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Re: Coupe Quattro rotor warpage

Good explanation, thanks for setting me straight, Pete. I can confirm the
water held in the holes bit. My Cressida became virtually unsafe last
October during the rain storm that flooded Boston; it was like the brakes
just went away during, and even immediately after, travelling through a

Sean Ford
Newton-Wellesley Hospital
Newton, MA  02162 (USA)
'92 Audi 100CS 5spd  16K miles (and counting!)
'89 Suzuki Katana 600 14K miles (and hibernating)

> From: Pete Kieselbach <petek@pharmacop.com>
> To: quattro@coimbra.ans.net
> Subject: Re: Coupe Quattro rotor warpage
> Date: Tuesday, March 11, 1997 2:54 PM
> Sean wrote:
> "... Drilling rotors will only lessen the rotor mass and actually
> leads to warpage because it takes less heat to warp less mass."
>         I imagine this could become another endless thread, but what the
> hell - here's my contribution:
>         I disagree about the less mass bit.  Actually I believe that
> warping is caused by differential thermal expansion (or more likely,
> contraction - more on this later).  The less mass there is, the more
> rapidly it will cool (or heat), but as long as there is uniform cooling,
> the lower mass rotor should be no more prone to warping than the higher
> mass one.
>         It's that "uniform" cooling bit that I believe is the culprit
> If you apply uneven cooling to the rotor, part will cool (thereby
> shrinking) faster than the rest, and voila: one warped rotor.  Where does
> this non-uniformity come from, you ask?  The best guess I've heard of is:
> the brake pads (as in leaving the pressure on the brakes while stopped
> after hard braking).
>         Any better theories out there?
>         By the way, I put drilled rotors on a Scirocco I had awhile back,
> but would be hard pressed to say that they made any improvement in
> performance, though they were loud!  I suspect that new un-drilled rotors
> would've worked just as well.  Another tidbit I heard, but can't confirm:
> all those holes can hold water and make the brakes slower to dry out
> going through a puddle...
> '90 100q (161K, great brakes)
> '95 Merc Villager (35K, warped rotor)
> '73 Norton 850 Commando Roadster (41K, might stop in time)
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
>       Peter Kieselbach                       ... the look in his eye
>       Pharmacopeia, Inc                     seemed to say to the sky
>       101 College Road East                 "how to amuse them today?"
>       Princeton, NJ  08540
>       (609) 452-3788 (phone)
>       (908) 422-0156 (fax)
>       petek@pharmacop.com
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