🚀 go-pugleaf

Some time ago, I wrote to this newsgroup concerning a (presumed) brake
squeak in my car.  The essential portion of the original posting follows:

>I have what I think is a rather unique brake noise to deal with.  Everytime
>the speed of my car (an '84 Plymouth Horizon) drops down to around 5mph or
>less, I get a fairly quiet high-pitched squeaking sound from the left front
>wheel, sounding pretty much like air leaking slowly from a balloon.  What's
>interesting is that the noise is exactly the same whether or not the brakes
>are being applied at the time.    
     
I got a fairly large number of replies, some of them suggesting causes that
I would not have thought to check.  Following is a summary of replies,
interspersed with descriptions of how I tried to check the various suggested
causes, posted in hopes that it may help others with similar problems.

***
>Are you sure that the problem is really in the brakes ?  From you're 
>description of the problem, I really don't think it's in the brakes.  If it
>were the noise would change as the brakes were applied. ( stress is placed
>on the components when the brakes are applied which would, at least,   
>change the pitch of the squeal).  Since stress is also applied to the wheel
>bearing during braking, it could also be eliminated as a possible cause.
>I assume you've already checked the obvious things ( tire to fender well
>contact, wheel to suspension contact, etc.). Front-Wheel drive cars are
>notorious for developing weird sounds and disguising them as something else
>(last winter my Citation was exhibiting all the classic symptoms of a warped
>front brake disk.  After changing the disks and pads, no small feat in the
>middle of a Western New York winter, the problem persisted.  It was finally
>traced to the torque-strut (engine mount) it seams the strut was allowing
>the entire engine/transaxle to oscillate during braking) Getting back to
>your problem (sorry for the tangent) I would check the half-shafts
>and engine mounts first for any abnormal play, then I would check anything 
>and everything in the front of the car for someting loose.  If this dosen't
>help, identify all areas which move, or could move, in the left-front of the
>car.  Spray ONE of the areas you've identified with WD-40, let it soak in
>for a while, then take the car out and determine if the problem persists, if
>it does, try another spot.  If you go all the way through this circus and
>the problem still exists take it into the Dealer (yea, I know, I hate going
>to a Dealer's ripoff er um repair shop too, but).  As for my feelings, I 
>would suspect the CV joint ( ugg, I hope, for your sake, that I'm wrong).
>
>					Leo Stearns
>					CCI Rochester,NY
***
   I put the front of the car up on jack stands and ran it in gear at idle
   for a short time to localize the sound.  This confirmed both that the
   sound originated from the hub/brake caliper area, and that there appeared
   to be nothing with abnormal play in the drive train and suspension.  I tried
   the WD-40 trick on everything that looked likely, but it had no effect on the
   sound.  Visual inpection, etc. of the CV joints seems to indicate that they
   were not related to the problem.
***
>I have a squeak on my Honda Accord (which I loath) which my tire & brake shop
>tells me is due to a drum shoe return spring that was replaced backwards (ie
>the hook faces out rather than in, or vice versa) at the last service.  Now,
>I'm not sure what the analogue would be for a disc brake, but you might look
>carefully on the hub, backing plate, rotor outside edge, and other unlikely
>places for tell-tale scoring from something dragging.
***
   This seemed a like a good explanation of what I heard, but examination of
   disk gave no evidence of anything abnormal making contact.
***
>Check the left front wheel bearings immediately.
***
   Difficult to do, due to the fact that they are sealed 'permanently lubed'
   units.  Didn't seem too likely as a cause, though, since none of the usual
   symptoms of a failed bearing were present.  Hadn't thought of it, though.
***
>Are you sure that it is brake noise?  Could it be wind whistling noise
>from the grill or front of the car?  Put a blanket or sheet over the
>front of your car, drive it and see if the noise is still there.
>I have had some very stubborn wind whistles which have driven me crazy
>to find.  It's not like you can walk around looking for it while you
>drive.    
>            Bill Landsborough
***
   Ruled this out by producing the noise with the car on jack stands.
***

Thanks to all of you who wrote to me or the net with suggestions - they greatly
aided me in trying to track down the cause.

After trying the jackstand test already described, I checked with a factory
shop manual and with the only competant dealer mechanic I've encountered.
The former suggested that for noises of theis general type, you should
disassemble the caliper, clean and gease the guide rails for the disc pads,
and re-glue the noise-suppression gaskets between the pads and the caliper.
My friend at the dealership said that the noise I described didn't sound like
any of the usual types of squeak, so that was probably as good a thing to try
as any.

To make a long story short, I did as the shop manual had recommended (not a
bad job), checking for signs of the cause as I did so.  Nothing appeared to be
amiss, with both the disks and pads appearing like new.  I then re-assembled
the brakes and test drove it, and the problem disappeared -- for about five
minutes.  Therefter, it behaved just as before.  Now more than a bit mystified
(not to mention disgusted), I decided to drive the car for a while to see
what would happen before trying anything else.

After about a week's driving, the noise disappeared on it's own.  During that
week, the noise would always appear after the first few minutes of driving.
While I'm still not sure as to the cause, I do have a theory now.

The brake pads in this car appear to be just barely brushing the disk all
the time, even when the brakes are not being applied.  This appears to be
normal on others that I examined.  Apparently, something on one of the pads,
perhaps one of the metal-shaving-like pieces I saw imbedded in the pad material,
was protruding out from the the pad and contacting the disc continually once
the disc got slightly warm.  Once whatevee it was finally wore off, the noise
went away.

Anyway, that's my theory, and you're all welcome to blaze away at it if you
disagree.  We'll probably never know anyway, but if I ever do find out
for certain, I let you all know.

Thanks again for the help, and I hope that this summary helps any of the
rest of you in finding what's causing your version of this apparently very
common complaint.