disc brake problem
 

Raliegh xxix, avid bb5

My rear brake acts normal. No squeaking, smooth braking. But something is wrong with the front.

Even when the stationary pad is backed way out, the still brake squeaks. Before it would only squeak when where was no weight on the bike, now it squeaks all the time. The main problem is that it doesnt brake smoothly or consistently, it sort of chatters... pulls hard and lets up really fast under moderate braking.


Any idea what the problem is, or what needs to be adjusted?

Would I be best off just upgrading the front brake?

My first guess would be to check that every bolt is torqued down and that you haven't somehow lost the spreader spring.

I'm guessing that the cheapest thing you can try is replacing the front disc pad. The existing pad may have a defect or may have something embedded in it. Also make sure the disc is clean. I have BB7's and occasionally get a squeal but they have been a great improvement over the v-brakes I used before which squealed a lot.

I tightened everything up and that didnt seem to help so I cleaned the disc and pad with a solvent. (not sure if that was a good idea?)

Now the brake dosent squeak, and operates very smoothly. The only problem is the braking power really sucks now. I hope I didnt damage the pad, maybe it just need to dry out for a while?


also, the spreader spring is fine.

Hydraulic disc are not my area of expertise, but I do know this about cable disc...

One pad (the static pad) should be just touching the disc, giving a very slight scraping noise as the wheel turns, the other pad should be set as close as possible without touching the disc.

Now okay, it could be the system on your bike is different, both pads may move inwards, I have no idea, as I say I know more about cable disc brakes. But it is something to check?

I disagree.

If the rotor is true there should be no rubbing on a properly set up brake, and no power loss. I understand putting up with a little rubbing if you have no provisions for truing the rotor, but if it is true, the rotor should be set a gnat's hair from the inside pad, not touching it.

I'd check the caliper alignment. It can be very hard to see if the caliper is not perfectly parallel to the rotor. A good test is to watch how the rotor deflects from above. If one side flexes before the other, make the appropriate adjustment for either plane.

Depending on the mounting type, the tabs may not allow a full range of adjustment for the BB5's domed washers. You can move the caliper inward by adding thin washers (the type from old nutted brake shoes work well) to the bolts that hold the adapter to the frame or file out the top mounting holes to move it outward. Of course, use discretion when modifying and only remove what is necessary.

Bad news: Depending on what solvent you used, you may have contaminated the pads. I only use denatured alcohol to flush calipers, whether cable or hydraulic. It won't harm a thing and dries in a flash.