400E

Hello,
I have Avid BB7 disc brakes on my Surly Disc Trucker. About a year ago I replaced the stock rear pads with genuine Avid sintered metal pads. I'm generally satisfied with them.

A couple weeks ago I realigned the caliper and everything seemed fine. For some reason after this, every few rides I notice that the brake lever travel is less than at the last ride -- in other words, the pads are closer to the rotor than I had initially adjusted them to be, and the pads are now rubbing on the rotor when I spin the wheel. If I back off the adjusting knobs a few clicks (inside twice as many as the outboard one), everything's fine again until next ride.

I can't figure out how this happens. Has anyone seen this?
thanks
Steve

JanMM

I've used BB7s since 2003 and haven't experienced what you describe. Wheel securely in dropouts? Brake caliper securely in place after you adjusted it? Brake lever cable adjustment - if any - secure? Pads not worn down? Tried realigning again? Housing/cable in good shape?

400E

Thanks -- great things to check out. Today for whatever reason the symptom didn't show up -- brake lever travel exactly as I left it yesterday. I will check out these ideas this weekend.

operator

Cable isn't slipping in the anchor, or breaking is it?

Check close to the head of the cable and inspect length of cable. Especially if it hasn't been replaced in a while.

400E

Does not seem to be slipping. Cable looks fine, anchor bolt tight. No barrel adjuster.

Re-centered wheel in the dropouts, made sure all bolts are tight. I readjusted (i.e. loosened) the 2 adjusting knobs again today and will see how it goes.

400E

Well, the sintered metal pads seem to lose their friction (i.e. seemed contaminated) so took them out over the weekend, cleaned them with auto brake cleaner spray, and put them back and realigned the caliper. Fine for the first couple rides and now again had somehow gotten tight enough that the pads were rubbing tonight for my ride. I backed off the adjusters again.

This remains a puzzle to me. The only thing I can figure is that the pads themselves are the culprit. I did not have this problem with the original organic pads that came with the bike. I am wondering if somehow I got a bad set of Avid sintered metal pads somehow, that swell up with use? Not sure if this makes sense, but I really can't see another way for this to happen. The cable and housing is fine.

JanMM

Sounds puzzling, indeed.

400E

Over the weekend I ended up getting a brand new set of Avid organic pads -- I wanted organic anyway and thought a new set of pads might do the trick. Did fine yesterday but today the brakes gradually tightened up on my ride to the point that I had to pull over and loosen the two adjusters. At that point, the wheel was basically locked up by the pads.

I will need to pull the pads again and make sure they are properly seated, but I was pretty sure they got seated well when I installed them. They clicked into place in a satisfying way (though I do find putting in BB7 pads to be a bit fiddly, as the British say -- I have trouble keeping the pad/spring sandwich together while getting the whole assembly into the caliper).

Really annoying and strange.

headasunder

Put a pen mark on the adjusting wheels to see if they are moving?,you may have to dis assemble them to see what's going on

tFUnK

Friction somewhere in the system causing the pads to not return to open position? From the lever down to the caliper? Maybe try new cables/housing, making sure that housing ends don't have jagged parts impeding cable movement.

400E

Good thoughts. I have wondered about the adjusting wheels turning on their own somehow.
The brake lever seems to spring back normally, but the free play before the brake engages gets less (as if I had turned the adjusting wheels clockwise).

400E

Give that poster a cigar!
I put a Sharpie mark on the top of both adjusting wheels prior to my standard 10 mile ride tonight. Sure enough, the small outboard wheel is now 90 degrees clockwise from where it was at the start of the ride! Inboard wheel looks to be in the same spot.

Yes, now will have to disassemble this weekend.

Thanks for the tip!