Brake caliper corrosion?

[ejfluhr@austin.ibm.com (Fluhr)]

Is there a coating of some sort on the brake calipers Audi uses (G60
calipers, in particular) to prevent corrosion?

The story:  My brother pulled a set of G60 calipers from a 5000 that
was in an engine fire.  Neither Simple Green nor brake cleaner worked
very well to remove the carbon buildup.  I went out and bought a wire
brush for my drill, and it does a reasonble job (i.e. I can find metal
underneath that black coating).  Part of the caliper that was cleaned,
though, appears to be oxidizing (or reacting in some manner).  The
shiny gold-ish color metal is turning a sickly-looking gray.  I was
wondering if the wire brush has removed some kind of coating which will
make the caliper more prone to rusting.

Thanks,
Eric
'85 Coupe GT
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Eric J. Fluhr                                Email:  ejfluhr@austin.ibm.com
630FP Logic/Circuit Design                   Phone:  (512) 838-7589
IBM Server Group                             Austin, TX