Author Topic: Disk brake squeal  (Read 933 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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Svend

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Re: Disk brake squeal
« Reply #15 on: September 05, 2012, 12:20:31 am »
Epic's description of this procedure is far better than mine.  Do what he says and you'll be fine.   8)  And let us know if you've cured the offending noise.

BTW, another little tip that may come in handy:  if the pistons are sticking, you can often free them up by removing the pads and cleaning around the piston body (sliding part) with a Q-tip soaked in brake fluid.  Make sure you use the same fluid as in the brakes themselves to ensure that the rubber seals won't be damaged.  The fluid not only cleans, but also lubricates the piston and cylinder.  Carefully press the piston back into the cylinder with an appropriate tool that won't damage the piston face.  Finish with a dry Q-tip to get rid of the excess fluid so it won't attract more dirt and contaminate the pads and rotor.


jim-ratliff

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Re: Disk brake squeal
« Reply #16 on: September 05, 2012, 07:01:08 am »
Svend, don't be so self-deprecating  :o .  Using the brake to center the rotor was a revelation, and once you said it I wondered why I wasn't smart enough to think of that. I have adjusted the brakes on my bike when I changed wheels, and had dealt with the caliper wanting to walk around, but I had been visually centering the caliper on the rotor.

That (the Q-tip) sounds like a good annual end of the year procedure. 
Before the piston starts sticking.
« Last Edit: September 06, 2012, 09:58:13 am by jim-ratliff »
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Svend

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Re: Disk brake squeal
« Reply #17 on: September 05, 2012, 07:33:06 am »
I don't think a stuck piston is the problem for Lynn's bike.  I was just putting that little tip out there for you to use if ever the need arises.  I've had to do that a couple of times -- both on bikes owned by my father in law that were ridden infrequently (he owns a lot of bikes).  Definitely a good end-of-season PM procedure.  But, while you've got your head under the hood of Lynn's GT, you might as well do a full brake service, eh?  ;D

« Last Edit: September 05, 2012, 08:30:54 am by Svend »

Svend

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Re: Disk brake squeal
« Reply #18 on: September 05, 2012, 09:03:51 am »
Jim, before you do anything to the brakes on Lynn's bike, do make sure that the wheels are properly aligned in the frame and fork.  If even slightly off, that will be enough to cause a rotor to rub on the pads when no brake is applied.  The fix might be as simple as that.....


jim-ratliff

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Re: Disk brake squeal
« Reply #19 on: September 05, 2012, 06:18:29 pm »
After an extensive road test on her bike (2 blocks) Lynn's brakes appear to be fine after adjusting the caliper per the excellent advice here.
Thank you.
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Svend

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Re: Disk brake squeal
« Reply #20 on: September 05, 2012, 08:21:17 pm »
Good one.  Glad it was an easy fix.  Hope she gets on the bike soon....


jim-ratliff

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Re: Disk brake squeal
« Reply #21 on: September 05, 2012, 08:47:11 pm »
Good one.  Glad it was an easy fix.  Hope she gets on the bike soon....
I'm hoping that she can figure out how to STAY ON the bike once she is able to start riding again.   ;D
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jim-ratliff

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Re: Disk brake squeal
« Reply #22 on: September 07, 2012, 09:25:37 pm »
Well, the disk brake problem has been identified -- not by me but by the shop after Lynn requested that we escalate the issue to a higher authority.  Their analysis -- there were no pads in the caliper (AT ALL). So no spring to push the pistons back into the caliper. How the retaining pin came out is unknown.
A bit embarassed not to have noticed, but i just never imagined that the pads could just fall out and didn't notice -- even though it was very obvious once it was pointed out.   :o
Here's hoping that no more damage to pistons or seals has been done.
« Last Edit: September 07, 2012, 09:29:43 pm by jim-ratliff »
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Svend

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Re: Disk brake squeal
« Reply #23 on: September 08, 2012, 07:50:50 am »
Gosh Jim, that is an odd one. I'm not familiar with Shimano brakes, so don't know how solid the retaning clips are, or how they could allow a pad to just drop out. Did you have the wheel off at some point?

Not sure if you do this, but when you have a wheel off, it's a good idea to shove a little shim in between the pads to prevemt someone from squeezing the brake lever and pushing the pads together. Not intended to keep pads from falling out, but if Shimano's are known for that, then this might prevent that too. 

I'm sure the shop tech checked this, but was there damage to the rotor from the piston scraping on the disk? Worth a quick look...


jim-ratliff

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Re: Disk brake squeal
« Reply #24 on: September 08, 2012, 10:05:27 am »
Will check the rotor.
I know about the problems of hitting the brake lever with no wheel on. But i don't feel that is the root. There is a retaining pin that goes through the caliper body and the brake pad clip, and the pin has a spring retaining clip. I assume something caught the retaining spring and pulled it off, allowing the retaining pin to work it's way out. Oh well, we learn what to beware of from past experiences.
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jim-ratliff

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Re: Disk brake squeal
« Reply #25 on: September 18, 2012, 07:22:39 pm »
Final post. Brakes pads were replaced, no further damage to pistons or seals.

Looking forward to getting my biking buddy back on the bike in a couple of more weeks, but probably very gradually. Sitting on the bike seat was the most painful thing she encountered. She may be my "Bronx Belle of Puckish Wit and Charm" but she's also been a pretty tough chick thru this broken pelvis ordeal.
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Svend

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Re: Disk brake squeal
« Reply #26 on: September 18, 2012, 07:39:23 pm »
Wish Lynn all the best.  She'll be back riding soon.  There are still plenty of biking days left until the snow flies.

Keep those brakes in good shape!


jim-ratliff

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Road bike disk brakes
« Reply #27 on: October 25, 2012, 05:34:20 pm »



a very interesting article about the challenges facing road bike disk brakes. i still think they are coming.

http://velonews.competitor.com/2012/08/bikes-and-tech/technical-faq/technical-faq-throwing-ice-water-on-road-disc-brakes_235280
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epic

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Re: Disk brake squeal
« Reply #28 on: October 25, 2012, 06:10:37 pm »
15 years ago they were saying all of those things about disc brakes for mountain bikes.

One of the funny things is that people keep talking about weight. Weight when we live in a world where racers have to ballast their bikes to meet minimum weights anyway. Wouldn't it make more sense to have heavier more effective brakes than a couple of lead weights bolted under you bottle cage?

jim-ratliff

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Re: Disk brake squeal
« Reply #29 on: October 25, 2012, 06:33:29 pm »
Agreed. I would gladly carry the extra weight and wind resistance to have hydraulic disk brakes.
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Svend

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Re: Disk brake squeal
« Reply #30 on: October 26, 2012, 08:21:38 am »
Jim, way back in this thread, before you discovered the missing pad, Epic and I talked about centering the brake calipers and straightening rotors.  I just came across this video that shows a few easy methods to do both tasks:

http://www.mountainflyermagazine.com/view.php/macky-franklin-blog-centering-disc-brakes.html

Something to file away in your bookmarks for future reference.

FWIW, the Avid brakes on my wife's bike seem to be susceptible to getting out of center, as I have to do this frequently.  I think I'll bump up the torque setting a bit to make the calipers tighter to see if that will fix it.  Very annoying to have to do this once a month.

« Last Edit: October 26, 2012, 08:24:31 am by Svend »

jim-ratliff

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Re: Disk brake squeal
« Reply #31 on: October 26, 2012, 09:15:21 am »



Svend:
thanks. One of the other tips I got from the local bike shop is to just insert a business card between the rotor and the brake pad on the side that's rubbing (without loosening the caliper) and clamp the brakes as a way of getting that piston to retract a bit more.  I've done that a time or two with success -- however, it didn't help much when Lynn's pads were completely gone.
« Last Edit: October 26, 2012, 09:18:43 am by jim-ratliff »
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Svend

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Re: Disk brake squeal
« Reply #32 on: October 26, 2012, 09:34:31 am »
Good tip.  But how do you slide the card in if the pad is tight against the rotor? Bend the rotor slightly by hand until it slips in?

One thing is for sure, on all our next bikes, we will have QR15 thru axles.  I think half of these problems are caused by things getting misaligned by the 9mm QR off/on/off/on thing.  There will be far less fiddling around....


jim-ratliff

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Re: Disk brake squeal
« Reply #33 on: October 26, 2012, 09:57:10 am »
Good tip.  But how do you slide the card in if the pad is tight against the rotor? Bend the rotor slightly by hand until it slips in?

Hmmm. Good question.  I've always been able to hold the card (or a similar piece of heavy paper) against the rotor and rotate the rotor and get the card to go under the pad with the rotor. So yes, that may be displacing the rotor to the side a little bit as it rotates?
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Svend

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Re: Disk brake squeal
« Reply #34 on: October 26, 2012, 10:07:22 am »
Probably the rotor is not perfectly true (most aren't), so you're slipping it in at a bent spot.  Regardless, it's a nice quick fix that doesn't need any tools.  Good for trailside.  Thanks -- I'll definitely use that one.

However, eventually the piston will end up back where it was, and you will have to use a proper alignment method -- loosen caliper bolts, etc....

Did you notice that in the video, he was working on Shimano brakes? So those methods will work for yours just fine.

« Last Edit: October 26, 2012, 10:15:23 am by Svend »

jim-ratliff

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Re: Disk brake squeal
« Reply #35 on: October 26, 2012, 11:11:54 am »
Yep, the rotors looked very familiar --  same Shimano XT as mine. Method 1 was the same as you and Epic described. Method 2 was an interesting adaptationof that.
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