[NAC] fix squealing brakes?

[TEX TERRY, II]

From: "Mark L. Chang" <mchang at ee.washington.edu>
(snip)
peachy, EXCEPT the brakes. They have been squealing and making ugly
noises since after a few months of ownership (new). Dealer replaced
everything three times. I replaced the fronts once, and had everything
checked and cleaned and flushed again a few months ago.
They still squeal. They stop well, they show now uneven wear, and there
is plenty of pad life left. What do I need to do to get this thing to
shut up? It squeals the most at the end of the braking zone, between
10mph to 0mph. It starts quietly, then after a couple months, seems to
come from every corner. I can't stand it anymore. The wife is going to
kill me if I can't figure this one out.
New pads? SOOOFT compound? De-glaze pads? De-glaze rear drum shoes?
(snip)

I have found out, through the years, that the squealing is generated by
metal against metal.  In the case of drum brakes, such as in the rear, the
outside edge of the brake shoe may be riding on the   inside of the drum,
but only when pressure is applied.  This will happen if the shoe is tilted
upon installation, or if there is a misplaced mounting guide on the main
inside housing (possible factory manufacturing defect) that is keeping the
shoe from maintaining it's distance from the drum wall during operation.
In the case of disc brakes, a squeal may be generated from the movement of
the disc pad, back metal part, against the caliper piston lip.  To minimize
this problem, there have been pads manufactured with an insulation ring on
the metal backing, so that the piston is not making contact with the metal
backing of the pad.  There is a sound deadening substance available in
parts stores (usually comes in the box with new pads) that is directed for
application on the metal backing of the pads, where the caliper piston will
be meeting the pad.  If there is any misalignment of the caliper "plane"
with reference to the disc (rotor) "plane", then the pads will have a
tendency to be moved out of position, with reference to the caliper
pistons, so that the sound deadening substance used becomes useless.
Calipers may become misaligned due to incorrect mounting surfaces, missing
sliding bolt shims, incorrect mounting torque.  The only normal squeal that
one should hear from the brake system, is when a metal scraper (purposely
attached to the pads) comes in contact with the rotors.  This is provided
to give the driver notice of pads that have become worn to the point of
needing replacement, before it becomes unsafe to drive.

Tex Terry, II
83 5kt sedan (non-quattro)
Franklin, PA  USA