This is my first post, so if i did something wrong, sorry.
my problem is this. i have an '88 firebird formula ws6 that had rear drums. i then put a wilwood adj. prop. valve in as described in the tech articals on thirdgen.org. adjusted it and it worked great, braked awsome for a disc/drum car. i then installed a rearend from a '91 z28 which had the prb rear disc set up. since then it hasn't braked nearly as well, even with full pressure going to the rears. the brakes have been bled several times. when the cars in the air and in drive you need full pedle effort just to stop the wheels from turning! could it be the master cylinder. i've read that disc/drum cars have 15/16" pistons and disc/disc cars have 1" pistons. whats the reason for this and do i need to change it. could it have to do with the parking brake. i use it every day, but it also doesn't gab nearly as well as the drum e-brake did. any and all help is welcome, thanx.

 

I would get the disc/disc master cylinder and prop. valve also the parking brake has to be adjusted correctly because it adjusts the air gap on the brakes if those brakes are like the early 3 gen rear brakes. The newer ones have a drum brake just for the e-brake.

 

I agree, the rear disk might require more binding % than the drums.

You would also be surprised of how much binding forces a drum setup can put out. The only draw back to drums, is the fact they can't dissipate heat as well as disk.

I've seen vintage 60's Vettes with kick *** vented drums that can challenge many of today's high performance disks.

Ron

 

You will need to use the 15/16" Master cylinder.

You will need to use the combination valve GM part#14089496.

I will suggest replacing the master cylinder first.

The parking brake adjustment on the '89-'92 rear disc brakes has nothing to do with the normal brake operation. They are completly different from the pre'89 rear disc brakes.

Thanx,ANDYZ28

 

thanx