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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'?

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    Have you checked your wheel bearings for play? BB7 calipers only move one pad, so the fixed pad needs to be very close to the rotor. – Emyr Aug 18 '15 at 14:51
  • Thanks, I'll double check. The front hub is a Shimano Alfine dynamo, I'd assumed (I know, I know) that it had sealed bearings like the SON. But thanks to your comment I just discovered that it does not. I'm going to add the hub type to the question. – dlu Aug 18 '15 at 15:32
  • Checked the bearings. The bearings themselves seem to be well adjusted (or too tight, I'm not sure how to distinguish between the "notchiness" of the generator and that of overly tight bearings), but the disc side locknut was quite loose. – dlu Aug 18 '15 at 16:56
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To align the caliper, loosen the caliper bolts and bring the fixed cpad as close as possible to the rotor without rubbing. Then dial in the fixed pad so that it is as close as possible without rubbing. Then install your cable/housing, and begin adjusting.

To improve brake feel, pre-stretch your cable before making adjustments. Take the wheel out, out a pad spacer in (Pedro's tire lever works great, or any other non-metal object), and squeeze the lever as hard as you can ten times. This will seat the housing into the ferrules, as well as stretch the cable out.

If the pads are sitting in a "V", then the brake pad spring most likely needs replacing. You could also try spreading it open a bit first, but the springs are so cheap that it's worth it just to get new ones.

P.S. The Alfine dynamo actually uses loose ball bearings, making it re-packable. It's tricky, due to the wiring connectors, but it's nice to be able to do it yourself.

Avid Brake Pad Spring

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