Prodigious

The other day when I was driving my car home from work, my brake pedal suddenly went really soft and almost completely quit working, I had to push the pedal all the way to the floor to get any kind of stopping power, and even then it felt like only my back brakes were working. Pumping the pedal didn't do anything at all to rebuild pressure. I checked everything the next day, brake fluid was full, there were no leaks or anything. Pedal was still soft and brakes still only worked when the pedal went all the way to the floor. But the weirdest part is that about five hours after I checked everything, I went outside again to check my brakes, and the pedal was firm and they worked just like they always had. It was like nothing even happened. What could the problem be?

I don't want to ignore it since they work now because I feel like I can't trust them. I'm worried that they'll suddenly go out again.

antares57

iTrader: (8)

Possibly the brake booster. Check this out.

https://www.thirdgen.org/forums/brak...edal-when.html

Prodigious

Thanks for the reply, I've already ordered a new master cylinder, and if that doesn't fix the issue then I'll change the booster. If neither of those fix it, then I'm totally stumped. Because as of right now, my brakes work fine, but the pedal is still really soft and goes down too far, which it didn't do before they randomly went out.

I would think that a bad booster would cause a hard pedal, so I think it's interesting that the OP of that topic fixed his soft pedal by replacing the booster.

//<86TA>\\

iTrader: (14)

A bad booster can cause a soft or hard pedal, depends on which side failed. Just replaced one on my old blazer and it was a soft pedal failure and it was the booster

Prodigious

Okay, that makes sense. Once my new master cylinder gets here, I'll change that first, and if the problem comes back, then I'll change the booster. Thanks.

86IROC112

Did you get this resolved? How do you check the booster? I have the same problem. Every now and then my pedal would go soft but would firm up again after a little pumping but the other day it failed and will not firm up again. Going to start with the flexible lines then go from there.


Would like to test the boost if possible..

Prodigious

Yeah, once I changed the master cylinder the problem never came back. So far at least, it's been a while so I'm pretty confident it fixed the issue.

You can check the booster by pulling off its check valve and blowing through it, air should come through one side and not the other. Or you can start the engine, let the car run for about 30 seconds, then hold he brake pedal, then turn the car off. The pedal should not move and if it does, your booster is leaking it's vacuum out. Or you can start the engine, let it run for about 30 seconds, and turn it off. The pump the brake pedal after turning the engine off. Each pump should get harder and the pedal should stop higher.

There are lots of ways to test the booster, but try those first and see if it passes them.