Squeaky disc brakes

Sorting out your thrunge brackets, fettling your inter-rositers and even stuff about bike parts.
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The Rookie
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Re: Squeaky disc brakes

Postby The Rookie » Tue Jan 22, 2013 21:18 pm

How about a certain exmaple where decontaminating it (as far as possible being the only change) fixed it, I've never known it do diddly.

That's the point PJ, people always trot out contamination, but from an engineering viewpoint it makes no sense, so if it can't be shown reasonably to be true (empirically or by testing), then lets stop giving poor advice (If it is that).......

heez29
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Re: Squeaky disc brakes

Postby heez29 » Wed Jan 23, 2013 02:50 am

The Beginner wrote: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.


I had a customer that lubricated his Elixirs because they were "too dangerous".


Lagrange
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Re: Squeaky disc brakes

Postby Lagrange » Wed Jan 23, 2013 09:33 am

The Beginner wrote: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.


..which would make the wavelength 34mm which is perfectly feasible in the circumference of a rotor.

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The Rookie
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Re: Squeaky disc brakes

Postby The Rookie » Wed Jan 23, 2013 09:42 am

Oh dear god, think about it, your answer is non sensical in the extreme

Say rotor has 2 contaminated patches, pedaling at 120rpm with a 2:1 gear ratio which is mid cassette on a 32t chainring (so rear wheel spinning at 240rpm). thats 480 input pulses per minute, or 8Hz....a long way from 10,000!
The 34mm would only be relevant if the if the surface of the disc was at the speed of sound, I'll pay to watch you do that.....as the tyre (and therefor bike) will be doing circa Mach 4.5.....

Too clever for your own good?

Lagrange
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Re: Squeaky disc brakes

Postby Lagrange » Wed Jan 23, 2013 09:45 am

You can justify pollution by lubricant as the source of the squeal if you draw the force diagram. Two inward pointing forces from the brakes compressing the disk. On one pad there will be a circumferential force because of friction and less so on the other because of the grease. Resolving these will give you a force vector pointing, away from your left foot which will cause the rotor to vibrate with a wavelength where npi Lamda = circumference of the rotor at the point of the friction. n an integer or it would not resonate. The vibration is parallel to the axle...ish.

The input can be anything - beat a drum once and it will resonate with a frequency - beat it with a frequency of 480 per minute and it will still sound the same. The accoustics are associated with the rotor and not the disc which is exciting it.

Lagrange
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Re: Squeaky disc brakes

Postby Lagrange » Wed Jan 23, 2013 09:48 am

Wavelengthxfrequency = speed of sound...work it out. That is not even o level physics.

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The Rookie
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Re: Squeaky disc brakes

Postby The Rookie » Wed Jan 23, 2013 12:10 pm

I know it...the point is to get to what you said the bike had to be doing Mach4.5 which was also O-level physics....

As for your second one 'inward forces' Where on what? Differece front and rear, you think the frame resonates at that sort of frequancy, try it, they don't!

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Thelonegroover
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Re: Squeaky disc brakes

Postby Thelonegroover » Thu Jan 24, 2013 11:26 am

Just to add another spoke, it's only my front brake that sqeals, the rear has always been quiet. I think I might try swapping the disks. However, I suspect the problems is the different frequency properties of the fork compared to the rear triangle.
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The Rookie
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Re: Squeaky disc brakes

Postby The Rookie » Thu Jan 24, 2013 11:45 am

Different stiffness wheel mounting (fork v frame), different caliper adaptor different stiffness caliper mounting (fork v frame), different hub, that's assuming you have the same pads and disc.

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Thelonegroover
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Re: Squeaky disc brakes

Postby Thelonegroover » Thu Jan 24, 2013 14:11 pm

Yeh, different just about everything apart from the disk and pads themselves. The point I was trying to make was: there are numerous factors that control squeal, not necessarily the pads and disk or what may or may not be on them.
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BikingBob
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Re: Squeaky disc brakes

Postby BikingBob » Thu Jan 24, 2013 16:04 pm

Blame it on Wiggle, always works for me :)
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Thelonegroover
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Re: Squeaky disc brakes

Postby Thelonegroover » Fri Jan 25, 2013 08:27 am

I'm tending to find I can use my sqeal as a sort of automatic warning bell, when coming up behind someone! So it can be quite useful.
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cooldad
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Re: Squeaky disc brakes

Postby cooldad » Fri Jan 25, 2013 08:51 am

May I suggest wearing ear plugs and ending this somewhat bizarre thread.
When the discussion includes wavelengths, lambda, and the relative frequencies of forks and rotors it's gone a bit too far.
It's slowing a bicycle FFS. Just stick your foot in the spokes.
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mrmonkfinger
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Re: Squeaky disc brakes

Postby mrmonkfinger » Fri Jan 25, 2013 14:01 pm

I had some Elixir 5s on one of my bikes. They made no noise at all.

The same brakes (same disc, pad & mount bracket) on a different bike & wheelset, honk like a trumpeting elephant in the mating season.

SpeshFSR
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Re: Squeaky disc brakes

Postby SpeshFSR » Tue Jan 29, 2013 15:39 pm

I've only experienced this a few times and it was after putting fresh pads in.
I think it's possibly due to the pads resonating in the caliper.
I put some copper grease on the back of the pad and reinserted into the brake caliper making sure not to get any grease on the pad material or disc and it stopped the squeal.
HTH


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