[Vwdiesel] Rabbit "High Caliper advice".

[Lee Hillsgrove]

>I wonder why brake rubber is not oil resistant.


 Well, I'm not a rubber compound expert, but apparently something about the
makeup of rubber which is compatible with brake fluid does not play well
with petroleum. I think brake fluid is not compatible with all types of
rubber which are oil-resistant, as a counterpoint. Viton (the brand name of
one of DuPont's many formulations of fluoroelastomer) may be chemically
compatible with brake fluid, but I suspect that mechanical properties and
/or price considerations prevent it's use in braking systems.

 A bit of information that might help to provide an explanation: What is DOT
3 brake fluid made of, anyway? I don't know. I do know that DOT 4 (or is it
DOT 5?) is silicone-based.


One
>interesting thing, though is the dust boots for the
>calipers are designed to pull the piston back a little
>after the brakes are applied to prevent the pads from
>continually rubbing the rotor.


 No, Nate, it's actually the square-edged piston seal which provides that
action. When the piston moves forward, it deforms the seal a little bit. As
pressure is released, the resilience of the rubber pulls the piston back
slightly. Self-adjusting!
 The dust boots we made were actually quite thin in cross-section, and would
not provide any meaningful force in either direction, especially considering
the pleats in the rubber and the distance between the ID and the OD of the
seal.


  Lee
  Oo-v-oO
  PP-ASEL
  KB1GNI