[metalhead119042]

Hello, I recently bought a pair of Avid BB7 mechanical disc brakes. I'm positive i have them set up correctly and the back brake works perfectly. The front brake seems to have almost no effect at all. I bought these about 2 weeks ago and have ridden the bike pretty much every other day. I really hope sanding the rotor wasn't damaging it because me and my dad thought it would help roughen it up and little and make the pads grab better.

 

[sanjuro]

1. The outboard pad should be almost touching the rotor, and the inboard pad (which is the side that actually moves when you squeeze the lever) should be about .5mm away from the rotor.

2. The rotor might be possibly warped, even thought it is new. This would diminish braking power.

3. Finally, you might check your cable housing. If it is split anywhere, particularily at the ends, it will dramatically affect your power.

 

[metalhead119042]

Well to answer one by one:
1. The pads might be slightly off of what you said but they are very close to the rotor.

2. When I ride the bike i can't see any bend in the rotor anywhere.

3. The cable housing and cables are brand new so i'd be surprised if something was wrong with them.

Would you think sanding the pads would work? To wear down the pad a little more and try to get the top layer off.

 

[sanjuro]

Well to answer one by one:
1. The pads might be slightly off of what you said but they are very close to the rotor.

2. When I ride the bike i can't see any bend in the rotor anywhere.

3. The cable housing and cables are brand new so i'd be surprised if something was wrong with them.

Would you think sanding the pads would work? To wear down the pad a little more and try to get the top layer off.

1. Being very close is not correct. Unlike hydraulic brakes, which both pads push against the rotor, the Avid mechanicals are single-sided-actuated. The outboard pad should be almost touching, or braking power will diminish significantly. If it is not almost touching, when the inboard pad pushes against the rotor, the rotor will not make contact the other pad.

By having the outboard almost touching, both pads make contact when the inboard pad actuates.

2. The only way to check rotor warp to watch the rotor as it goes the brake, and to carefully watch if it makes contact with any of the pads (or to use a micrometer on a truing stand). You cannot notice rotor warp when riding, but being less than a foot from the brake (typically when the bike is upside down or in a workstand).

3. I would not assume your housing has not frayed or split because it is new. Many times housing splits because of improper installation.

If the first two steps reveal nothing, I would undo the cable, and pull off the housing ferrules and confirm no splits or frays.

My final comment is that a thorough mechanic checks the little things first and makes sure they are not problem before assuming something worse...

 

[metalhead119042]

Well i moved the outboard pad so it is extremely close and that helped just a little bit. When i have more time later i'll check the cable.

 

[Munster]

Maybe there is slack in the cable? Try taking it up with the barrel adjuster at the lever, just enough so that the torque arm on the caliper is about to be pulled.

 

[burly50]

I recently got a new bike w/ BB7's. My first experience with disk brakes. When I rode it the first few times I was extremely dissapointed in their performance. LBS told me to keep using them, they (the pads) take a while to break in. I actually thought that some thing was wrong with them. Then, all of a sudden on my next ride, I went over the bars on a not so steep down hill section. LBS was right. Needless to say, I learned to modulate.
Give it time, and ride a lot. They should be just about ready to start working properly. If they don't, some thing is wrong. Most likely in the set up.

 

[urbaindk]

Sanjuro, regarding your number 1 comment.

I set mine up differently. When setting the alignment I tighten both pads, watching carefully to make sure I don't deflect the rotor, and then tighten the CPS hardware. After I do the alignment, I turn the outboard (moving) pad 1 click to every 2 clicks of the inboard (stationary) pad until the wheel turns freely. If I understood your description correctly you do the opposite.

The net effect of this set up is that moving pad comes in contact with the rotor first and then deflects the rotor towards the stationary pad. If done properly this will give you terrific modulation. As long as you don't add too many 'clicks' you should have plenty of stopping power. I usually try to set them up so that they are fully locked at one knuckle thickness to the bars.

And like Munster said make sure that the cable is as tight as you can get it with out actually pulling on the caliper. I personally don't do this with the barrel adjust. I find it easier to loosen the cable stop and then pull the cable end with a pair of pliers so that I pull all the slack out of the cable all the way to the lever. Then I tighten the stop back up. Do it carefully and you won't put any load on the caliper.

I've tried it the way you described Sanjuro and I felt the brakes were too grabby or on/off for my tastes.

 

[BikeGeek]

1. The outboard pad should be almost touching the rotor...

Yup, the manual suggests the ideal ratio of offset to the outboard side is 1/3 to 2/3.

...and the inboard pad (which is the side that actually moves when you squeeze the lever)...

It's the outboard pad that moves, pushing the rotor into the stationary inboard pad.

 

[metalhead119042]

Well they finally started working better, guess it just need some more fine-tuning and wearing in. Thanks for the help!

 

[BIRDMAN111]

yeah they probably just needed a good ride to break in. i know when i got new pads they sucked at the beginning of the ridel, and with enough good, hard stops they broke in.