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Problem:

  • I can't mount the caliper in such a way that the wheel spins perfectly freely (There's always a slight rub).
  • When the brake engages, the rotor bends slightly (because the caliper isn't centered...)
  • I can't screw the caliper in far enough over to the outside so this doesn't happen... I'm guessing the bracket, where you mount the disc brake on the fork, was welded onto the fork at slightly the wrong position (i.e. a little bent, too close to the wheel)?

Question: Can I solve this myself? If I take it back to the bike shop where I bought the bike, what should I insist on?

I have a new, Bianche Volpe disc brake bike (it's steel). Hayes CX Expert mechnical disc brakes.

I know from the other disc brake bike I have that the standard way to center the caliper is to (1) squeeze the brake closed (which positions the caliper properly) and (2) screw the brake into the bracket on the fork in exactly that position!

But I can't do step 2! It's close, but it's off... Is there anything I can do? Take it back to the bike shop I bought it from? Should I insist on a new fork? Or can they work this out somehow?

It's not so bad that the bike doesn't work, but this can't be right...

caliper

Rotor and mounting bracket: (it looks like there's a slight angle and the bracket is a bit too clo

Rotor and mounting bracket

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  • 1
    Could you take some photos from slightly further back?
    – alex
    Commented Jul 1, 2016 at 4:37
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    Is there no trim screw for pushing the inside (nonmoving) pad toward the disc? The moving pad should not be bending the disc that much.
    – Kaz
    Commented Jul 1, 2016 at 5:51
  • @Kaz the caliper is at a slight angle... so even if you tighten the inside pad to the point of touching, there's some non-trivial rotor bend when pulling the brake lever because it forces the rotor to assume the same angle as the caliper...
    – Matthew Gunn
    Commented Jul 1, 2016 at 6:24
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    The video is broken.
    – MaplePanda
    Commented Nov 27, 2021 at 19:40
  • I fixed the video link, but it's kind of a bad video that doesn't capture what's going on. As I explain below, it turns out the braking caliper mounting surface was welded onto the steel frame at too much an angle for the Hayes disc brakes to ever work properly. Bike mechanic resurfaced the mounting bracket as a warranty job. I thank everyone though for the excellent comments! I was very much learning this stuff back then.
    – Matthew Gunn
    Commented Nov 28, 2021 at 1:32

3 Answers 3

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Your problem may be that you're misunderstanding mechanical disc brakes.

On most, only the outside pad moves, the disc is bent onto the inside pad. This means the loosen, clamp and tighten method doesn't work. You can do it by eye, or use a spacer between the inside pad and disk when you tighten it up.

Hayes install instructions are here.

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  • 1
    Yeah, only the outside pad moves. The outside pad is always lightly brushing against the rotor, and when you squeeze the brake, the outside pad moves in, pushing the rotor to the inside pad and bending the rotor. I can't mount the caliper further to the outside so this doesn't happen... Clearly, that would be a fix, but the caliper is already mounted as far over as it will go!
    – Matthew Gunn
    Commented Jul 1, 2016 at 4:43
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    If it's bent and new, take it back. The calliper should be straight, if it's not, thae something's up.
    – alex
    Commented Jul 1, 2016 at 8:05
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    My mech Avid instructions did not specify "loosen, clamp and tighten method". But I could never achieve adequate alignment until strapping the brake lever, loosen-and-tighten-ing the adjustment bolts, after which it was perfect. Obviously you are right if the manual says so. But if "loosen, clamp and tighten method" just happens to work in a particular case, maybe we can turn a blind eye.
    – Craig Hicks
    Commented Jul 3, 2016 at 1:58
  • install instructions link is broken; I think this is the new, working link: hayesbicycle.zendesk.com/hc/en-us/articles/…
    – Kay V
    Commented Nov 27, 2021 at 16:05
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Conclusion (for anyone interested)

The bike mechanic ended up taking the bike for a test ride and determined the brake caliper mounting surface on the fork was out of spec (too tilted) and resurfaced it as a warranty job. It's a steel bike and steel fork.

With the mounting surface at a proper angle, the kind of mounting instructions in the comments here worked.

He also said that the brakes don't have the adjustability of some higher end models (eg. with concave convex pieces with greater capacity to change the angle).

I imagine this isn't the common case, but I thought I'd post the ending of my story since people are still browsing across this.

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I'm looking at the Hayes manual https://hayesbicycle.zendesk.com/hc/en-us/articles/360037399353-CX-MX-Mechanical-Brake for "how to mount caliper to fork". Oddly, it doesn't seem to specify how the pad offsets should be set, so that may explain why you have ended up with the outer pad all the way out. I suggest this: Wind inner and out all the way out. Mount with adjustment bolts loose. Turn inner pad 2/16 in, outer pad 1/16 in repeatedly until wheel doesn't move (it is just braked - not too tight). Tighten the bolts. Turn inner pad 2/16 out, outer pad 1/16 out repeatedly until contact noise stops.

If it still is not well aligned (can't get rid of contact noise), compress the brake level with a strap to brake lock the wheel, then loosen the adjustment bolts and then tighten them again.

I had a lot of trouble getting used to adjusting my mechanical Avid brakes, but now it goes very smoothly. Now I just adjust the pad offset slightly once every ten hours of riding, to take out the slack.

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