Strange Brake Pedal Noise

I am trying to diagnose a strange problem with the brakes on my 2001 Ford Windstar. When the pedal is depressed, we hear a sound from under the dash board that kind of sounds like something rubber being twisted or stretched, kind of a loud rubbery sqeaking sound. This isn't the pads or shoes. Definitely inside the car. Plus, whatever this is gives the pedal a jerky feel, plus it seems as if it takes more pressure than normal to stop the car. I have the Ford Extended warranty and the dealer has replaced the brake booster three times so far. However, that hasn't made any difference at all. They tried to tell me that it's normal but it didn't do it when we bought the car and only started in the last 18 months or so.

Supposedly, it's the rubber bellows inside the booster making the noise. But, since we're on our third replacement so far, I'm beginning to wonder. What else could be causing this noise? If it is coming from the booster, is there anything else that could be causing the booster to make that noise? Could a bad master cylinder cause the brake booster to make the noise?

It's worse when the weather is warm and when the problem really gets bad, the brake pedal gets hard to press, as if there is a lot of resistance.

Thanks.

I would have been guessing the brake booster all the way. But with your experience it must be something else.

As an experiment ... why not disconnect and plug the vacuum line/hose that feeds the booster. (This would eliminate a vacuum squeal coming from the booster.)

NOW, DON'T DRIVE on the highway rigged up this way because you won't have much braking force. Perhaps a slow cruise around the block ... to see if the noise still exists.

(I expect the dealer doesn't know what he's doing ... and that's one thing you can't correct merely by repetition!)

I would have been guessing the brake booster all the way. But with your experience it must be something else.

As an experiment ... why not disconnect and plug the vacuum line/hose that feeds the booster. (This would eliminate a vacuum squeal coming from the booster.)

NOW, DON'T DRIVE on the highway rigged up this way because you won't have much braking force. Perhaps a slow cruise around the block ... to see if the noise still exists.
Hmmm, not sure I'm brave enough to try that. :wink: Plus, I'm not much of a mechanic.

The sound may very well be coming from the booster. But, could something else be causing the booster to operate out of spec and therefore make the noise? Insufficient vacuum? Bad master cylinder? I found a post on Edmunds in a Lincoln LS forum of all places that sounded an awful lot like my problem. That person said that their problem was fixed by replacing both the booster and the master cylinder.

Like I said, it's covered under the Ford extended warranty for a few more months and whatever happens, the dealer has to do the work. Of course, they say that there is nothing wrong with the master cylinder or vacuum, but I don't know if they've actually taken the time to check those things. I think they've convinced themselves that it's the booster and can't get past that.

Just an update that might be useful to someone else. Went to a different Ford dealer and they've fixed the problem. Turns out it was a bad master cylider causing the booster to make that noise. That was my theory all along, but the dealer I went to first didn't want to listen to me.