Dennis Lambert wrote:
>
> Carl,
> Since the pistons don't contact anything except the seal in the grove, ultra
> smoothness shouldn't be a factor. Actually, the pistons only travel
> fractionally when the brakes are applied; mostly just the seal flexes. When
>the
> brake pedal is released, and the pressure is gone from the piston, the seal
> returns to it's original shape pulling the piston back away from the rotor
>with
> it - this is what prevents the pad from remaining in close contact with the
> rotor. At least this is what I've been told by a mechanic that's been in the
> business for a long time.
True as far as it goes. Chromed pistons have quite a good surface, but,
over time, grit can cut that surface a bit, rust starts and that can
promote leakage. Stainless, provided it is of the correct grade, will
eliminate the rust problem (not true of 409 and similar grades, so if
someone says, "stainless pistons," it doesn't mean rust is gone
forever). Chromed pistons will wear better until the surface is broken.
Good stainless won't promote pitting from rust under a scratched
surface.
Cheers.
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