Master cylinder building pressure

[stinsonj]

For some reason, my master cylinder is building pressure to the point of locking up all brakes. Since all 4 are locking up, it has to be the master cylinder. This happened a couple of weeks ago while towing my jeep to the dmv. When i got home, all 4 brakes were near locked up and smoking. So i did a rebuild on the master cylinder, which was dirty beyond belief (filled with rusty sludge. Its amazing it worked at all in the first place). Went wheeling yesterday, and when I got home, i noticed the brakes were locked up again. So i guess my question is, do you think i just need to buy a brand new master cylinder? Or just take it apart again and clean it some more (I thought i got it pretty damn clean the first time) Also, is there a pressure relief hole inside of the MC that i should pay particular attention to when cleaning?

 

[BrockGrimes]

When it comes to brakes never cheap out. Go ahead and buy a quality MC.
I'd also recommend doing a flush on all the brake lines before installing the new MC.

I built a pressure bleeder like this:
bleeder

When I first got my jeep the brakes didn't work and the MC was dry, rusty, nasty.
So I replaced it and did a full flush of the brake lines.

I just hook a piece of clear tube from the pressure bleeder to the line at the MC
and put a tube on the bleeders, then drop the line in a gallon jug to catch the
being bleed off.
Pump the pressure bleeder a few times and it flushes all the from the MC
end of the tube all the way down to the wheel and into the gallon jug.

 

[IOPort51]

there is a thing called a proportioning valve on the drivers side frame rail, It costs about $75 and requires a good tubing wrench to change it out. this is what I would bet lunch on if it were mine. and Brock is right, flush those lines, bite the bullet and spend the cash.
Dad always said " a car that stops well is worth more than a car that goes fast."

For some reason, my master cylinder is building pressure to the point of locking up all brakes. Since all 4 are locking up, it has to be the master cylinder. This happened a couple of weeks ago while towing my jeep to the dmv. When i got home, all 4 brakes were near locked up and smoking. So i did a rebuild on the master cylinder, which was dirty beyond belief (filled with rusty sludge. Its amazing it worked at all in the first place). Went wheeling yesterday, and when I got home, i noticed the brakes were locked up again. So i guess my question is, do you think i just need to buy a brand new master cylinder? Or just take it apart again and clean it some more (I thought i got it pretty damn clean the first time) Also, is there a pressure relief hole inside of the MC that i should pay particular attention to when cleaning?