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Is it normal for disc brakes to squeal?

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Is it normal for disc brakes to squeal?

Old 06-09-05, 11:09 AM
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prop
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Is it normal for disc brakes to squeal?

I am looking at a new bike with disc brakes. I'm really excited by the bike, like everything about it EXCEPT that the disc brakes squeal when depressed hard (they are Shimano M525s). He tells me this is "normal" and that it will go away.

I did a search on this site, and even though there's a fair bit about disc squealing, most of it seems to be in conjunction with rain, and I rode it on a nice dry day.

I'm a bit concerned about whether or not I'm getting fleeced... Can anyone tell me if I should believe him or not? I did find one person on this forum who stated it was OK, and that riding down a long hill with some tension on the disc would solve the problem (supporting the "it will go away" idea), but I would feel more comfortable if others also told me this... A case of buyer's anxiety, I guess

Thanks!
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Old 06-09-05, 11:41 AM
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It is normal for new disc's to squeal, once they're broken in, it should go away.
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Old 06-09-05, 12:06 PM
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I find the squeal comes and goes. Once the pads have been broken in, squeal usually means it's time for an adjustment.
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Old 06-09-05, 09:49 PM
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525(the type I have on both of my race bikes) only squeak when seriously dirty or contaminated.
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Old 06-09-05, 09:57 PM
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Since I ride through an industrial park, god knows what kind of grit and oil is stuck on my pads. They squeal if they're pressed whenver, the tone differs between light and hard but they squeal and make me sound like a truck, which is pretty cool so I'm keeping it.
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Old 06-09-05, 10:21 PM
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The only normal squeak is a high whistle sort of thing. If it is a low tone or persistent one, then that requires inspection. The most simple way to inspect for an oil-contaminated brake is to look at the rotor. Oil will make the friction surface of the rotor turn non-silver colors. Non-chlorinated brake cleaner and a pure white rag will clean the rotor well. The pads are another story.
Sometimes the pads can be saved, depending on how much material is left and how long they have been honking. The oil will fuse with the pad compound if it is allowed to melt in with use, renering the pad all but useless. If there is a log of pad left, then you can sand off some, wash it in cleaner and repeat until it wipes clean on the white rag.
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Old 06-10-05, 12:21 AM
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Repeat after me: "Denatured Alcohol is the only thing I should use to clean my rotors" Repeat this until it is ingrained in your memory
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Old 06-10-05, 01:42 PM
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I might of been the guy you read about going down the long downhill :-)
Trust me. IF they are setup correctly and if they are clean the squeal WILL go away. You do have to break them in though.
Again, setup right, clean, and broken in = excellent brakes that don't squeal.
I was just like you at first, now I am a believer.
D
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Old 06-11-05, 02:14 AM
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A dab of Coppaslip on the back of the pads might cure it. It's what you do to every other type of disc brake.
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Old 06-11-05, 02:34 AM
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Originally Posted by Raiyn
Repeat after me: "Denatured Alcohol is the only thing I should use to clean my rotors" Repeat this until it is ingrained in your memory
Denatured alcohol? Is that just another name for methylated spirits?
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Old 06-11-05, 05:23 AM
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Yep. It's just ethanol with a bit of methanol (and sometimes a few other noxious compounds) added so it's not drinkable. I've found personally that isopropynol is a better solvent for contaim problems on the rotor, it seems to be slightly less harmful to my finishes and tires when it spills.

As far as noise on the pads often it's not contaimination, it's just the TYPE of pad you have on there. Pads come in different formulations for different conditions. Some pads are harder than others and some are going to make more noise. My avid mechanicals came with pads that were AWFUL even after broken in. The current replacement set quieted down within a few brakings and is now only noisy when it's very cold or when they're wet.
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