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disc brake grabs at one place



 
 
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  #1  
Old November 2nd 18, 05:46 PM posted to rec.bicycles.tech
Ned Mantei[_2_]
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Posts: 66
Default disc brake grabs at one place

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
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  #2  
Old November 2nd 18, 09:22 PM posted to rec.bicycles.tech
[email protected]
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Posts: 334
Default disc brake grabs at one place

On Friday, November 2, 2018 at 9:46:09 AM UTC-7, 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


Check the air pressure in your suspension fork. I think that you'll find one fork low on pressure.
  #3  
Old November 2nd 18, 09:33 PM posted to rec.bicycles.tech
AMuzi
external usenet poster
 
Posts: 9,779
Default disc brake grabs at one place

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.

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971


  #4  
Old November 2nd 18, 10:27 PM posted to rec.bicycles.tech
JBeattie
external usenet poster
 
Posts: 3,439
Default disc brake grabs at one place

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.
  #5  
Old November 3rd 18, 03:05 AM posted to rec.bicycles.tech
[email protected]
external usenet poster
 
Posts: 260
Default disc brake grabs at one place

Brake cleaner dissolves rubber seals and lifts paint. I would recommend using automotive paint-type grease and wax remover instead (e.g., Dupli-Color Grease and Wax Remover; there are several other brands). It is specially formulated to remove grease without attacking paint or rubber.
  #6  
Old November 3rd 18, 07:30 PM posted to rec.bicycles.tech
Joerg[_2_]
external usenet poster
 
Posts: 5,553
Default disc brake grabs at one place

On 2018-11-02 09:46, 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.


Sometimes mine become sightly grabby when too much vegetation has been
"pureed" through there. Then I just keep on riding until that goes away.

Surprisingly the cheapest brake pads (Hangzhou Novich) perform best and
grab the least. In the ads they say ceramic-based. I am not sure whether
that's true but those last 1000mi on the front while the 6x as expensive
ones from the bike shop are gone after 500-600mi and shudder more in a
dirty environment.

Currently running two 8" Shimano ST-66 rotors, Promax Decipher calipers
(not a high end caliper), DOT-4 fluid, Novich pads. Stops on a dime.

--
Regards, Joerg

http://www.analogconsultants.com/
 




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