Hey everybody, I'm about to my wits end with this issue i've been having with my '85 GT-S.

C/N: Pedal Stiffens while driving and eventually brakes get stuck on.

Back Story: When I bought the car the power brakes were not working, so I changed out the brake booster with a new unit, and unclogged the line going to the booster which fixed the power brakes, however at this time a new issue also started. As I drive the pedal goes from normal to super stiff and eventually it gets to the point where I cant press it and my brakes are stuck on. I changed the master cylinder and bled the brakes multiple times. There is not much pedal drop when bleeding the rears, but the fronts bleed as normal, and I've pulled the hard lines and verified that fluid is making it past the proportioning valve. I can alleviate the issue by opening the hard lines on top of the master cylinder to relieve pressure and restart the process.

I'm clueless why this would start when I changed the booster. Maybe the adjustment for where the pedal attaches to the booster is wrong? Could that cause an issue?

Thanks in advance for any advice.

Have a read of this thread...

http://www.ae86irl.com/forum/showthread.php?51644-Rear-brakes-sticking-issue

Cheers... jondee86

EDIT: For the benefit of anyone who can't view the above thread, the keys points are...

It is essential for proper brake operation, that the brake master is not pre-loaded
in any way. If the master is pre-loaded and not allowed to return all the way when
the brake pedal is released, it cannot fully release the fluid pressure after brake
operation. With each operation of the brakes, the pressure ratchets up (gets higher),
until eventually it can lock the brakes.

The master can be pre-loaded in two ways... either the booster pushrod (between
the booster and master) is too long, or there is no freeplay in the brake pedal. You
have to have about 5mm of movement in the brake pedal before the booster input
pushrod begins to move.

Could this happen if the one way valve in the vacuum pipe was fitted the wrong way around ?

totta crolla wrote:Could this happen if the one way valve in the vacuum pipe
was fitted the wrong way around ?

Not if having the one-way valve around the wrong way, was the only thing wrong
with the brake booster. All that would happen is that there would be no vacuum
assistance. The pedal would be hard, and you would have to press hard to get any
braking, but the brakes would not lock on.

Cheers... jondee86

Thanks for the response fellas. The problem ended up being the rod in the master cylinder side of the booster was adjusted out way too far causing pressure to build but not be relieved. I adjusted it back and the car has been going good for 2 days. Good on ya' Jondee with the right answer. Thanks man.

Pretty much just like this video, but adjusting in instead of out.

http://www.youtube.com/watch?v=GrFEzfDnzqM