SWMBO and the noise I can't hear

'02 300M. ~130K miles.
My wife is telling me, insistently and forcefully, that there is a high-pitched sound that is driving her crazy every time I apply the brakes -- and (often but not always) even when I keep my foot on the brake pedal after the car has stopped. I cannot hear it at all.
Ideas?
Perce
Reply to
Percival P. Cassidy
"Percival P. Cassidy" writes:
Until you said it sometimes continues when stopped, I was all set to tell you about anti-squeak sprays for the rotors. But all I can imagine that could do that when stopped might be a pinhole leak in the brake booster? Try starting the engine, letting it run for a couple of seconds, and shutting it off again. You should be able to wait a while, and when you press the brakes get power assist for a couple of strokes. If not, the booster is leaking. Just a guess...
The other option, of course, is you just need to turn the radio up louder :)
Reply to
Joe Pfeiffer

I was already thinking along those lines before I read your response, as further discussion with my wife showed that the noise isn't dependent on my foot being on the brake pedal but rather just not being on the gas pedal.
Where is the leak likely to be? Just in the hose from the manifold to the booster? Or maybe the rubber has become hard and isn't sealing too well? Or...? It seems from the service manual that the booster isn't so easy to get at; am I right?
Perce
Reply to
Percival P. Cassidy
the PCV valve is way back on the rear of the block if I remember right. I kept hearing a sound like that on my LHS when I let some guys change out my rack and pinion (didn't have room to work on it here at the house at the time). I had to just reattach it because they had forgot to.
Reply to
Rob
"Percival P. Cassidy" writes:
Oh, hang on -- if it isn't dependent on your foot being on the brake then there's no reason to assume it's in the brake system at all. I wonder if it could be in the throttle body? Try hosing the inside of it down with throttle body cleaner (which is likely to be no fun, since the throttle body is 'way in the back where you almost have to take the fascia in front of the windshield off to get at it....
Reply to
Joe Pfeiffer

SWMBO got on my case about it again today and said that some passengers commented on the noise too (also said that the noise stops when she presses down rally hard on the brake pedal with the car stationary), so I got my car-savvy neighbor to come listen. At first he said it sounded like an electronic noise. but then he noticed that the noise continues a while after the engine is switched off [I, later, to my wife: "The noise is still there after the engine is switched off." She: "Yes." I: "You didn't tell me that." She: "No." I: "Arrgh!"].
Then he found that the noise was not there when he disconnected the vacuum line from the brake booster. So we figure it is either, on the one hand, the check valve or its grommet, or, on the other hand, and more likely, unfortunately, a leaking brake booster diaphragm.
So my inclination is to buy a new check valve with grommet first and see if that solves the problem, and only after that, if necessary, buy a replacement brake booster; I've read that that job could take a couple of hours.
Any other opinions?
Perce
Reply to
Percival P. Cassidy
also if you have some carb or throttle body cleaner you can spray a little around those connections while its running and you should be able to tell a difference in the engine RPMs if there is a leak.
Reply to
Rob
Neighbor came over with a stethoscope today (after I had already installed a new check valve and grommet and was about to restart the car) and poked around. The noise was still there but went away when he pushed up on the master cylinder -- and still there after tightening the nuts on the mc-to-booster studs.
I can't find anything in the manual about any kind of seal between the master cylinder and the booster. Is there a gasket or O-ring, or...?
Perce
Reply to
Percival P. Cassidy
To answer my own question: judging by the pictures I've found online, that's a purely mechanical connection; the only seal there is where the rod goes into the booster. So it looks as though the only way to get rid of the noise is to replace the booster.
Perce

Reply to
Percival P. Cassidy

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