brakes staying engaged

[kerry92gvr4]

ok so about 2 weeks ago i went to the track and ran my car. after about 2 runs my brakes were locked up( would not disengage) i drove it home cause i was not leaving my car anywhere. the rotors were glowing and smoking. i parked it and a week later took off the rotors and turned them at my school, put new pads on, checked the calipers and they seem fine and then. put it all back together and went for a drive. it seemed good at first but then the same thing happened i could feel them not disengaging. so now i am trying to get some ideas or to see if this has happened to anyone. the brakes are all stock even down to the abs.i am thinking the per-portioning valve let me know thanks

 

[Muskrat]

This was more than 1 caliper? That leads me away from sticking slide pins or pistons.

Try disabling your abs system (pull the fuse). These systems are known to malfunction as they begin to age. It may be causing your issues.

 

[kerry92gvr4]

yeah it was more than one caliper, both front, plus like i said when it happened i took everything apart and turned the rotors and put new pads and i didnt say before but i greased the sliders. why would it do it after i raced at the track but not before. i know its bad but i kinda drive the same around town as i do at the track.

 

[kerry92gvr4]

took out both the abs fuses under the hood and its still doing the same thing

 

[Muskrat]

Is your pedal stuck partially engaged?

I can't think of anything in the hydrolic system that could fail and cause lock up. Were the brakes free before you pulled the abs fuse?

 

[kerry92gvr4]

nope, they are engaged, peddle is hard even with the car running, that why i was thinking the porportioning valve might be stuck holing pressure in the front system

 

[Muskrat]

All the prop value does is reduce rate of pressure increase to the rear at a set point in the pressure curve. In fact in the ABS system the front brake lines don't even run to the prop valve. They go from the MC, to the abs unit, to the front calipers.

 

[kerry92gvr4]

your right , i just looked. thank you. so then could it be the master cylinder? i know there are different ports in the master and that there is on that allows the fluid to flow back into the master. if that is blocked or plugged somehow wouldnt it hold the pressure in system?

 

[kerry92gvr4]

anymore ideas

 

[solidviper89]

Reverse-Toyota brakes?

 

[656of1000]

If you were to open the front bleader valves and release the pressure, would the brakes free up? When you changed the pads, did the pistons push in ok?

I wonder if the brake fluid got too hot when you were racing, and a seal inside the master cylinder ruptured, or the front hoses swelled to the point where fluid is not getting through.

 

[kerry92gvr4]

pistons went back in just fine. i was kinda leaning toward a master cylinder also. have not cracked the bleeders yet, kinda think i am going to get rid of the abs all together and when i am putting the new brake lines and p-valve on just completely flush out the brake fluid and put a dot 4 in and a new master ( or different master) and hopefully that would do it because i don't really see anything else it could be at that point. i mean maybe the booster malfunctioned somehow and is keeping the push rod forward but in turn that would make me have a low peddle right for the fact that i would have to make up the clearance before i felt anything, but the peddle is stiff almost solid.

 

[Dialcaliper]

Judging by the fact the car is still "driveable", the pressure on the front brakes is pretty light, more like dragging brakes.

If it were a bad master with a piston not retracting, the pedal would either be really soft in the initial travel, and/or you would be having problems with a diagonal pair or all four calipers, not just the two fronts.

If the booster was going bad and still applying pressure, you'd see dragging in all four calipers
It could also be the caliper pistons sticking, but its odd that its both at once.

Most likely, I would suggest moisture in the brake lines, and a thorough bleeding might fix it (don't forget to bleed the two ports at the ABS unit as well after doing each diagonal pair, or bleed with the engine running so the fluid in the ABS unit circulates). Does the problem "fix" itself when the car is allowed to cool overnight?

If so, what could be happening is when he water heats up after heavy brake use and is under high pressure, it becomes superheated (still liquid, but above boiling temperature) and expands but can't turn into steam. Since this tends to increase the pressure even more and keep applying the brakes (the front brakes tending to run the hottest), compounding the problem. Since it isn't forming steam, the pedal might still be firm.

 

[gmp]

im going to go out on a limb here.. But have you checked the big hose that go's from the middle of your brake booster,to the back of the intake mani?
That big hose has a small one way valve inside the hose, and if it go's bad you can get the same brake syptoms.I know cause toybreaker helped me with this same problem and pointed out the valve inside the hose. As soon as i put in a replacement my brakes felt brand new and i could stop on a dime...

hope my crude pic helps what im trying to say..
Gary.

 

[kerry92gvr4]

thanks. yeah i am finishing up my abs delete today and have a new master cylinder. if that don't fix my problem i will be changing that next. once again thank everyone for your input

 

[kerry92gvr4]

its fixed. it was the brake booster