'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.
"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
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?
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.
"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....
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
Any other opinions?
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...?
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.