I converted my 79 to an 83 rear disc. The brakes are locking up on the rear to the point where I can't move the car. I took out the spring in the master cylinder for the rear line. Also took out the spring on the rear side of the proportioning valve. I found this thread https://www.rx7club.com/1st-generation-specific-1979-1985-18/proportioning-valve-question-must-remove-any-doubt-339058/ but it doesn't have an answer. Do I have to take the red piece out of the prop valve or am I better off going with a aftermarket valve from somewhere?

 

Are your brakes releasing, your post is unclear, if you jack the rear up will the wheels turn, from the description it appears the calipers or park brake may be the cause of your problems....

 

Yea, it sounds like the problem is actually at the brakes, siezed caliper, stuck e brake or something, not the hydraulics end of things.

 

Ok good questions. Made me realize that I forgot some details. The pressure gradually builds. I could drive for 10 minutes on the car fine but after it gets warmed up the back locks up. The last time it was really bad I had to release pressure from the valve on the master cylinder to get home. At first i thought it was the E brake. After getting it home and loosening the E brake to the point of being able to roll backwards in the driveway i thought it was all good. Then i take the car out the next day and had the issue where i had to release pressure from the master. The only thing that isn't new on the car as far as brakes is the master/prop valve and the hard lines. Everything else was replaced. I would find it hard to believe that both calipers on the rear are a problem.

 

I don't know why you are messing with the pp valve. I swapped a disc rearend into mine and didn't touch it, works fine. If you are that concerned, find the disc pp valve and be done with it. In the mean time, put the one you have back together.

 

Thanks I will def try putting it back together. I took it apart as a suggestion from my uncle a Mazda Master Mechanic who performed the same upgrade on his 79. Granted he did that a few years ago and couldn't remember exactly what to take apart. The only issue i have with getting a disc pp valve is the threads. I hate to have to replace all the hard lines.

 

Try it with the stock pp valve, It should work well enogh, unless there is something quite different with the SA brake system.

 

I agree. If you remove the wrong thing you could trap pressure in the rear brakes and that could be part of your problem. I swapped a disc rear into my 84 GS and left the stock prop/residual pressure valve alone. Didnt have any problem.

 

i agree with Rx7carl and Trochoid. i've swapped a few rears to gain the LSD and discs and never once have i mucked with the proportioning valve. the brakes worked fine. put it back together. if this locking of the brakes was happening before you touched the hydraulics, i would have looked at the calipers, themselves, first.

 

Yea I did the swap on several originally drum rear cars and left their original prop valves with no issues at all. Unless I'm mistaken the only difference brake wise on the SA's is tha the thread pitch on the lines is different, and that the fronts on 79's have those stupid wedge type calipers.

 

I love it when the answer is clear. I will be putting the prop valve and the master cylinder back together and trying that out. Prob gonna be a few days but I will let you all know of the progress when finished.