84yotaman

i was driving down the freeway and both of my front brakes locked up not completely but noticeable as soon as i relief the pressure it was fine for like thirty minutes then they just locked up again and i know its not the pistons in the caliper because its both sides doing it im leaning more toward master cylinder or lspv (load sensioning porportioning valve) but where is the lspv located? or does anybody know whats going on.. oh and when they lock up the petal is really stiff...

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fourtrax

lspv is mounted above the rear axle, drivers side, and has a rod (that looks sighlty bent) that runs down to the rear axle. i doubt the lspv is causing your front brakes to lock up. However if you have checked out the front calipers and find they are in good working order then you might look at the one way vacuum "check vlave" that is against the firewall between the engine and the brake booster, as it could be bad. next time it locks up temparlary remove the vacuum line from the brake booster and see if the brakes unlock.

the check valve part number is 44730 in the picture below
http://www.autoconnectioninc.net/DaC...e.php?pID=6517

evileyejones

I once had a "friend" top off what he thought was his powersteering reservoir (in a corolla) with fluid, but it was actually his brake fluid reservoir.

whenever my "friend" would drive for about half an hour to an hour, the brakes would start to grip on their own, and eventually would lock up. relieving pressure by taking off the cap, and letting it cool down remedied it till about 15-30 minutes of driving again.

turned out that brake fluid does not expand that much when heated, whereas most other fluid does. so when the fluid that was not brake fluid, but was in the break system heated up, it acted as iff someone was slowly pushing on the break, till it was all the way engaged.

the remedy was to drain the brakes system, and flush all the metal lines, and replace the non metal lines. (shop estimated $1300, I did it in my garage for about $80, which includes one of those hand pumps, new fluid, and the stuff to flush with, I want to say it was denaturalized alcohol or something like that.)

84yotaman

thanks guys i will check it out i bought a new master cylinder and putting it on today i will let you guys know what happens

uijongbu87

I am having this exact same issue, Let me know what you came up with as a solution. Just started yesterday! very strange!

Shoua

It could be something as simple as the brake lines. They may have swollen too much to the point where the fluid will only go one way and not the other. Happened to me before.

uijongbu87

I noticed that after you let the truck sit for a while and let everything cool down. It runs fine. My pedal is super stiff when they stick too. I am gonna check that check valve and see if it is defective.

uijongbu87

Checked the vacuum check valve and that wasn't broken. Could be my master cylinder.... Don't know what to check really. Going to do some more research and see what I come up with before I start buying anything.

Shoua

Check your brake lines!

If they're old and start swelling, it could be letting fluid go one way fluidly but SLOWLY returning back. That might explain why after letting it sit for a while, it'd be okay. Plus, when you're driving, it's creating heat in the brake fluid which would cause things to expand.

uijongbu87

Ok going with Shouas' advice. Gonig to get a new set of brake lines. Fluid comes out, but that doesn't mean a whole lot about fluid freely flowing back to the MC.
So got a set of extended stainless brake lines.
Also, while I am at it, i bought a brand new MC. This should take care of the issue. Lines will be here wed. I will post what the outcome is.

84yotaman

well i put new master cylinder on it but still doing it i have no idea

uijongbu87

Update, I replaced my brake lines and the master cylinder and don't seem to be having the Problem anymore. Although I do know what the problem was. When I changed out the parts, i put in new brake fluid. My old fluid was mostly water. And being right by the exhaust manifold, the fluid would expand, locking up only that wheel...

justjoe

I just had the same thing happen not more than 1/2 hr ago. I was only 1/2 mile from home so I just opened the bleeder valves on the front brakes (one at a time) while my friend put pressure on the brake pedal. Worked good enough to get me to the house.

I noticed evileyejones comment about putting ATF instead of brake fluid in the resevoir. Guess what, I stuck my finger down in the resevoir and found that the fluid was red. Looks like my mechanic has some "SPLAININ" to do, as Ricky Ricardo used to say. Thanks for that one evil eye.

rokblok

Brakes gaining pressure after driving is almost always fluid contamination/condition. As was stated, bad fluid will heat up, expand and apply pressure to the calipers/wheel cylinders. That's whys its important to change/flush the brake fluid every couple years to keep things working right.

I do mine yearly regardless if it needs it or not. And always use good quality fluid.... I prefer just good old Wagner brand, not parts house brand. No need for synthetics or DOT 100 racing silicone super fluid. Just keep it clean and fresh and you'll be good.