[Shotimes] Odd rotor stripes

[Jon Heese]

About 3 months after doing the '96 brake upgrade on my '95 SLO (using 
"barely"-used rotors and new pads), I started getting some shaking 
during braking, which got worse over the course of the next month.  I 
assumed that one or both of the rotors was/were warped, so I bought one 
Wearever $24 rotor (xref NAPA 86334) from Advance and swapped out the 
front drivers' side.  After a quick test drive, everything felt and 
looked fixed, so I figured that rotor must've been warped.

About a week later, I started feeling the shaking again, so last Sunday, 
I went and bought another identical rotor and swapped the front 
passenger side.  After a quick test drive, once again, the problem 
seemed solved, but when I got back in the driveway and looked, I saw 
that the shiny new rotor had only been swept by the brake pad in one 
stripe, about 1/2" wide, on the outer boundary (towards the rim) of the 
normal swept area.  My first thought was that the pads must have been 
worn funny and I probably needed a new set.  It was after 7pm and the 
sun was going down, so I stabled the car for the past week and pulled it 
out today to check it.

When I took it around the block today, once again, everything felt fine, 
but now the rotor is being swept in two stripes, the same outer one and 
now a 1/4" stripe on the inner (towards the wheel hub) extreme.  I took 
the caliper off and inspected the pads and they seemed prisitinely 
straight with a good 1/2" of material left.  There was no (discernible) 
slant to their wear patten.  I put everything back on and took it for 
another test spin and saw the same double-stripe rub pattern on the 
rotor.  It didn't occur to me until today to look at the inner surface 
(towards the axle) of the rotor, but when I did, I saw the same 
double-stripe pattern on that surface.

Now, the question:  What is the likelihood that my brand new (cheap) 
rotor is cupped so that the center stripe of the swept area is recessed 
from the brake pads?  Since the pattern is present on both the inner and 
outer surfaces of the rotor, I'm leaning away from my original thought 
of oddly-worn brake pads due to a misshapen old rotor.  Unfortunately, I 
didn't keep the receipt for the rotors, so either way I go, I have to 
put down $25-30.  So I figured I'd consult the oracle first.

What do you all think?

Regards,
Jon Heese