Joe,
I'm on digest, so sometimes I miss the timeliness. You're right, "caliper"
was never stated. I assumed as I guess Randall did, that Scott was asking
about calipers, maybe because I've only seen options on caliper pistons,
and most (not all) master, slave, and wheel cylinder pistons these days are
aluminum. And actually, your scenario is correct for the Dunlop style
caliper where-in the seal is resident on the piston and seals against the
bore, which is the only caliper that can justify sleeving.
Didn't mean to sound critical, and I apologize if you took it that
way.
Peter C.
----
At 09:20 AM 2/12/2002, you wrote:
>Actually, When I wrote that reply, I had no intention of including disk
>calipers in that scenario. The word, caliper was not mentioned and therefore
>I think that if you exclude that, my scenario is correct, Right?
>
>Joe
>
>"Peter C." wrote:
> >
> > > Scott Tilton wrote:
> > > > I would assume that any amount of tiny pitting or rust is cause
> > > for a rejection of an used brake piston. Is this correct?
> > YES!!!!
> > Joe Curry wrote :
> > > But the piston doesn't really contact the
> > > cylinder but serves as
> > > an housing for attaching the cups that do contact the cylinder
> > > walls. So as long as the piston does not bind up and still seals
> > > the cup and/or O-rings, it will still work regardless of pitting.
> > ------
> > True only of Dunlop style calipers as on early Jaguars, early
> Datsun
> > roadsters, etc.
> > ----------
> > We need to be clear here about whether we're talking about front disc brake
> > caliper pistons, or drum brake pistons.
> > <snip>
> > For disc brakes, the seal is mounted in the caliper body, and rides on the
> > sides of the piston. Any pitting or corrosion in this area will cause
> leaks
> > and rapid seal wear.
> > Randall
> > =============
> > If I may add to Randall's note: The seal is a square-cut O-ring and is
> > designed to deflect when the caliper is pressurized and the piston moves.
> > When the pressure is released (foot off pedal) only the seal relaxing
> > releases the pad from rotor contact. (there's no return springs ala drum
> > brakes) Any pitting of the piston surface will scar the seal and rather
> > than flex, it will just scrape the piston and not assist in pad retraction.
> > This is the beginning of accelerated pad wear. Insist on new pistons every
> > rebuild (many rebuilders don't always change them) Personal preference is
> > stainless, fwiw. It's only brakes.
> > Peter C.
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