Scott,
Pull off a wheel, and put either a:
1. dial indicator 2. layout scribe on a stand or 3. small camera tripod handle
up close to the face of the disc, zero it out (if applicable) and spin the disc
slowly by hand. If you can see, just by eye, the clearance change as the
disc goes around, then the disc is warped, and should be either turned or
replaced... (insert expert opinion here). If the runout is in the low-single-digit
thousanths, then the other possibilities rise on the list.
Wheel bearing play or wear could also be a culprit, as it would allow the disc assembly
to wobble on the spindle.
Usually rotor warpage comes from overheating due to multiple braking events --
like racing, or coming down the hill from Kentucky into downtown Cincy. I guess it
depends on how hard your sudden braking was, as to whether it could warp a rotor
in just one application.
I have read that, if you're into your brakes heavily, and then come to a full stop,
don't just sit at the light for 3-4 minutes with the brakes on. Rather, stop a car length
back, and then creep up in short segments, with 10 seconds or so max stop duration.
Why? Apparently, pads can act as a heat sink to hot brakes, and draw the heat out
of the disc unevenly, when left in contact for the duration of a stoplight. This uneven
cooling can lead to disc warping. A 10-second duration of stop in any one place
is evidently not enough to cause a problem. (This is according to some econo-tuner
magazine my son reads... so it must be true!)
Ken
