I'm trying to track down a dragging sound from some Avid BB-7 brakes on a Kona Sutra. The hub is a Shimano Alfine DH-S501 dynamo hub with an SM-RT82 Centerlock disc. The noise sounds like a dragging pad, but, so far, I've been unable to make it go away. Here's what I've done so far:
Trued the rotor – runout is < 0.05 mm measured using a dial indicator on the rotor in a truing stand.
Aligned caliper to the rotor by loosening the caliper mounting bolts, then tightening the adjusters to clamp the rotor between the pads, and finally retorting the mounting bolts.
Checked pad thickness (wear limit), the pads are tapered, the thickness is about 3.6 mm at the outside of the rotor and about 4.0 mm at the inside.
Checked the hub bearings – the disc side locknut was loose, but the cones seem to be well adjusted. In the truing stand I can cause about 0.1 mm of deflection at the disc with lateral pressure at the rim. That doesn't seem excessive…
As I was looking at the brakes, I noticed that the pads seem to be closer to the rotor at the outside (like their resting configuration is 'V' shaped). As I adjust the pads I start to hear dragging sounds well before the brake travel is reasonable (the lever will go all the way to the bars, and I can move the wheel by hand when the lever is bottomed out). There seems to be a reasonable (i.e., way more than the runout in the disc) amount of space between the pads and the disc where I can see.
I also noticed that the pads themselves do not sit parallel in the caliper. With the adjusters backed all the way out, I can get one side or the other to sit against the frame of the caliper, but the other is slightly angled. It seems like the spring is not pushing out evenly.
Any ideas about what I should do next? Should the pads be tapered / sit in a 'V'?