Author Topic: Disk brake squeal  (Read 934 times)

jim-ratliff

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Disk brake squeal
« on: August 22, 2012, 03:34:19 pm »
Lynn's bike has Shimano center-lock disk brakes (hydraulic). Her rear wheel has adopted an annoying squeal when not in use (but still has great modulation and stopping power), and I would love to be able to tell her what she needs to do in order to get rid of it.  We've tried inserting cardboard on each side of the rotor to see if forcing the pad back from the disk a bit but to no avail (I was told this is the recovery trick if you hit the brake lever while there's no wheel in the bike).

Share the wealth of knowledge that I am sure is out there. The noise is so loud, I'm expecting to hear Deliverance banjo music around the next corner.  :'(   
 
I had a similar problem on the front of my bike (also center-lock, but XT instead of SLX) and wound up replacing the center lock with screw on rotor's from Avid and never looked back. Google said that XT disks were prone to squealing in temperatures below 40 degrees, which it was.

Midwif's last two falls (including the biggie) have both been on the right side of the bike and the brakes are on the left, so I assume that's not the problem.  We did haul the bikes to Canada upside down (that left more room for luggage) -- is that bad for hydralic's?  Even when squealing, the brake isn't noticeably dragging.

I did tell her that oiling the brake to get rid of the squeal probably wasn't an optimal solution?  ;D
« Last Edit: August 22, 2012, 03:39:47 pm by jim-ratliff »
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epic

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Re: Disk brake squeal
« Reply #1 on: August 22, 2012, 07:17:54 pm »
Are the bolts that hold her brake caliper onto the frame 51mm apart or 74mm apart?

Svend

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Re: Disk brake squeal
« Reply #2 on: August 22, 2012, 09:52:58 pm »
Jim, am I reading this right? That the brakes squeal when no pressure is applied to the lever? But do not squeal when actually braking?

I had an extremely loud squeal from the rear brake on my Fisher (Avid Juicy 5), and I tried many things to get rid of it, to no avail, until I tossed the stock Avid pads and put in Jagwire ones. Problem solved.  And loud it was -- sounded like a 1950's city bus moving through the woods; animals and birds were fleeing in terror.

For Lynn's bike, there could be a number of causes -- contaminated pads or rotor; worn pads; bent rotor; calipers out of alignment; rotor bolts unevenly torqued.

Things to check:  bent rotor (spin the wheel and look for a wobble); worn pads (there should be a couple of millimeters material left on each side).  The other causes are more difficult to spot, so just read below....

Here are some things to try, with the caveat that I am not familiar with Shimano brakes (should be some cross-over, though):

1) align the calipers by loosening the mounting bolts, squeezing the brake lever 5 or 6 times, and then holding the lever (pressing the pads to the rotor) while torquing down the bolts to the specified value, alternating between bolts -- tighten one a little, then the other, back and forth until the torque wrench clicks (...you do own a small torque wrench, don't you? essential kit for any bike owner, esp. for carbon frames....)

2) clean the rotors with rubbing alcohol, methyl hydrate, or automotive brake cleaner; they may be contaminated with oil or grease; you can try to clean the pads too, using fine emery paper and alcohol wipe

3) loosen then re-torque the rotor bolts to their specified value, in the order required by the service manual

4) check the rotors for warp; if bent, try to straighten them (gently) using a pair of plumbers pliers; use a soft cloth to protect the rotor; or buy a rotor truing fork to do the job

5) replace the pads, if worn, or if you suspect they are contaminated but can't get them clean

Hope this helps, but post back here if none of this works.  Good luck...

Svend


jim-ratliff

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Re: Disk brake squeal
« Reply #3 on: August 22, 2012, 10:24:12 pm »
Epic:  Looks to be right about 3", so that would be closest to the 74mm choice.  ??


Svend:  Yes, squeal when no pressure, no squeal when braking and stopping power is fine. Some good suggestions otherwise, especially cleaning rotor and pads and adusting.  No rotor bolts, however, on center-lock. I think I looked for warpng or bent and the squeal isn't rhythmic with wheel rotation, but will look again.


Cleaning the pads especially, maybe there is a piece of dirt of somthing stuck to the pad.



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epic

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Re: Disk brake squeal
« Reply #4 on: August 23, 2012, 05:36:57 am »
So it sounds like you have 74mm post mount then. Assuming everything is cleanish, you're gonna want to make sure the brakes are centered. You probably have one pad just touching the rotor. Can I assume the brakes are Shimano? Anyway, loosen those two bolts, jiggle the caliper around to make sure it is loose, then squeeze the brake lever. While holding the brake lever, tighten those bolts back up. Do it gently so that the caliper doesn't move while you are turning them (sometimes it tries to walk as you turn the bolts). Hopefully, you now have the same amount of space between the rotor and the pads on both sides. If not, and you still have some squealing, you can try to fudge the caliper over a little bit while the bolts are loose.

bushwacka

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Re: Disk brake squeal
« Reply #5 on: August 23, 2012, 06:22:38 am »
what svend and epic say. 95 percent of all brake problems can be resolved by recentering them.

Svend

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Re: Disk brake squeal
« Reply #6 on: August 23, 2012, 07:00:40 am »
Jim, it could also be something as simple as the entire wheel being misaligned in the frame/fork brackets. Try loosening the quick release, centering the wheel, and retighten.  Do that before you do the caliper alignment procedure; the alignment is only good if the wheel is locked in true.

If none of the above things work, it could also be that the pads are glazed (but this would show up more when brakes are applied). Use the fine blue emery paper and some alcohol to deglaze and clean them.


jim-ratliff

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Re: Disk brake squeal
« Reply #7 on: August 23, 2012, 07:50:13 am »



Thanks all.  Good info.

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midwif

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Re: Disk brake squeal
« Reply #8 on: August 24, 2012, 09:22:53 am »
And the rider who was considering oiling the brakes thanks you too. :-[
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Svend

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Re: Disk brake squeal
« Reply #9 on: August 24, 2012, 03:58:51 pm »
Lynn, does this mean you are riding again? No more crutches or cane? If so, good on ya!

Great idea about oiling the brakes to get rid of the squeal  ::)  A nice even coating of petroleum jelly should work well too  ;D


jim-ratliff

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Re: Disk brake squeal
« Reply #10 on: August 24, 2012, 10:26:45 pm »
Svend:
Lynn says Thank You for the petroleum jelly suggestion.  She had been torn between Canola or Olive ooil.


Nope, she's not riding yet. Just today she is suddenly  able to get around most of the day without a crutch; I would imagine she's still a couple of weeks from being able to sit on a bike saddle.
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Svend

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Re: Disk brake squeal
« Reply #11 on: August 25, 2012, 07:50:02 am »
Gotcha - it sounded like this was a recent problem, post-Montreal.  Great news on the better mobility. Hope this means super-fast recovery from now on.  Lynn, best of luck with that. Keep on swimming!


ToddW

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Re: Disk brake squeal
« Reply #12 on: August 27, 2012, 11:39:47 am »

Be sure to prep the disk with a spray on PTFE treatment before applying the petroleum jelly -- afterwards is too late.


Svend

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Re: Disk brake squeal
« Reply #13 on: September 04, 2012, 06:05:29 pm »
Jim -- any luck fixing this problem yet? Or is the lady not yet riding? Still convalescing?


jim-ratliff

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Re: Disk brake squeal
« Reply #14 on: September 04, 2012, 08:33:52 pm »



Still convalescing, but she may try taking an easy ride this weekend.
I plan to take a look at it this week.


I'm pretty sure that you (and epic and bush) are right that it's the caliper alignement. And I had never heard of applying the brakes to cause the caliper to align itself with the disk, so thanks for that little piece.
« Last Edit: September 04, 2012, 08:40:30 pm by jim-ratliff »
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