On Friday, November 2, 2018 at 1:34:05 PM UTC-7, AMuzi wrote:
On 11/2/2018 11:46 AM, Ned Mantei wrote:
My newer mountain bike uses Shimano Ice-Tech discs (SM-RT81)
and JO4C "metal" brake pads, with DT-Swiss through-axle
wheels and XT brakes. In June I installed a new front disc
and brake pads, and neither is appreciably worn yet.

Even if the wheel turned freely except for some scraping at
the very beginning, later pads and disc would begin to
scrape again at one segment of the disc. Sometimes this
seemed to arise from just braking during a turn. Awhile ago,
after a lot of fiddling and multiple tries I was able to
bend the disc a bit to eliminate the noise and have the
wheel turn without binding. But now a very slight binding is
back on the same section of the disc. This isn't noisy, and
I might have not even noticed. However, now when I brake the
brakes grab where they bind, which feels like hitting a
little bump at every turn of the wheel.

So some questions:

Can I just ignore the brake grabbing without long-term damage?

Ms. Google suggested bending the disc to avoid scraping. Is
there some other trick? Could it be that my multiple tries
at eliminating the scraping somehow damaged the disc?

Would it be advisable to replace the disc?

Other suggestions?

Thanks for your advice.

Ned

If you myopically and carefully examine your disc find and
it's dented or warped, we would just replace it. They're
dirt cheap and plentiful. Be sure to thoroughly degrease it
with brake cleaner before slipping the wheel in place and
keep your filthy oil-laden fingers off it. We also wash pads
before installing a new disc. They are sensitive to oil
contamination.

Agreed, but the Ice-Tech (!) rotors aren't all that cheap. Neither are the Shimano shoes. Might want to take one more shot straightening and cleaning it with some disc brake cleaner. Or, in the alternative, think of it as ABS. It's a feature!

-- Jay Beattie.