newbie here with serious brake problem on 85 sr5,have change master cyclinder,rotors,calipers,wheel cyclinders,power booster everthing but brake lines and proporation valve still cannot find problem.runs great till you hit brakes couple of times then driver side calipers lock up will not release till you undo bleeder screw.then releases pressure start down the road again smell brakes ahd then BAM!LOCKS UP AGAIN.really starting to be a big problem.have no fluid loss and only one side seems to be locking up?please help!thanks

 

This sounds like you have some type of contaminants in the system. Suggest that you have the brake system purged to flush out anything left over. I had a 72 240Z that would lock the rear cylnders when they corroded. A simple clean out with ffine sand paper then a through cleaning worked wonders - replacement did the same thing.

 

when your brakes are working freely clamp off the hose by th top so the fluid won't pass threw.drive ot around then if it works fine after you do that you have a messed up front brake hose. it's collapsed inside and won't let the fluid pass threw properlly. hope that helps you out

 

If you've replaced all of those things and its still locking up, it sound like your fuel line is blicked and acting as a one way hose. Because of the pressure created in your break booster, the fluid is getting through to Activate the calipers, but the calipers are not strong enough to push the break fluid back up! Hope this helps!