The rear is out of a 99 Z28. 3.42 posi/disc. I assumed I had to change my proportioning valve to work with disc breaks, but I checked my friends 89 IROC with disc and it looks like he has the same valve. Two lines running out of the bottom and none out of the front. Would a 4th gen rear have any difference? I'll install an adjustable one a little later in the summer, but right now we dont have the tools to do it.

Also, would the master cylinder need to be changed? I did a search through old posts and it said I have the T50 (I think that was the number) as did all post-1990 cars.

Thanks, just tryin' to get everything straight before I do it!

Oh yea, the car is a 91 RS.

[This message has been edited by Chuck! (edited May 15, 2001).]

 

You dont have to change the master cylinder,there the same in the later thirdgens.You will need to change the proportioning valve though.I still have to change mine and I did the swap 6 months ago.It is drivable,you just wont feel the benefits of the 4 wheel disc.I picked up a 92 Z28 propprtrioning valve for a few bucks,just haven't had time to put it on.....

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92RS,POLO GREEN

 

Actually, if you have drum brakes now, you'd be better off to NOT change your proportioning valve. Drum brakes get a larger rear balance. As ineffective as the rear discs are in these cars, the additional pressure should serve you well. I'm seriously considering replacing my prop valve with a drum brake one in my 4 wheel disc T/A to try to balance my brakes out a little better. They're heavier to the front than I would like them to be.

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R.C. Righter
86 Trans Am

 

I have just put a '94 disc rear in a '82 T/A. that had drums and have not changed the valve and all works fine. Although the car had reasonable stopping power with rear drums, it stops even better now with discs and the pedal feels the same. The nose does not dip as much under heavy braking and you can really feel the back discs doing their job. Even the brake lines from the '94 fitted at the old tee piece. The only change required was the e-brake cables from the new rear and that only involve stripping the outer casings to expose approx' 10" of cable.