Nothing wrong with BB7's;they're the standard in cable discs. I currently own 6 bikes equipped with them,and have previously owned 4 others.
destikon: here's the link to Avid's manuals.
http://www.sram.com/en/service/avid/...D=1&subcatID=1
I'd suggest reading over this and see if it fixes your problem. The first time I ever messed with BB7's was when I installed one on the front of my Surly. I just followed the instructions and it worked perfectly. I had issues with my Dixon's front BB7 not stopping,and it turned out to be improper installation. The caliper was mounted at a slight angle(the washers were in a different order between the two mounts). Take a look down into the opening of your caliper and see if the rotor is straight and parrallel between the pads. If not,the caliper may be crooked like mine. It could also be that your rotor is warped. I had this problem on one of my bikes when it was new from the shop. It had gotten banged during shipping or essembly and they didn't catch it.
To date,every single problem I've had with any of my disc brakes(all models/bikes) has been from improper setup by the shop,damage during shipping,or playing bike polo(which doesn't count cause that's really just abuse).