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I have a Specialized Hardrock 2011 Disc brake mountain bike with a front brake that squeals when used lightly. It's OK if I use the brake hard - but I usually don't need or want to stop in such a hurry! I have been using the rear brake more for light braking, which is something that I don't like to do because the front brake is best for this.

It has been like this pretty much since the day I got it, so I initially put it down to needing running in. It has got a bit better with time and a few hundred miles, but not much - I try not to brake and instead carry the momentum of the bike where I can for increased efficiency.

What should I look into adjusting to stop disks squealing?

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What brand and model of disc brakes? Hydraulic or cable? –  zenbike Aug 10 '11 at 13:29
    
I've had a similar experience with a different manufacturer. –  Walter Aug 10 '11 at 15:31
    
@zenbike - if it's stock it's either the Tektro IO Mechanical, or the Avid BB5 Mechanical. My guess would be the Tektro as I have frequently seen them have squeal problems. –  Gary.Ray Aug 10 '11 at 17:37
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@Nate - Yeah, this is pretty close to that question. I'm not up on disc brakes; anyone know if these can be merged, or is there enough difference between the two models to maintain the two Q&A threads separately? –  Neil Fein Aug 15 '11 at 16:01

3 Answers 3

If they are not full floating calipers, most are not, then the problem may be the fixed side of the caliper pad has worn and you need to adjust the fixed side pad closer to the rotor (eliminate the gap)

The squeal comes from the movable pad pushing (flexing) the rotor over to make contact with the fixed pad.

This type of caliper needs periodic adjustment of the fixed pad as the pad wears.

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In my experience disc break squeal is typically a result of excessive vibration caused by one of three things:

  1. Contamination - Brake disc and pads should only be cleaned with isopropyl alcohol. Give them a thorough wipe down.
  2. Poor adjustment/loose components - Try looking at the manufacturers web site for adjustment and torque specifications. Installing and adjusting brakes is one place where a torque wrench can be helpful.
  3. Lower end brake components - A lot of lower end disc brake sets have variations in the pads and rotors that just naturally encourage a squeal. Sometimes as they wear it will diminish, but often you are stuck with the sound unless you want to fork out the money to upgrade.

Note that especially in case 2 and 3 you will see the behavior you describe where the squeal is worse when the brakes are applied lightly. As you apply more force you remove the ability of the involved parts to vibrate.

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As always, check with you local trusted bike shop...

But, is there any issues with the brake pad and disc? In other words, assuming no trapped grit, is either warped in ay way, has a burr, etc.

If it's been happening since day one my guess would be some minor maladjustment in shape of the brake pad or disc. Or just the mix of materials causes squeaking.

But again check with your local bike shop mechanic to see if they have any ideas.

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in addition there is - bicycling.com/maintenance/repair-maintenance/… - and another site I read suggested making sure the pads and rotor are clean. –  edgaralgernon Aug 10 '11 at 13:53

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