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I am having a very loud squeaking voice in the brakes of the rear tyre. I don't know what the problem is, but I am sure it has nothing to do with rain, because it happens all the time even if it is dry.

Anybody have an idea what could the problem be and how to solve it? It makes the rear brakes kind of useless, because if I use, I will scare the people or drivers around me.

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My disk-breaks do this from time to time too. Usually it goes away after a while. I suspect it might have something to do with the break making a strange contact with the rotar. Once it wears in it may fix it. –  sixtyfootersdude Jan 22 '11 at 13:43
    
What kind of brakes are they? Disc, calliper, V? –  Scott Langham Jan 22 '11 at 14:48
    
@sixtyfootersdude, no it didn't go away. At the beginning I thought the discs were too old, so I replaced them. I have been using them for more than a month now (may be even more) and I still hear squeaking. –  Promather Jan 22 '11 at 17:27
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Oh, sorry, not disc brakes (sorry, my bad English), I am not sure what they are called, may be calliper, but they are basically two pads on the wheel itself like this: upload.wikimedia.org/wikipedia/commons/8/80/… –  Promather Jan 22 '11 at 17:29
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These are side-pull caliper brakes. The correct title for this question is something like "How do I make my brakes stop squealing?" –  Jay Bazuzi Jan 22 '11 at 18:15
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5 Answers 5

up vote 32 down vote accepted

Squealing can be reduced by "toe-in" - making the front part of the brake pad touch first.

Check out Park Tool's instructions on servicing side-pull brakes: http://www.parktool.com/blog/repair-help/sidepull-brake-service

Squealing is the result of a harmonic resonance from a slip-and-stick phenomenon, similar to how a violin bow resonates on a string. The brake pads grab the rim and are pulled forward by the force of the wheel. The arms must at sometimes jerk backwards, but if you are still braking, the arms are flexed forward again. This is repeated again and again many times per second, and this creates the squeal. Because of this, flexible and less expensive arms tend to squeal more than stiff calipers of better brakes. It is possible to reduce squeal by having the leading edge of the brake pad strike first. This tends to reduce the back and forth jerking of the arms.

But before you go trying to toe-in, make sure you're working with parts in good shape:

Examine your brake pads. If they are old and hard, worn deeply, or full of junk, replace them. Otherwise, use coarse sandpaper to take off the surface to bring out fresh rubber. You only need to take off a tiny bit.

Clean your rims. Road grime, bike lubes, and brake material all collect on your rims. Rubbing alcohol, vinegar, Simple Green, a product marketed as "degreaser" can all work. Don't let any get on the drivetrain or in the hubs. Also, you'll need rags.

True your wheels. There's no point in trying to adjust brakes on a wheel that isn't true (round and dished is good, too). And you can't true a wheel if the hubs aren't in good shape.

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Man, that looks like a very polished answer! Thanks very much, I will try it, I would have given you two votes if that's possible. –  Promather Jan 22 '11 at 19:11
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Jay's answer covers most of it and you should start with his suggestions (toe-in and greasy rims are big culprits). I'll only add two things:

  1. Brake pad type can sometimes make a difference. Kool-stop "salmon" pads are widely recommended to reduce problematic squeals.
  2. Some bike setups are more prone to squealing, even with clean rims, new salmon pads and perfectly aligned brakes. It's very unusual but I had this problem on a previous bike (V-brakes on a carbon fork).
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+1 vote from me for the first note. –  Promather Jan 22 '11 at 21:16
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The above answers cover the critical information, but I'd add that some brakes make "toe in" adjustment easy (offset washers, or other means). Some brakes require that you bend/twist the arms. For the latter, I'd recommend your local bike shop mechanic... if for no other reason that brakes are important safety equipment, and are therefore worth being looked at by a pro.

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Another cause for the noisy brakes is the brake pads not being fully tightened. In my experience such noise is more commonly seen in cantilever brakes whose mechanism is well explained by Jay Bazuzi's response.

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My bike with pull brakes, squeal like crazy...New pads, clean rims, adjusted well, still squeal. Roughed up pads, still squeal.

Now I put alittle baby powder on each side of Rim, just a dusting. I put a little baby power in palm of hand, take finger, dab in powder and rub some on the rim, each side.

Fixed my brakes, stops good and no squeals.

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I'd be interested to know if this is a temporary cure and has to be repeated. I wonder if the powder dries up any grease and grime. –  Mere Development Oct 7 '13 at 9:26
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