brakes apply themselves

[taka21]

so im driving along today after adjusting my brake pedal to aleveate some serious squealing
and the brakes seem to just want to apply themselves after a few min of driving
everything ive read points to the brake booster (mine is from a toyota pickup due to my 1uz engine swap)
anyone had this problem???

 

[destrux]

Yeah, you adjusted your brake pedal too tight. Back the adjustment off a bit. There's a spec for it, you aren't supposed to take all the pedal free-play out.

If you adjust the pedal free-play too tight, the booster will actually apply the brakes by itself.

 

[Poodles]

Brake pedal has nothing to do with brake squeel...

 

[taka21]

Yeah, you adjusted your brake pedal too tight. Back the adjustment off a bit. There's a spec for it, you aren't supposed to take all the pedal free-play out.

If you adjust the pedal free-play too tight, the booster will actually apply the brakes by itself.

wouldnt that make the brakes apply before the car could even move ???

what im talking about is that im driving along and the pedal gets more and more stiff till it starts applying the brakes
the free play is there until its not.(if that makes any sense)

the brakes return to normal after i pull the hose on the booster off and then re connect it

---------- Post added at 09:58 PM ---------- Previous post was at 09:54 PM ----------

Brake pedal has nothing to do with brake squeel...

should have been more clear
not adjusting the pedal itself but the booster itself
if i tighten everything down all the way the car wont move at all which would be what destrux is talking about (i think)

 

[destrux]

Brake pedal has nothing to do with brake squeel...

Yeah, I'd have to agree... if your brakes are squealing adjusting the pedal won't fix that.

Also, you're right. I was thinking of the booster rod adjustment, the pedal adjustment would just make the brakes drag constantly. Your pedal adjustment needs to be re-checked after you adjust the booster though.

If the booster adjustment is too tight the booster will use the car's vacuum power to apply the brakes by itself. Depending on how far out of spec it's adjusted it could require a light pedal press to start acting up, or no pedal press at all. It could also be fine starting out and gradually apply them as you start driving. I had a honda accord that drove me nuts with this problem and I traced it back to a booster rod adjustment nut that came loose somehow.

Check the TSRM for whatever the booster is out of to get the procedure for adjusting it, there's usually a depth spec and a specific procedure. It's not something that's easy to guess at. The supra info might be the same if the booster fit the car.

If the brakes are squealing, look at the pads, rotors, and calipers. Probably something there is either worn out, rusted, or seized. Either that or the pads are cheap ones, which tend to squeal.

 

[jpeek29208]

I've had this problem before and it ended being a bad brake booster. Replaced with a new one and it never happened again.

The way I tested it was cap off brake booster from its vacuum source and your brakes should not apply themselves but you will have a increase in the force required by your foot to brake due to no vacuum assist. If that fixes it all signs point to your brake booster

 

[taka21]

I've had this problem before and it ended being a bad brake booster. Replaced with a new one and it never happened again.

The way I tested it was cap off brake booster from its vacuum source and your brakes should not apply themselves but you will have a increase in the force required by your foot to brake due to no vacuum assist. If that fixes it all signs point to your brake booster

ding ding ding we have a winner lol
i actually did this b4 reading and it did exactly that
it takes far more pressure on the pedal to stop the car but the brakes dont lock up at all

 

[Poodles]

Without the special service tool, setting the rod length on the boost is a bit of a pain...

 

[taka21]

does anyone know of a smaller booster i can use and still be good???

 

[Poodles]

Should be fine once it's adjusted. Unless yours is just bad

 

[taka21]

Should be fine once it's adjusted. Unless yours is just bad

the rod is as short as it can be something is actually wrong with the booster because the vac pressure is causing the brake booster to apply the brakes till they lock regardless of the pedal

 

[Poodles]

I'm assuming it's a used booster?

 

[taka21]

I'm assuming it's a used booster?

yea it was used
weierdest thing about it is when i took the mc off and tugged a little on the rod it came loose not all the way out but like it wasnt connected to the pedal side from inside the booster

 

[Asterix]

This document tells you everything you need to know about brake boosters. The output shaft (master cylinder side) is loose, as in it will pull out part way. The input shaft (pedal side) shouldn't be loose at all. It will pivot but not wiggle in and out. The drawing on page 2 of that document (marked 42) is exactly what our booster looks like, but they're all the same.

I found that the instructions in the TSRM for adjusting the pedal shaft were ok, but really didn't tell you to adjust it loose enough. With the pedal all the way up and the booster free from vacuum, that shaft should have quite a bit of play in it. That adjustment is way more important than the output shaft length. destrux got that right.

Your control valve could be sticking slightly. The only solution is to get another booster. Rock Auto has rebuilt ones, though I have doubts they work right, unlike a factory one. The only available factory ones are used at this point.

 

[taka21]

This document tells you everything you need to know about brake boosters. The output shaft (master cylinder side) is loose, as in it will pull out part way. The input shaft (pedal side) shouldn't be loose at all. It will pivot but not wiggle in and out. The drawing on page 2 of that document (marked 42) is exactly what our booster looks like, but they're all the same.

I found that the instructions in the TSRM for adjusting the pedal shaft were ok, but really didn't tell you to adjust it loose enough. With the pedal all the way up and the booster free from vacuum, that shaft should have quite a bit of play in it. That adjustment is way more important than the output shaft length. destrux got that right.

Your control valve could be sticking slightly. The only solution is to get another booster. Rock Auto has rebuilt ones, though I have doubts they work right, unlike a factory one. The only available factory ones are used at this point.

wow that is really usefull
after skimming through that im lookin at the check valve being the culprit (still reading though)

 

[taka21]

yea so i tested the booster and its the culprit time for a new one. the rod actually starts coming out on its own when the engine is on( verified with the mc off) thanks for all your help and input eveyone

 

[taka21]

ok so i changed out the booster and the rod lengh to the master cylinder is as short as it can be and the pedal adjustment is also as short as it can be and it still seems like its too long
cause when i tighten down the booster all the way it pushes the rod out buy a bout a cm and it applys the brakes.
right now i just have the booster backed off enough to not apply the brakes but now the pedal is soft but applys the brakes hard
im really confused