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My disc-brakes on my mountain bike sing/scream when I brake. I have tried to clean them, but it didn't work. Should I replace the disks or the brake pads? Is there a better (cheaper) way to fix this.

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There's nothing wrong with screaming brakes. Some makes/models scream more than others, but it's quite normal. There's also a ton of other, similar questions. Check the "related" section to the right. –  arne Dec 5 '13 at 8:11
    
Maybe the pads are not bedded in properly. New pads take a dozen of very hard brakings to stop screaming and begin braking. –  Vorac Dec 5 '13 at 9:07
    
possible duplicate of How do I prevent disk brakes from squeaking in the rain? –  Benedikt Bauer Dec 5 '13 at 10:11
    
possible duplicate of how do i stop my Formula disk brakes from squealing –  mattnz Dec 5 '13 at 20:18
    
@BenediktBauer - Not a duplicate. It doesn't just squeak in the rain. –  user2670468 Dec 6 '13 at 7:06
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3 Answers 3

up vote 6 down vote accepted

In short, squeaking brakes are caused by the sound of your pads sticking then slipping increadibly quickly, rather than applying presssure to your discs smoothly.

Solution: Sometimes these problems can be a right pain in the butt. Sometimes your brakes need time to bed in, sometimes, as you know, your discs just need cleaning, or importantly, drying. But if that doesn't work you need to rough up your discs. You can get products with abrasives in them just for this purpose, or, less expensively.. I know many people have had success with very fine sand paper.

Give that a try before replacing your discs.

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How fine is very fine sandpaper? 800? Btw +1 for the exhaustive run-down. –  Vorac Dec 6 '13 at 12:51
    
150 to 200 grit is ideal in my view. –  rossagator Dec 6 '13 at 14:22
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Here is a tip for you - putting a smudge of copper grease on the BACK of your pads can reduce the noise. It may still be there until the brakes are properly bedded in, but I have found it does make a difference, especially under lighter braking.

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I agree entirely. My advice would be do this if everything else has failed and be super careful not to ge it on the front of the pads.. That way lies madness, dudes. Also, just to emphasise yoir point to the people.. It has to be COPPER grease as you said, standard grease wont do! Good suggestion. –  rossagator Dec 17 '13 at 7:31
    
What do you mean by madness? I need to know if madness means death due to brakes not working anymore. –  user1881215 Jan 20 at 8:42
    
Madness will only occur if you manage to get grease on braking surfaces. Applying to the BACK of the pad is perfectly safe and will reduce noise. Just make sure it doesn't go anywhere else. –  Alan Shortis Jan 21 at 13:52
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assuming your brakes are clean, well maintained, aligned, right and tight; sounds like you need to get the brakes HOT to help them bed in. Find the steepest tarmac deserted road that you know. Going at about 5-10 MPH, do an emergency stop on one brake only. On no account lock the wheels and have overriding regard for staying under control. Do this a few times, say 7 or 8, and get the brake good and hot. Repeat the procedure for the remaining brake.

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