Brakes locked up on me yesterday. not just one butt all brakes. Help

copying this from another thread i started.

Its a 1993 2wd XJ, 4.0L, AX15, and 8.25 rear. i started this thread on Jeepforum.com yesterday with little luck. just going to copy/paste here.

post #1:
I was driving to get the emissions check so i can change the title and get new tabs. On the way there it seemed like the brake pedal was getting stiffer and it slowed down faster than it should in neutral. by the time i leave the testing place and hit the freeway in 4th its having a hard time speeding up. when i let of the gas in neutral again it slow alot faster. This continues to get worse to a point where i drove the 2-3 miles back to work in second gear at 25mph fighting the brakes the whole way. if i tryed to go faster still in 2nd i would start smoking the clutch. Does this sound like somthing broke in the drum it self or the matser cylinder/boster part of the braking system?
Post #2:
well this all happened while i tryed to do the title/emissions crap over lunch break, so i did as much as i could with out getting really dirty. i wasn't able to jack it up to see what wheel didn't spin, but it like more noise was coming from the back end. I think i have encountered nearly all the problems that can happen to a XJ, but this is new. If the brake pedal went to the floor i'd know what to do, but with it getting rock hard and the brakes locking up like that is just weird with out a large bang of some sort.
Post #3
Well i took the rear wheels off and the drums came off easy. the only thing out of place was the adjuster plate on the driver side brake wasn't touching the star wheel and had very little tension on it to hold it up. the wheel cyliners seemed like the where getting stuck possably. Like i said before this happened at lunch and after work i took it around the block and it drove fine. I even tryed to get it to lock up again by slaming the brakes several times. So i just adjusted the rear brakes to a really lose spot and put it back together and drove home and to work today. it still baffles me as to what happened or if it'll happen again. this weekend i'm going to rebuild the rear brakes with new wheel cylinders, hardware, and shoes and see if that'll cure it.
Post #4
when i had the drums off i had my sister press the brakes and the pistons moved in and out on both sides of the wheel cylinder. it didn't look like it was moving perfect but they moved out when pressed and back in when let off.

Would the brake pedal get rock hard if it was a cloged? i would think that the single brake would just be locked instead of having the brake pedal stay hard. hmmm

I am almost leaning toward the MC being jacked.

If the problem is effecting all four brakes then it has to be something that could effect all four--MC would be the most likely culprit, possible fluid contamination should also be considered.

bad check valve in the master cyl would be my guess. Could ck it by breaking loose lines at m/cyl and seeing if it frees up. Plunger in M/cyl could also be sticking and not letting it come back far enough.

From experience, I know that having the rear drums out of adjustment can make them lock up. My adjuster lever that is supposed to turn the "star wheel" on one side also does not touch the wheel. Obviously it was made too long or is the wrong part. I think there were two sizes of rear brakes, so maybe this is for the other size.

Adjust the drums up snugly and then back them off a touch so that you can turn the wheels with only the slightest of rubbing. You may as well try boushing out your fluid. Let me know if you want the easiest way to flush the system, but I have posted it enough times that I will spare the regulars unless you request this.

Sounds like contamination in the lines, water that has boiled, possibly an air bubble as a result. You folks up in the Northwest are having high temps, possibly contributing to overheating or boiling issues. I had a similar event last summer. Ungodly hot day, had a six month old rebuilt caliper seize, but I found it because the car was pulling badly. The right side must have stuck on, then overheated, boiling the fluid, leaving the left side working, pulling to the left. Brake pedal was oddly stiff. Let it cool, thankfully traffic was slow to next exit on Interstate. Got off, crept home, pulled right wheel- I could smell the pads cooking- and the rotor was slightly blued. I had replaced everything six months earlier, and had to do it again. So far, so good....
If it happens again, let your nose help you find the wheel involved, and bleed it as soon as possible, looking for any possible air.