WW Brain Trust - - Rear Brake squeal and vibration - HELP

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BdaGhisallo
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Joined: Wed Mar 17, 2004 1:38 pm

by BdaGhisallo

I am hoping someone here can help me solve an issue that has been bedeviling me for most of the year. I am getting the most horrendous brake squeal and vibration from my rear brake. The vibration can be so severe that I feel it vibrate through the saddle and in the top tube. I am riding an aluminum frame with an Enve 2.0 fork.

I have tried three different type of rear wheels - Enve w the textured brake track, Bontrager XXX with their laser etched brake track and a Shimano 9100 C40. They're all carbon tubs if that matters.
I have tried two different rear brakes - DA9100 and DA9000.
I have tried different brake pads. I have tried the stock pads that are supplied with the rims. I have tried the Enve grey pad on the Enve rim. I have tried SwissStop Black Prince pads on the Enve. I have tried the Shimano carbon pad on the Bontrager.
I have installed the pads flat to the rim. I have installed them with toe in, in varying degrees.
I have thoroughly cleaned and scrubbed the rims with soap and water and rubbing alcohol.
I have sanded down any pads that look to have any bit of glazing on them.
I experience the problem in both bikes I have up and running so I don't think it's anything inherent in the frame.


I never have an issue with the braking on the front wheel. I never vary from the stock pads supplied with each rim because I have no need to. I install the front pads flat to the rims and the breaking is powerful, consistent and 100% devoid of any squeal or vibration.

The vibration in the rear seems to be greater when there is more braking force at the rear. If I go light on the front brake and exert more force on the rear brake lever that is a surefire way to get the squeal and vibration set up.

I am pulling out hair that I don't have. I have never experienced this problem in all my three decades of riding and not been able to fix it quickly and easily.

Does anyone out there have any ideas?
Last edited by BdaGhisallo on Mon Dec 17, 2018 7:39 pm, edited 1 time in total.

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Calnago
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by Calnago

Wow... you certainly seem to have done a thorough job of troubleshooting. Different wheels, different bikes, different pads, different brakes and always a squeal/shudder. Normally I like a challenge like this but this is really puzzling, since you’ve swapped everything in and out, so anything I might have suggested I’m not going to. Except for one thing, and this is really the only thing I can think of...
Are your brake shoes properly torqued to the calipers?
Ok and maybe one other thing... you didn’t say if they were direct mount or standard mount, but if standard mount, check to make sure the brake nut that goes through the bridge between the stays isn’t so long that it’s “bottoming out” on its leading edge rather than fully seating itself on the lip of the bolt head against the recess of the bridge (hope that made sense). This might mean the brake caliper isn’t fully tight against the frame. And are you able to fully get say, 6 threads of the brake bolt engaged? Count the full turns.
And lastly, got any pics.
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GothicCastle
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by GothicCastle

All brakes cause vibration; because it is an aluminum frame, I assume that you’ve just found a lucky resonant frequency in your specific frame.

How tight is the brake bolt? If it is a little loose, the caliper will be able to vibrate more. I’d be tempted to put a thin shim of something that could dampen the vibration betepween the caliper and the bridge to see if it changes the noise.

BdaGhisallo
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by BdaGhisallo

Calnago wrote:
Sat Dec 15, 2018 9:35 pm
Wow... you certainly seem to have done a thorough job of troubleshooting. Different wheels, different bikes, different pads, different brakes and always a squeal/shudder. Normally I like a challenge like this but this is really puzzling, since you’ve swapped everything in and out, so anything I might have suggested I’m not going to. Except for one thing, and this is really the only thing I can think of...
Are your brake shoes properly torqued to the calipers?
Ok and maybe one other thing... you didn’t say if they were direct mount or standard mount, but if standard mount, check to make sure the brake nut that goes through the bridge between the stays isn’t so long that it’s “bottoming out” on its leading edge rather than fully seating itself on the lip of the bolt head against the recess of the bridge (hope that made sense). This might mean the brake caliper isn’t fully tight against the frame. And are you able to fully get say, 6 threads of the brake bolt engaged? Count the full turns.
And lastly, got any pics.
I was hoping that you would jump in - thanks.

Std brake calipers. I will check again but I am pretty sure that the mounting bolt nut (standard Shimano nut) is well seated and the bolt is fully tight. In fact I have to install a second toothed washer on the back of the center bolt so that the nut on the back of the pivot bolt assembly clears the seat stay. And the brake shoe bolts are plenty snug.

BdaGhisallo
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by BdaGhisallo

GothicCastle wrote:
Sat Dec 15, 2018 10:15 pm
All brakes cause vibration; because it is an aluminum frame, I assume that you’ve just found a lucky resonant frequency in your specific frame.

How tight is the brake bolt? If it is a little loose, the caliper will be able to vibrate more. I’d be tempted to put a thin shim of something that could dampen the vibration betepween the caliper and the bridge to see if it changes the noise.
This has crossed my mind. I think I will try your idea. I have some cork around and I might fashion a washer-shim out of it and see if that helps.

BdaGhisallo
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by BdaGhisallo

Well, thanks to a suggestion over at the VSalon, I just tried toeing out(!) the rear brake pads and, though based on only a short test ride, it has gone a long way to curing the problem. I never would have believed it could work if I hadn't tried but I tried both a Bontrager XXX wheel and an Enve textured rim with their respective stock pads and the vibration did not occur.

I am keeping my fingers crossed that this is a long term solution.

kode54
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by kode54

i would've never thought toe out. first time hearing that. good to know.
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Calnago
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by Calnago

Toeing “out”? You mean setting the pads so that there’s a bigger gap at the front of the brake pad than the rear? There’s something else going on if you have to do that. And your pad wear if run like that would have to be severe at the leading edge. I just can’t see that as a good solution. I see no logical rationale why that would ever work and only that it might be compensating for the real problem, whatever it is. There’s gotta be some unwanted flex or something in the system somewhere. I would cringe knowing that the trailing edge of my brake pads were the first point of contact with the rim. Think through the forces being applied under that scenario. You’d be fighting against all of them as the rotating wheel is grabbing the rear of the pad and trying to push the front away, as you use the lever to fight it back towards the rim. Versus a proper toe “in” where the front of the pad makes contact first and the rotating wheel is then “pulling” the rear of the pad to the rim, helping not fighting, your action at the lever. Any rationale has to what toeing the pads “out” is compensating for or fixing?
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BdaGhisallo
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by BdaGhisallo

Calnago wrote:
Mon Dec 17, 2018 6:44 pm
Toeing “out”? You mean setting the pads so that there’s a bigger gap at the front of the brake pad than the rear? There’s something else going on if you have to do that. And your pad wear if run like that would have to be severe at the leading edge. I just can’t see that as a good solution. I see no logical rationale why that would ever work and only that it might be compensating for the real problem, whatever it is. There’s gotta be some unwanted flex or something in the system somewhere. I would cringe knowing that the trailing edge of my brake pads were the first point of contact with the rim. Think through the forces being applied under that scenario. You’d be fighting against all of them as the rotating wheel is grabbing the rear of the pad and trying to push the front away, as you use the lever to fight it back towards the rim. Versus a proper toe “in” where the front of the pad makes contact first and the rotating wheel is then “pulling” the rear of the pad to the rim, helping not fighting, your action at the lever. Any rationale has to what toeing the pads “out” is compensating for or fixing?
I don't understand it either, and all that you described is why I dismissed this idea when I first read it. I tried every other conventional solution that I and others could think of.
Everything I have ever known about bicycle brakes tells me that this shouldn't be the solution. I am going to get some miles in on the setup this week before I am confident that this is a long term solution.

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Calnago
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by Calnago

Sounds good, but I still think even if it doesn’t shudder it’s just masking the problem by putting the vast majority of the braking force on one small section of brake pad, which effectively decreases your braking performance from what it could/should be in my opinion.
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AJS914
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by AJS914

I had a Specialized Crave aluminum hardtail that had a similar issue. It was a resonant frequency. The whole rear of the bike would shake like it was going to fall apart any second. I cured it for a while by straping a metal rod with tape to the rear seat stay. This changed the frequency and the bike wouldn't virbrate. The other thing that helped was sanding down the rotors. I got rid of the bike after that so I don't know how long that fix lasted.

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BdaGhisallo
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by BdaGhisallo

Calnago wrote:
Mon Dec 17, 2018 7:13 pm
Sounds good, but I still think even if it doesn’t shudder it’s just masking the problem by putting the vast majority of the braking force on one small section of brake pad, which effectively decreases your braking performance from what it could/should be in my opinion.
Luckily, I live in a place where I do not need to do much braking at speed. 95% of the braking here involves coming to a complete stop for a stop sign. There are no high speed descents where you need to brake around corners or hairpins and the like. There's very little altitude here and the steepest downhill will get you up to about 65kph if you pedal your legs off.

I am sure it is a resonant frequency thing. I have had bikes and brakes that squealed before (that were remedied with the conventional solutions) but never one that I could feel vibrations through the top tube and through the saddle.

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