Mountain Biking - Squeek / Humming Sound on Disc Brakes

Does anyone know the cause & solution to squeeky/humming sounds from disc brakes?

I have Avid mechanical disc brakes and my rear brake continues to sqeek/hum once I start riding for a period of time...even if I am not hitting the brakes. I do notice that the discs are also hot when the sounds occur.

I would appreciate any commetns or recommendations.

One of the pads is probably rubbing. Back it off a click and see if that solves the problem.

it is in the nature of discs to make some noise. just put it out of your mind, if they are not rubbing alot.

correct, disc brakes make noise from rubbing. it's not comparable (in regards to friction) to rim brakes rubbing as they components are completely diff. materials. you can try and fix it if you'd like but it's probably not worth your effort.

My solution, flip the bike over onto the saddle and bar, then spin the tire and listen for the squeel and try to stop the tire right on the the sound when it occur. This will be the disc pad sueeking on the rotor when it passes. Now make sure that the tire do not move and release the quick release. Next pull on the brakes firmly and hold the tire there and then tighten the quick release. This has generally work for me on my Avid BB7. If the squeel is still slightly there but disappear eventually from usage, then the problem will be solved. This has generally worked for me on my Avid BB7, especially since I adjust my brakes to hit sooner for my set up on my bike. A lot of time the rotors are not 100% flat when it rotates so it will be wavering a bit at some point and rub on the pad.

MY firend's bike (with disk brakes) hummed, then he re-aligned it and the sound went away.

The Brake alignment needs adjustment... I Recommend Putting the Bike on a Stand so tires are off the Ground... Then Pop the two Brake mounting screws Loose so the caliper is just free to move... SQUEEZE the brake, and while Holding the Brake Tight, Tighten the Mounting screws. This alaigns the Pad and caliper to the rotor... if its Really off alaignment, You May have to dissassemble and Reassemble The Axel to reposition The wheel in relation to the Caliper.

The Brake alignment needs adjustment... I Recommend Putting the Bike on a Stand so tires are off the Ground... Then Pop the two Brake mounting screws Loose so the caliper is just free to move... SQUEEZE the brake, and while Holding the Brake Tight, Tighten the Mounting screws. This alaigns the Pad and caliper to the rotor... if its Really off alaignment, You May have to dissassemble and Reassemble The Axel to reposition The wheel in relation to the Caliper.

yup this is the simplest method and 1 more thing check your rotor condition if to wavy should change new 1

If you do use the above method as mentioned by the other posters, then after you have done this be sure and back out the inboard ajustment screw, red dial(the side closest to the bikes wheel) a click or two. BB7's are mechanical and only the outboard side brake pad moves, and the inboard pad doesnt move, its static. There is another way to do this that is explained in the Avid maintenance instructions-

First loosen the claiper ajustment screws, so that the caliper has a small amount of movement in it.
Screw the inboard ajustment screw clockwise, until the pad is snug against the disk rotor, then screw the outboard ajuster clockwise until it bites hard against the rotor. The wheel should now be hard to move, as the pads are hard against the rotor. Now tighten the caliper ajustment screws to secure the caliper and stop the caliper moving. The final step is to slacken the red dials off, 2 or 3 clicks anti clockwise on both sides should be enough, and thats it. I would advise that you check the Avid pdf instructions for this, as it will undoubtably be easier to understand than me!

Just a quick question... who fitted the BB7's to the bike? Did they come factory fitted?

My mechanical disc brakes do exactly the same thing. Some days they are noisy, some days they are quiet. I figure its the nature of the beast and just put it out of my mind. They stop me well enough and the sound actually helps when something slower is ahead of me. I don't need to use the bell because the brakes do it for me.