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I have a very puzzling problem with the front mechanical disc brakes on a big-box retailer mountain bike. Nothing fancy, and it used to work well for over a year but since I last dismantled it to clean it and eliminate squeal it's never quite worked properly.

Problem seems to be too much lever travel; when pulled tight I can get effective braking but released fully the brakes still stick. Letting out a bit more cable from the clamp will allow the wheel to spin freely on release but the brakes are almost useless even at max.

I've tried tightening and loosening the bolt in the caliper center but this doesn't seem to change anything (what does it do anyway?). Can someone advise how I can reduce the "range" of mechanical disk brakes or otherwise resolve this issue?

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  • Are you sure that is not a cable problem? Does the cable snaps from the lever when you release it? If this occurs, it may suggest that the cable is stuck somewhere in the system (housings, lever, brake).
    – gstorto
    Commented Nov 12, 2016 at 20:55
  • The cable appears to be intact along its entire length. The lever connection is fine too. Any pull on the lever is directly transferred to the other end.
    – user3227564
    Commented Nov 12, 2016 at 21:17
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    Can you please add a couple of photos of the brake to your question. Ideally a side-on one and a vioew of the brake pads sitting next to the rotor, showing the gaps between them.
    – Móż
    Commented Nov 12, 2016 at 22:06
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    Are you positive the wheel is installed correctly?
    – Criggie ♦
    Commented Nov 12, 2016 at 22:52
  • Pretty sure it is, I still ride it with the rear brakes functioning sometimes up to 20mph on downhills. I'm away from home for the next 24 hours but will get the requested pics posted asap.
    – user3227564
    Commented Nov 12, 2016 at 23:15

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Mechanical disks almost always operate one side only. Setting them up correctly is not hard but needs care.

Refer http://www.parktool.com/blog/repair-help/avid-mechanical-disc-adjustment#article-section-3 for detailed instructions for Avids - technique should work for other brands.

Essentially, slack of the cable and caliper mounting bolts, Undo both pads (counter clockwise) then tighten the outer pad 1/2 turn. Tighten the inner (non-cable side pad) until the disk is clamped tight and then tighten caliper bolts to set the caliper. Tighten the cable, loosen the inner pad 1/2 turn and outer 1/4 turn, then adjust as needed for modulation.

Although this sounds difficult and long winded, its actually only takes a few minutes once you get used to it.

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