it was to buy a whole rearend.See 'em at swap meets all the time for $50-$150.I replaced all bearings/seals, rebuilt the calipers and changed gears before the install,but actually got my rear for $50 at a garage sale!I think the back plates are different, so you'd at least have to pull the axles.Don't expect too much of a braking improvement though,mainly did it to get posi/lower gears.

 

I was told that you can setup your propotioning valve to run more toward the rear which would dramaticlly help your braking do to the larger disc in the rear.

 

The bolt pattern on the axle flange is different from disc to drum. Assuming we're talking 10-bolts, and that you would want to put the '89-'92 PBR brake setup on, here's what you do:

1) Get the entire brake setup off a disc rear.
2) Acquire some disc brake axles
3) Take the 10-bolt disc backing plates, and SWAP them left to right. Make certain that you re-orient them correctly (both calipers on the lower, trailing edge of the axle). Make certain the bleeder screw's the highest point on the caliper. The reason for swapping sides is that the disc backing plate pattern is asymmetrical and the original holes will interfere with the new holes you're trying to drill. By swapping sides, you make certain that there is adequate material on all sides of the new holes.
4) Drill holes for the drum mounting flange pattern into the 10-bolt backing plate.
5) Swap the disc brake axles in.
6) Bolt up all disc components.

There you go. Not that hard, is it?

 

What about a brand new aftermarket rear like a Moser 12 bolt or a 9"? How hard would it be to adapt disc, oh let's say a Baer/Alcon setup, to the rear end or is it already setup? Both are pictured at Spohn's site minus the brakes.

 

Are you sure the disc and drum axles are different? Do they have different part numbers?

 

I unbolted the brakes/brackets from a 9 bolt & then welded the disc brackets to my 10 bolt (formerly drum brakes) w/o any problems, axle or alignment issues. The only thing that was different were the sleeved sections of e-brake cables.

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Well, I found that indeed the drum and disc axles have different part numbers (and thus likely a different design).

I wouldn't be surprised if the drum axles worked with disc brakes anyway (like deadbird says).

 

They have different part numbers and I have heard conflicting results as to whether the drum brake axles will work with disc brakes or not.

 

If your going to do the swap. Remember to put a porportianing (spelling) valve into your car. My car doesnt have it yet and my back disk brakes are extremly weak because of it. Like I once drove 10 miles and when I got to the shop. My front brakes were hot. But my back brakes were so cold I could put my wrist onto them! It wasnt really even warm! O_O

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Chris
91 RS 305 TBI
Eternal Rev

I am sad my car is hurt...

 

The conversion from Drum to disc is not a big deal if you have the backing plates for the disc setup. If you don't have the backing plates you don't have a conversion on your hands.

 

Not true. The backing plates for '89-'92 disc brakes on a 10-bolt are still available from GM. Matter of fact, that entire setup is still available new from GM minus one of the emergency brake brackets.