Rotor Stuph

["Al Powell" <apowell@agcom.tamu.edu>]

Phil and/or Judy Rose said, in response to Fred Munro's comments:

I've heard others also voice an opinion that resurfacing rotors is
inadvisable. When I hear it from a repair shop, my suspicion is always that
the _replaced_ rotor is simply a nice, profitable part of a brake job. But
I wonder is it possible that bad results are sometimes just from improper
turning procedures? (Too much taken off, dull cutter ...).  I can't offer
much experience, pro or con.

A comment about rotors - which some on this list could provide more 
easily than I, so I beg your indulgence - but think about the 
functions of rotors, which are to:

1)  Provide friction for stopping;

2)  Dissipate the heat generated by that stopping friction.

Relative to turning rotors, #2 is most important.  The more mass you 
dump heat into, the less that mass will be affected (temperature 
rise, thermal distortion..).  As rotors wear down, there is a minimum 
mass (functionally easured in rotor thickness) required to deal with 
the heat.  If you are marginal or drop below that mass, two things 
can happen:

1) The rotors will get hot enough from repeated uses that they may 
become SO hot that the brake pad surfaces liquefy on contact, 
creating MUCH less stopping power than normal.  This is the cause of 
"brake fade" with hot brakes;

2)  The rotor will warp from the excessive heat.

Unlike some cars, Audi minimizes the thickness of the rotors to 
reduce the total weight of the wheel assembly - and in the process, 
makes the rotors thin enough that they do not recommend they be 
turned.  Ever.  They recommend replacement along with the brake pads.

Pushing the limits on this equation is more likely to result in brake 
fade, rotors warping, etc.; the more agressive the driving, the more 
likley the result.

I'm with Fred - change them and pay the $$.  Just don't buy them from 
the dealer and you'll spend half as much (or less) on the parts.


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