Chrysler 300M

I own a 1999 300M that has recently started emitting a high pitched noise
from under or behind the dashboard on the driver's side. The noise starts a
few minutes after starting the car, and can be stopped by tapping the break
pedal. The noise usually comes back in a few minutes, but sometimes not for
quite a while. If the noise is present when shutting the car off, it
persists for a couple of minutes, then stops. The sound can also be heard
outside the car, but I am having no luck locating the source. The brakes,
and all other systems, are functioning as designed as far as I can tell. The
noise is very annoying. Any help resolving tis issue will be greatly
appreciated. Thanks!

 

Hi it may well be a vacum hose leaking . Some cars use this to deactivate
the cruise control. Check this.

 

Not that it's much comfort, but, according to the following thread on
the 300M ezBoard, several people there have had the problem:
http://p209.ezboard.com/f300menthusiastsclubfrm8.showMessage?topicID=488.topic

It doesn't appear to have been more than an annoyance for anyone. One
person said it was traced to a brake booster problem, and the noise went
away when the booster was replaced. Strangely, on my '99 Concorde
(essentially same as 300M), I have a noise that behaves the opposite:
The noise is not present until I apply the brakes (not rotor or pad
related since it will do it with the car sitting still and the engine
running). The noise will continue with the brakes applied for a second
or two after turning the ignition off, which tells me it is vacuum
related.

I have a feeling both of our problems would be resolved by replacing the
brake booster. If the source of your noise is the same as mine, the
noise will be louder with the hood open than when sitting in the cabin.
It does appear to be coming from the general area of the booster, but
because of the super-high pitch, is hard to localize further than that.

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")

 

I knew a husband-and-wife couple from Arizona who used to drive their
his-'n'-hers '75 Dart and Valiant around the country to Slant-6 Club shows
every spring and summer. The Dart had a musical brake booster: Apply just
the right amount of pedal and you could practically make the booster
whistle Dixie...

-Stern

 

I have (or had) a similar problem with the booster in my '84 Voyager. A former
student (1985ish) who is a journeyman CC tech and who also teaches automotive
(Vo-Tech) training at one of our local high schools and who does CC work at his
home (He has an incredible line up of customers who keep hassling him for his
time) told me what the "problem" was caused by... Anyways, he told me it has to do
with the "valving" in the booster. I looked into the CC service manual (FSM) and
it is rather skimpish on the booster details. However...

They eventually start malfunctioning even though the booster more-or-less works.
The noises are due to the malfunctioning valving.

I was all set to get a replacement since I was going to strip the interior and
replace the '84s interior with a "mint" interior from an '85 (or was it an '86??).
Easy to do when you are replacing the lower front panel.

Now I notice the hiss is gone! No matter. I will STILL replace the booster as they
do NOT heal themselves. intermittent noise now means future trouble. Intermittent
problems are a PITA to diagnose etc. Fortunately for me I understand what the
problem is and how to solve it. I will save potential booster trouble by taking
care of the intermittent trouble now and replace it with CONTINUOUS quiet. A
relatively cheap fix. Guaranteed by replacing the booster. They don't heal
themselves like a broken limb. Been there, done that.

Ken
Winnipeg, Canada

 

Thanks for the link to the 300M group. Like many people posting messages
there, I took the car to the local Chrysler five star service department.
The requirements to become a five star dealership must be loose. The service
manager had poor listening skills, and kept insisting I authorize a brake
job. (I had to tell him three times that I just had the brakes inspected).
Anyway, I set up an appointment to let them diagnose my problem. The wife
took the car in, and they decided the noise was coming from the brake light
switch. So they adjusted the switch and thought they had fixed the problem.
Well, the noise persists, and I had to readjust the brake light switch in
order that the brake lights would not be lit 100% of the time. After taking
the car back and complaining, the mechanic now wants to change out the brake
booster at a cost of $450. I'm taking the car to an independant garage with
a steller reputation Tuesday. Thanks again!

 

Heh heh! Like working on rotors and pads will have some affect on a
high pitch noise that is present with the car sitting still. Scary,
ain't it! (I mean the dealer, not the brakes).

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")