brakes pull themselves in

[russfixr]

Yesterday while hauling a flat bed with a truck on it, I heard a single "pop" and the truck started bogging down. I pulled off to the side of the road, checked fluids and for anything out of the ordinary and found nothing. Got back in the truck and noticed that the brake pedal was not completely up. Held it up with my foot and as I accelerated, it actually pulled down against me. It got worse as I got closer to my destination. I had to leave the truck there and I haven't been back for a closer look. I replaced the hydraboost and master cylinder approximately 4 months ago.

I'm guessing a valve let loose in the rebuilt hydraboost, but I don't know the exact workings of the system. Hast anybody had experience with this type of problem. I read a lot of threads about no brakes, but nothing about self-braking trucks!

Thanks,
russfixr

[russfixr]

In case anybody else ever has this problem. Brakes pulling themselves in is a hydroboost problem. The "pop" I heard while driving must have been a seal letting loose. I replaced and bled the hydroboost and the brakes are back to normal.

Russfixr

[arveetek]

Thanks for the update. That's good to know.

My dad had a weird problem with his '83 6.2L diesel truck that was similar. From time to time, with no rhyme or reason, the brake pedal would suddenly start depressing on its own and slowly apply the brakes. Dad soon figured out that simply shutting the engine off and then restarting it would reset the pedal. It didn't happen all the time, but frequently enough that he got good at popping the gearshift into neutral, turning the key off, back on, restarting the engine, and dropping the gearshift back into drive, all without losing much speed.

Obviously he had similar problems with the hydroboost system.

Funny thing is, after coming down a steep hill into Kingman, AZ, he overheated the brakes, and they never acted up again? I guess a seal must have got hot and popped into place for good.

Casey