"Warped" rotors -- actually rotor(s) with a hard spot, so they wear
unevenly. Pedal will pulse, too.
However, there are also several other things that can cause this: Worn
steering linkage (tie rods go first on GM trucks, but the drag link can
be bad, too), ball joints, worn suspension bushings, etc.
Check for uneven tire wear, either on the insides or outsides of the
front tires, and verify that the steering linkage isn't sloppy (jack
one front tire off the ground and push/pull at 3 and 9 o'clock as if to
steer the tire -- if it clunks and moves, something is loose.
Certainly, if you have poor braking, you at least need new pads. On
that vehicle, I would have the rotors shaved to make sure they are true
-- you need only remove a few thousandths to get any hard spots off.
Hopefully they aren't badly gouged from running the pads too thin --
don't remember if those are riveted or adhesive type pads -- rivets
will run deep grooves in the rotors. Clean the slides, lubricate as
specified (don't know that either), and verify that floating calipers
don't have any side to side play on the pins and bushings, if so,
replace the pins and bushings. Ditto if the boots are torn or the
caliper is stiff.
You will probably need a pry bar to check for loose bushings on the
control arms.
Diagnose properly before repair -- my experinece with GM light truck
chassis would lead me to suspect a bad (sticking) caliper and/or warped
rotors, but check everything else, too.
Peter
