Disk Brake Question

[twilkins9076]

We've had our first tandem for about a month now, and there is something about the rear Avid disk brake that I can't figure out. Our stopping power seems very adequate, but the STI brake lever has so much travel that it bottoms out on the bar. There is no barrel adjuster on the cable, and I've tightened the cable at the rear to the point where it is just beginning to put pressure on the brake shoe, but I still bottom out on the STI lever.

Is this normal, or is there some other adjustment that I'm not seeing?

[bolton2160]

Are your pads adjusted correctly? Was this a problem from the begining when you bought the bike?

[twilkins9076]

The pads seem to be adjusted correctly. I've checked the SRAM web site for that, and they match the diagrams posted out there.

I didn't notice them bottoming out the first couple of rides, but I was pretty pre-occupied with the "newbie tandem" syndrome, and they could have been. At first, I thought it was just cable stretch associated with the new bike, but after taking out the little bit of slack there was, the brifters still bottom out if I mash on them hard.

As I said before, the disc stops us just fine, and this is my first experience with a disc brake, so I'm not sure whether I should be concerned or not.

[bolton2160]

I guess if your stopping ok then there's no concern. I just put the Avids on my mountain tandem and had to play around quite a bit with the inboard and outboard pad adjustment to get the feel just right. If I mash on mine hard, the lever will bottom out but the disk has locked up before that.

[Retro Grouch]

We've had our first tandem for about a month now, and there is something about the rear Avid disk brake that I can't figure out. Our stopping power seems very adequate, but the STI brake lever has so much travel that it bottoms out on the bar. There is no barrel adjuster on the cable, and I've tightened the cable at the rear to the point where it is just beginning to put pressure on the brake shoe, but I still bottom out on the STI lever.

Is this normal, or is there some other adjustment that I'm not seeing?

The guys that I know who use Avid mechanical rear brakes also use an in-line travel agent to get a little more cable pull.

[Old Hammer Boy]

We have BB-7s on our tandem. Once you get the cable adjusted, there should be no reason to adjust it very often. If I have the pads correctly adjusted, my levers (Ultegra brifters) don't come close to bottoming out. Here's how I adjust them: I spin the wheel and adjust the internal red knob until the pad starts to drag against the rotor. Then I back it off 2-3 clicks. Then I do the same for the outside pad. Just be sure that the inner pad is showing about 2/3 while the outer pad shows 1/3 of pad material. The reason for this is because you don't want to deflect the rotor too much. If you don't see that (approximate) ratio, you'll have to loosen the brake mounting bolts, and reposition the calipers. Avid directions detail this procedure. Good luck... OHB

[K&M]

We had quite a few struggles with the same problem when we got our Avid rear disc equipped tandem. Bringing the brake pads in tight enough to keep the lever from hitting the bar puts them extremely close to the disc. With the slightest warp in your disc or wobble in your hub, you will be rubbing. This also means that even the slightest wear on the brake pads will result in the lever crashing into the bar again. We do long rides with lots of brake intensive descending (long, steep mountain grades with constant hard turns) and we were having to stop during rides to dial the pads in closer in order to keep the lever off the bar. Others who ride in similar conditions have added travel agents, so we tried that and it seemed to help (although people who probably have a much better understanding of mechanical engineering than I, have argued on this forum that it's impossible for travel agents to provide a benefit here). Others have found the brakes don't retract as quickly as they'd like and have added a spring (extensively discussed in previous threads). We haven't had that problem, so haven't tried that.

In the end, the thing that has helped the most is me simply making peace with the fact that, like it or not, the rotors are going to squeek against the pads once in awhile while we're riding. Once you decide that occasional brake rub isn't the end of the world, you are free to dial the pads a click or two further in and the problem is pretty much solved.

[Map tester]

I use the procedure from the Park Tools website:

AVID® MECHANICAL DISC ADJUSTMENT (http://www.parktool.com/repair/readhowto.asp?id=124)

[K&M]

Looking at the Park Tools procedure for installing the brakes reminds me. To get a correct alignment we also had to add a couple of washers to the mounting bolts.

[dfcas]

Are you sure you have the "road" version and not the "mountain" version caliper? The cable pull is different on them,as trhe road version has a shorter "arm" that the cable attaches to.My Campy levers have plenty of cable pull for ours.

dan