Rebuilt z32 brakes sticking

[Jtuned_andy]

Hey guys, I have a bit of a problem with my 5-lug z32 swap here.

I bought a used z32 setup and installed everything fine. Initially I only rebuilt the fronts because they looked dirty and the rears were left alone. Everything drove fine...

Fast forward untill recently, I have only put a few dozen miles on the car in the past 2 years. The rear brakes locked up on my way home from the shop and I had to literally drag the ass end of the car into my driveway. I proceeded to rebuild the rear calipers because they were found to be sticking, not seized however. I inspected every piston carefully for rust or other possible anomalies, also looked inside each brake piston cup for debris. Cleaned fluid passages with brake clean and compressed air.

The sticking problem continues, after driving the car for about 10 mins with normal breaking the pedal becomes solid and the rear pads have a death grip on the rotor, both sides. If I crack the bleeder screw the pads will loosen and I can drive again for only a short time.

help me please lol

Brake setup

Automatic s13 brake booster
OEM Nabco 17/16 z32 master cylinder
Agency power front & rear brake lines
Aluminum 30mm z32 fronts
z32 rears
Generic pads and slotted rotors.

[ceniack]

possible issue with your master cylider not letting the fluid flow back into it. not sure what type of valves if any there are in there.

[Jtuned_andy]

Yea, in the back of my head that problem is on my list.

However, this same thing happened to me at the end of last summer right before the car was parked again. I made it roughly 10 miles and the rear brakes gradually locked up with the original s13 master cylinder. That's why I haven't gone and pulled the z32 mc out for another one.

I want to mention that if the car sits for 20-30 mins the brakes fully release and I can rotate the wheels again.

My only option left is to drain the system and blow air through each line or check the fluid distribution blocks at the rear and hope there is gunk in the line. But its so hot here and I want whatever I do to work and not have to chase gremlins around :(

[Jtuned_andy]

I've fixed my issue and I suppose for archival purposes i'll let everyone know what the problem was.

So everything turned out to be the brake booster, which I believe specifically was a S13 automatic dual diaphragm unit. I swapped in a manual S13 non-abs booster and the brake lock disappeared. In theory I think that the brake booster adjustment rod to brake pedal was out of alignment and causing the brakes to drag after heating up or something but even after trying to adjust the rod a bit I still had the problem so :wtf:. Instead of fucking with it for very long I just replaced it and it worked.