I have put a 10 bolt p-trac W/ disc brakes in my 82 z. Will my original master cylinder work? Thanks!:hail:

 

maybe im not asking my question correctly. I believe what I should ask is will my original proportioning valve work? I have the car I got the rear out of. {85 Trans Am}

 

Your original proportioning valve will not work with a disc rear. Disc brakes run a much higher line pressure than drum; the proportioning valve will need to be adjusted accordingly.

 

thanks for taking the time to answer my post. We are going to crank it tonight! New motor,trans & 373 P-tac........i've waited 30 years for this.I hope my mechanic knows how to adjust pro-valve or I might need to ask........ Thanks Again!

 

Now I guess I'm the one that wasn't entirely clear...

Factory proportioning valves are not adjustable, you will need to use the valve from the car that the disc rear came out of or buy an aftermarket adjustable valve. I know that Wilwood makes an adjustable valve, but there are probably others as well. I would just use the valve from the car that rear came out of. Good luck!

 

One thing to note, is that the 82-83 master cylinder and prop valve used SAE double-flare lines and fittings, while the 84-up used metric bubble-flared ones. The line size stayed the same, just the fittings and flares are different.

 

Pete's right... you'll have to either get a prop valve from an 82-83 rear disc, or reflare the lines.

 

thanks again to everyone..........She's alive!!!!

 

If the only difference between proportioning rear drums and rear disks is the increase in spring pressure, therefore brake line pressure, need for disks, can't you just swap the spring assembly from a stock disk/disk valve into a stock disk/drum valve and not have to go through all of the extra work to swap the whole block?

 

sounds like a good question to me. We had hell sat night and yesterday trying to get mine going. I guess I was wrong about the year model of the donor trans am. We rebuilt the calipers and after a broke bleeder screw repair {5 hours}we got the brakes to bleed witout changing anything.I have brakes......not saying great brakes but they work. when I mash the pedal I can hear a "air" sound. My car does not have exhaust on it so I havent drove it a bunch. But, it does stop.I am going to have to learn how to drive it. With the p trac it wants to go sideways and will light "em up all the way through second.It might be after christmas before I can afford to do the exhaust......thanks for everyones help!!

 

I swapped drum to disc on my '82 Z28 a while back and spent some time experimenting with different master cyls and prop valves.

The best setup I got was an '83 J65 rear disc master and prop valve. Got the master cyl rebuilt from wrenchead.com (years ago) and the prop valve from the Chevy dealer.

I used my local NJ state inspection shop to test the effectiveness of each setup...kept failing the fancy in-ground brake dyno test.

1.) With the '82 drum master and prop valve, it was generating near-zero rear braking force.

2.) Changing to the '83 disc prop valve had no effect.

3.) Changing to the '83 disc master cyl did the trick, generated great braking force, passed easily.

 

back from the dead, will it make a difference if you use a 82 master cylinder either disc or drum option if you are using a adjustable proportioning valve? since drum need more pressure, could I put it on my all disc 89 camaro to get more pressure to the rears since they suck so much ***?