1994 Buick Park Avenue excessive brake pedal effort

Hi gregjyoung. Welcome to the forum. Can you elaborate on "firm" and "heavy". I get the impression "firm" is good and "heavy" is bad. Are you thinking the brake pedal is too hard to push? If so, suspect the power booster even though it appears to be working.

I ran into one of these a few years ago on a friend's car. To me there was nothing wrong with the brakes. They felt fine and the car stopped normally. The only reason he insisted there was something wrong was he owned the car since it was new, and he knew what normal felt like, and this wasn't it after his wife went into the ditch to avoid a deer. The pedal did not feel right to him after they got the car back from the body shop.

Had a half hour conversation with a very friendly fellow who works at a booster rebuilding facility and he explained that some GM boosters have two diaphragms and something happens to one of them. They will also develop the same problem if you get a used one from the salvage yard and transport it laying down. A valve will fall out of place if a special insert isn't used to hold that valve in place. Nice design! So, . . . everything you thought you knew about boosters doesn't apply any longer.

caradiodoc

dear caradiodoc,

whrn car is in "park" brake pedal moves easily enough. it does not feel rock hard like a bad booster or when the engine is not running. when braking the pedal travels normally but brakes require a lot of effort to operate causing my right leg to get tired.

letme know if this helps to clarify things.

Greg

Yup. This sounds like the booster problem I mentioned. I know it defies logic, and this doesn't apply to any other brand of car that I'm aware of. The problem with diagnosing it is it will act like a normal booster. When you stop the engine, you will still get about the normal three pedal strokes before the vacuum is used up. If you don't even get one stroke, suspect a leaking vacuum check valve.

I don't know what the relationship is with the second diaphragm, but when something happens to the internal valve, the pedal is harder to push than normal.

caradiodoc

carradiodoc,

just now i wentout to car, started motor. brake pedal felt spongy in 'park'. felt fine in gear yet seems to require some effort to hold brake. does this help to confirm your suspicion of a bad booster?

gregjyoung

Yes. One other GM characteristic you must watch out for is how easy it is to push the pedal almost to the floor. That is normal when you're standing still, but that would equate to the wheels locked up and skidding if the car was moving. Another way to say this is the car will stop normally from highway speed when the brake pedal is only pushed about 1/3 of the way to the floor. Once the car comes to a complete stop, you can then push the pedal a lot further. That's normal for GM vehicles but it causes a lot of mechanics to believe there is still air in the hydraulic system or the rear shoes are out of adjustment. A lot of time is wasted looking for a problem that doesn't exist. Just about every mechanic learns this the hard way, but once they give up trying to get a better pedal and go out and drive it, they realize it is fine. For that reason, concentrate on the pedal effort needed during a test drive, not how far the pedal can be pushed.

caradiodoc

caradiodoc,

I intend to replace brake booster as soon as time, money and help are available. this will probably be a couple of weeks. will try to let you know how it turns out.

Thank you,
gregjyoung

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