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I have bought an old mtb with cantilever brakes. Front has regular yoke and works just fine. Problem is in the rear, where there's a Power Hanger bolted into the frame just above the tire. It looks like that: enter image description here

only not on the fork.

Brakes are very soft, movement of pads is uneven, they are unable to lock the wheel no matter what.

I'm wondering if this hanger is properly mounted, should it move while braking or should it be bolted tight?

I can't imagine how this device would work. I already found that it's based on a bell crank but I can't see how it applies to braking. How, physically, would movement of one arm cause the other to get closer to the rim?

  • I've never seen that design before. You could probably fit conventional V brakes without an issue. – Criggie Mar 14 '19 at 6:01
  • @Criggie I took me lots of time to even find what's that solution called. With that knowledge it was still impossible to find any information on setup, maintenance. Nothing. I'd like to keep brakes as bike is very old and I'd like to keep it fully original. This strange contraption will be on the plus side of bike ( if I manage to make it brake ofc :) ) – zubergu Mar 14 '19 at 8:28
  • Fair enough - consider replacing the brake pads if they're not known to be new/recent. Even good looking ones can be hardened with age. – Criggie Mar 14 '19 at 10:54
  • @zubergu brakes are kinda important. You could bag the old ones and store them for future need, but stopping on demand is preferable. Admittedly these are back brakes which are under 10% of your braking capacity, BUT if the front failed in service AND these were in place you could be left with almost zero braking ability. I'd fit either V brakes or some kind of hanger from the seatbolt to mount the cantis normally. – Criggie Mar 14 '19 at 11:02
  • Is this configuration the original design (which I doubt) or was it added by the previous owner and for what reason? – Carel Mar 14 '19 at 12:27
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It needs to be bolted tight to remain attached, but the hanger is mounted on a collar so is always free to rotate as it’s designed to.

So yes to both, when it is bolted tight it is still free to rotate.

Normally a brake housing fits into rigid frame stops. These stops resist the force of the outer cable so all the cable force pulls on the brake where the inner cable is clamped. In this case, because the power hanger can rotate, when the cable contracts, the right brake arm moves as normal but the power hanger moves too (clockwise). This pulls on the secondary cable attached to the left brake arm, so both pads move towards the rim.

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    Thank you, that's all I needed to start working on them. – zubergu Mar 13 '19 at 21:43
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    What a strange design. It seems to rely on having enough movement in the cable housing that the force is reasonably evenly shared between the two sides. That seems to be a silly constraint and worth checking – Chris H Mar 15 '19 at 8:20
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    @ChrisH Then again, V-brakes also rely on housing mobility to move both sides of the brake. The real question is, with how much force can one side of the brake polish the rim when it doesn't retract properly due to friction. I guess, this design should work fine if it's properly lubed. – cmaster - reinstate monica Mar 15 '19 at 21:43

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