I have been told this in the past but I fail to see how this can happen. The only low pedal situations that I have ever experienced resulted from all of the normal causes, air in the system, leak in the system, failed seals, ill-adjusted items, bad brake hoses, worn components, etc. The only result of a bad booster that I have ever experienced has been a higher braking effort but never a low pedal. So can anyone confirm that this is possible and if so, what makes it possible?
i had one that would stick a little and it was new. had to put a return spring on it and it was fine.
bad booster/vacume would just make it hard pedal. if its a low pedal BUT HOLDS FIRM, then its the return spring as stated or the springs on the shoes arent good. or the shoes arent adjusted far enuff out.
My experience has never found a low pedal to be caused by a booster. Almost everything else in the system can cause a low pedal. When you say low pedal, did you just install a new booster and now the pedal is closer to floor that it used to be, or everything was working fine and now the pedal goes closer to the floor before anything happens?
My 65 buick would act like this: With car running, press pedal and it would stay down. Car not running, pedal would return just like normal. I replaced the booster and everything is fine now. Mechanic freind of mine said there is a plastic valve inside the booster that sticks sometime.
Nothing specific, it's just a general question. I hear this claim occasionally and every time I do, I think to myself "How can that be?". The subject just came up again recently, on a non-hot rod based site, so I figured that with the huge knowledge base that is available on TheHAMB, it would worth asking to see if I could get a definitive answer.
should have replied "go to the site called the H.A.M.B. those dudes will probably know" hope this helps.
I had a torino that had a bad booster. The pedal was low and soft, also you could hear the vaccum leak inside the car. I clamped off the vaccum line and it firmed right up. Replaced the booster and all was like new.
Well there you go! This is the reason for my question. It's obvious that the vast majority of the time, a bad booster causes the pedal require more than normal pressure in order to activate the brakes. But every once in a while someone makes mention of the soft, low pedal that was cured with a new booster. Grumpy, when you replaced your booster, did you leave all of the other brake components intact and replace the booster without having to rebleed the system? The reason I ask is to confirm (or deny) that the booster was the sole cause of the problem, not air in the lines that inadvertantly got fixed at the time of the booster replacement.
The boosters I have seen have all been pretty much the same - and that is there is basically a rod that passes thru everything (technically it's a rod and a reaction disc - but for all intents and purposes it can be considered nearly solid and that's the beauty of the design - "fail safe". Meaning that leak you hear while killing the power assist still allows them to work like manual brakes.
Yeah, that is exactly my understanding of a brake booster. So the question still remains, how can such a simple device cause a low pedal situation..................or can it? I don't doubt grumpy's word but it still doesn't seem possible.
I'm not sure. My previous comment was based on the typical single diaphram vacuum booster. Which I've also had people tell me they can get spongy - like you it's not that I doubt them - but I just don't understand how that could happen. Now if a DIFFERENT tpe booster was employed - maybe an air suspended diaphram - or hydroboost then maybe it's THOSE types of booster that can fail in that manner. I don't know how those work to know if thats a possibility or not, but it might explain the disparity.
also, i was thinking.... low pedal could be caused by the master cylinders internal spring going bad/clogged or dirty cylinder. as in- it does'nt push the rubber cup back up to the piston. make sense?
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