breaks lock up

once or twice in the past my f. breaks would not release, there for locking up the front tires.
this morning when i was going to work, the truck shifted down to go up a hill. not to strange, but then it got slower and slower. i had to all most floor it to get it to a safe stopping area. for some reason the breaks started to lock up on me. i didn't apply the breaks at all until i pulled it over. i had to pop the hood and loosen the break line coming from the proportional valve and the master cylinder to release the breaks. after that it worked fine no problems. I replaced the master cylinder just the other day.

Any help on what it might be?

bad calipers? proportioning valve acting up?

If it was the calipers then releasing the pressure from the line before the proportioning valve would still not release the breaks, correct?????
So if that is right then it might be the prop. valve.

You say you replaced the master,did you reverse the lines?

lol, no....................... well hummm, naaa

Well, i believe it is the master cylinder, again.....
It happened again last night when i had to help out my bro, his s-10 is over heating all the time and we can't fig out why. I even pulled the thermostat out thinking it was that. (rabbit trail)
In order to get the breaks to release last night i loosened the out-put to the f. breaks from the master cylinder and it worked. This will be the 2nd one i have put on this truck with in 3 mo. Good thing for life time warranty. The first master cyl. wouldn't work at all, no breaks. Now this one is all breaks, so hopefully the next one will work correctly.

Must be a 84-88 problem. I've been through my original and 3 aftermarket. FINALLY got one that doesn't leak.

Yea, it's an 86. The very first one leaked now i got this problem.
From what I hear now this is a commend issue.
I'm about to go with the Bedrocks breaks system.

make sure you have a gasket between the booster and master. they dont sell them at parts stores...and they sure don't tell you about them. toyota can get them for a few bucks though. i made one out of cork, i didnt want to wait.

That's good to know. I'll prob. make one as well. lol
All tho i did find out that you can still buy a master cyl. rebuild kit.