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>From: Toby Erkson <Toby_Erkson@ccm2.hf.intel.com>
>Also, make sure there is the ever-so-slightest wobble when securing the
>rotors to the spindle. It's this wobble that "spanks" the disc pads back
>into the caliper and keeps them from constantly rubbing.
A small amount of play is necessary to assure that the bearings are never
subjected to excessive loads, but a caliper in good shape does not need to
be slapped back into place. If you feel the sides of the pads while someone
presses and releases the brake pedal you can feel the pad press in and draw
back as pressure is released. The restoring force comes from the square
cross section O-ring in the caliper bore; it deforms slightly if the piston
moves in a small amount and pulls the piston back when pressure is released.
In other words, the piston doesn't slide through that seal most of the
time, seal just bends and moves with the piston. For larger travel,
however, as in accomodating for wear, the piston slides within the O-ring.
This is the best way that I know of to inspect calipers to see which pistons
are seizing up. They seize up so easily because that only requires enough
friction to keep the o-ring restoring force from pulling the piston. This
is also the reason that disk brake master cylinders don't have the residual
pressure valves that are standard with drum brakes. (Hence the blue banded
"special" 66 caliper--the only single circuit disk brake year.)
Jim
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Melissa Kepner Jim Adney
jadney@vwtype3.org jadney@vwtype3.org
Laura Kepner-Adney
Madison, Wisconsin
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