Squeaky disc brakes

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JackPozzi
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Squeaky disc brakes

Postby JackPozzi » Sun Jan 20, 2013 14:03 pm

I'm a new MTBer in need of help please! Recently bought a 2nd hand MTB with hydraulic discs and the front is very squeaky when applied, on a road bike I'd just adjust the blocks to a slight angle to get rid of this but with discs I haven't got a clue. Is there an easy remedy (or even a non-easy one) please?

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Ouija
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Re: Squeaky disc brakes

Postby Ouija » Sun Jan 20, 2013 14:08 pm

The rotors need cleaning. They've got a small amount of grease on them (which causes the squealing noise). Use a bike specific degreaser on them and then wipe them clean. Probably have a bit of grease on the pads as well, but this will come off after a couple of uses/cleans.

JackPozzi
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Re: Squeaky disc brakes

Postby JackPozzi » Sun Jan 20, 2013 14:09 pm

Sounds nice and easy, thanks very much :D

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nicklouse
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Re: Squeaky disc brakes

Postby nicklouse » Sun Jan 20, 2013 14:13 pm

it does really depend on the type of noise you are getting have a read.

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cooldad
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Re: Squeaky disc brakes

Postby cooldad » Sun Jan 20, 2013 14:16 pm

Maybe, or they just squeal sometimes, lots do depending on weather, pad compound etc.
How do they stop you? If they work fine, leave them.
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The Rookie
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Re: Squeaky disc brakes

Postby The Rookie » Sun Jan 20, 2013 16:06 pm

Grease tends to stop brakes squealing, stops them working all together as well of course, despite it often being said that it causes squeaking, if you think about it it's very unlikely.

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70\'sPenguin
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Re: Squeaky disc brakes

Postby 70\'sPenguin » Sun Jan 20, 2013 17:01 pm

Invest in a small bottle of IPA (not the beer) from fleabay. Cleans rotors really nicely. If i were you i would get some new pads, seeing as you got this second-hand. No matter how much cleaning you do, if the pads are contaminated, you will still get squeal. Sintered squeal a lot. Ive found Kevlar ones have made my life so much quieter (better stopping power too). Superstar components sell em. I get mine from discobrakes.

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The Rookie
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Re: Squeaky disc brakes

Postby The Rookie » Sun Jan 20, 2013 17:20 pm

Can someone explain why they think contamination causes squealing? Logically it does the opposite, no friction, no noise....

The squeal is a resonance and is to do with the physics of the system, stiffness and weight, sintered pads are worse than organic as the pad is stiffer and has significantly less internal hysterisis (which would help abosrb the vibration). I've found avid to be worse and have thught it likley to be the CPS washers reducing the stiffness of the mounting.

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cooldad
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Re: Squeaky disc brakes

Postby cooldad » Sun Jan 20, 2013 17:31 pm

I was playing tunes on mine in the snow yesterday, different notes back and front, but it doesn't stop them working.
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70\'sPenguin
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Re: Squeaky disc brakes

Postby 70\'sPenguin » Sun Jan 20, 2013 21:08 pm

The Beginner wrote:Can someone explain why they think contamination causes squealing? Logically it does the opposite, no friction, no noise....

The squeal is a resonance and is to do with the physics of the system, stiffness and weight, sintered pads are worse than organic as the pad is stiffer and has significantly less internal hysterisis (which would help abosrb the vibration). I've found avid to be worse and have thught it likley to be the CPS washers reducing the stiffness of the mounting.


Perhaps you could send an Email to Formula and ask them?

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Ouija
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Re: Squeaky disc brakes

Postby Ouija » Mon Jan 21, 2013 03:13 am

The Beginner wrote:Can someone explain why they think contamination causes squealing? Logically it does the opposite, no friction, no noise....


Because you get variable grip. The constant fluctuation between grip/nogrip sets up resonance in the rotor.

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The Rookie
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Re: Squeaky disc brakes

Postby The Rookie » Mon Jan 21, 2013 08:29 am

Maybe, but it makes no sense, the resonance is far more liley to come from the holes./grooves/slots in the disc, not that they are needed, I once workd ona car where you could creep along (auto) just touching the brakes and paly tunes with the squeal...

As for Formula, sounds like a handy way to divert blame prehaps!

As an engineering explanation contamination doesn't stack up as obviously as just a resonancae through hitting a resonant frequancy....my lightweight aligator squeals very readily, where the replacement Avid G2 didn't, same pads, both on cleaned disc, so contamination not possibly an issue.

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Pesky Jones
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Re: Squeaky disc brakes

Postby Pesky Jones » Mon Jan 21, 2013 09:48 am

To be fair it does sound wierd that grease would cause squeaking - if there was the tiniest bit of grease of lubrication to the pads or rotor, surely you'd feel it in performance. More likely to be bad weather or dirt or maybe a small stone or maybe its just your pads.

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Thelonegroover
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Re: Squeaky disc brakes

Postby Thelonegroover » Tue Jan 22, 2013 09:09 am

We have four bikes, all with different disk brakes: Avid Elixir 5, Shimano 575, Shimano XT and Formula RX. The Avid Elixir 5s are the only ones that squeal.
I’ve cleaned all eight disks exactly the same with methylated spirit. I’ve tried organic and sintered pads in the Avids, but can’t stop them squealing. They work perfectly though.
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Uli
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Re: Squeaky disc brakes

Postby Uli » Tue Jan 22, 2013 10:23 am

As mentioned above disk squealing is caused by resonance due to interval periods of grip and lack of it (Ouija's post). It is very often caused by contamination, water, compound uneven wear and so on. but as long as they work fine I don't bother (usually stops after few good stops anyway). With current weather, bike cleaning etc they do get contaminated to certain degree pretty quick so keep them quiet would require detailed rotor cleaning after every ride and new set of pads every couple of rides. No time for this :)

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The Rookie
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Re: Squeaky disc brakes

Postby The Rookie » Tue Jan 22, 2013 12:06 pm

Uli wrote: It is very often caused by contamination, water, compound uneven wear and so on.

Hypothesis or fact, if the latter, evidence please?

I stated what I was saying was belief, you are saying it as a fact, so you need to back that up!

Uli
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Re: Squeaky disc brakes

Postby Uli » Tue Jan 22, 2013 14:57 pm

Well it is fact. You get uneven force applied by pads to the rotor while it spins. Rotor starts oscillating and squeals. The force difference can be a result of listed above as they cause sort of friction material slippage. It could be also due to friction material differences, dust and anything else getting between brakes and rotors. In more details it is the way how pads "bite" into the rotor and then let it go but that is more complex physic which I don't remember much.

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The Rookie
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Re: Squeaky disc brakes

Postby The Rookie » Tue Jan 22, 2013 14:59 pm

So it's your belief it causes squealing, a belief I don't share, so you need some evidence.....the frequancy of that input is far to low to be anywhere near the 10,000 Hz (ish) of a squeal.

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Pesky Jones
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Re: Squeaky disc brakes

Postby Pesky Jones » Tue Jan 22, 2013 15:18 pm

Getting a bit deep now... theres infinite reasons that could cause it. The only thing that can be done is to mention the most probable reasons (contamination etc.) - which we have done. For all we know, it could be a mouse caught in the rotor - in which case contamination, frequencies and blah blah can do one

Uli
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Re: Squeaky disc brakes

Postby Uli » Tue Jan 22, 2013 15:27 pm

What evidence are you asking for? You could as well ask me to prove here that photons exists. You can build you own lab and test it if you don't believe. You can ask physicist for explanation with more details. I have only described the process (huge simplification) and not created a theory for it.
Human hearing range is between 20-18000 Hz (+/-) and rotor is drilled piece of metal fixed on one side only which makes it quite good oscillator. No more input from me on this.


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