[s-cars] Re: Brake Squeal

CyberPoet thecyberpoet at cyberpoet.net
Fri Jan 3 01:23:48 EST 2003

The Physics of brakes and brake squeal:

Everyone on the list should be well acquainted with how brakes work in
general, so I won't cover it the basic theory. Here's what you might
not have known:

Brake Squeal is traditionally induced by the vibration of the pad
backing at an oscillation rate that makes it audible; it is not
normally induced by the pad material-rotor contact (although it may
appear so at first). Thus, the secret to eliminating brake squeal is to
eliminate the excess vibration, either with a backer material (felt
used to be used a lot, but it's not very friendly to the temperature
ranges of modern braking systems under load), or with some form of
lightweight spring designed to keep pressure on the pad (but not enough
to wear it down significantly). Since sintered pads are designed to
drag lightly, they usually have springs, while organic pads are
designed to float and traditionally use some form of backing material
to eliminate the vibration. The vibration can take place between the
backing and the caliper, or in modern cars, is more often caused
between the backing and the mounting system it rides on.

As for brake pad material build-up on rotors, sintered brakes (metallic
pads) function by depositing a layer from the pad onto the rotor and
then making contact between that material in the pad and that material
on the rotor. This is designed to lengthen the rotor life and to
increase the braking friction (since the rotor is a smooth surface);
cleaning the rotor (or resurfacing it) eliminates this layer and thus
decreases the braking force until a miniscule layer is built up again.
Organic pads (kevlar, ceramic, non-metallic and semi-metallic pads)
aren't designed to deposit that same layer, and switching to them after
using sintered pads requires resurfacing or bead-blasting any deposit
layer from sintered pads off the rotor for the organics to work
properly. Failing to do so can easily lead to transference of the
organic material onto the sintered layer on the rotor and then that
material glazing in turn (since sintered pads normally operate about
100 degrees fahrenheit hotter than organics under regular daily usage).

Note that sintered pads running on stainless-steel rotors is probably
the best brake for all around usage (comes up to temp fast, can take a
high heat and occasional loading, works well in rain and the wet),
although organics provide faster stopping power (esp. in conjunction
with cast iron rotors) when they are in their 'idealized' environment
(run hot and kept hot, such as in racing applications; they don't work
nearly as well in wet environments, nor when they haven't come up to
temp yet). Never use sintered pads with cast iron rotors -- it's a
recipe for disaster.

There is a wonderful technical explanation with complete details on
various material designs, material-interactions (different pad/rotor
materials), the actual surface-surface friction transfer of different
materials and where/when different kinds of pads are best for your
usage in the Dec 2002 issue of "Sport Rider" magazine (pages 66 - 72,
titled "Science Friction", magazine cost: $3.99). The story is written
about and for a motorcycle-riding audience, but is just as applicable
to your purposes.

Best Wishes,
=-= Marc Glasgow

On Thursday, January 2, 2003, at 09:42 PM,
s-car-list-request at audifans.com wrote:

> What kind of pad will make
> her not squeal? :-)

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