Avid BB5 asymmetrical pad rub position and squeal I'm setting up some Avid BB5s.

As I tried to bed in the brakes, the front one squeals quite heavily, the back does not.

The following image is of the non-drive side of the front disc rotor. (Where the outboard pad hits.)



The following image is of the drive side of the front disc rotor (where the rotor is pressed into the inboard pad.)



Notice the marks where the pad material has transferred onto the rotor in each picture. The marks end further inward toward the centre of the disk on the outboard pad side, than on the side where the inboard pad hits it.

Because of the way the brake works (bending the rotor at an angle as it is pushed into the stationary inboard pad), this would make sense to me as the very top of the rotor hits the inboard pad, and because of the angle, leaves a gap lower down. But is this how BB5s are supposed to be?

I say this because the while a similar thing is happening on the rear rotor, it is not quite as pronounced (ie, the inboard pad side seems to be hitting a smidge more square on, and does not squeal).

I have played around with different pad adjustments as well as caliper alignment. I've tried the sanding the rotor and pads trick. And it's new so nothing is contaminated and I've used alcohol on everything just to be sure. Nothing seems to make any difference either with trying to bring the position of the inboard pad lower as it makes contact, or the squealing itself.

I took it to my LBS, he seems to think it's an acceptable set up and just needs riding, but did not say why the rear seems to be acting differently to the front, despite setting them up in the same way multiple times. Could it be a slight manufacturing defect on the front one that causes the inboard pad to sit at a slight angle (it's not totally clear with the naked eye).
Having seen some mechanical disk brakes over my life, the Avid's 9 out 10 will emit some sort of sound.

You indeed are correct about how a mechanical disk brake works, by bending the rotor. So it's most important to set them properly. This is my procedure:


Take the caliper off, and check that the pads are parallel. Clean them if necessary.
Check if the rotor is tightly bolted to the hub.
Set the fine adjustment bolt on the lever and the caliper to none(all the way in)
Mount the caliper and bolt only using your hands
Bolt the cable lines.
Set, the static usually, adjustment to lock the rotor, then set it back half a turn.
Now, hold the handle with a ziptie and lock the brake.
Meanwhile use a hex tool to tight the caliper bolts
Finally, fine adjust the brake line.


Hope this will help you.