Adjusting cantilever brakes

stevie_b

Senior Member
Location
Hampshire
My mountain bike's got traditional Deore LX cantilever brakes with a link wire. Due to normal wear of the brake blocks I was finding that when I squeezed the rear brake lever so that it reached the handlebar, the blocks were only just touching the rim.

To fix this I moved the brake shoes along the axis of their posts so that they sit closer to the rim in their relaxed position. This cured the original problem: I only have to pull the lever a bit for the blocks to make contact with the rim.... but although the brakes feel nice and firm with the bike stationary, they don't inspire confidence when moving. I have to squeeze hard to get any effect, and then they're likely to just lock up the wheel.

Reading Sheldon Brown, it sounds like I don't have enough mechanical advantage in my rear brakes:
http://www.sheldonbrown.com/canti-trad.html

I'm trying to understand what's going on. Could moving the brakes along their posts cause a decrease in MA?

Sheldon Brown suggests lowering the cable yoke to increase the MA. What's the best way of lowering the yoke? Do I have to thread more cable all the way from the brake lever so that there's more cable at the wheel end, hence the yoke hangs lower?
 

plantfit

Guru
Location
Lincolnshire
Hi Steve,

Perhaps it would be better to shorten the inner brake cable a bit to adjust lever travel, by moving the blocks along the posts you might have altered the amount of block that touches the rim,try to set the brakes up so that all of the pad profile touches the rim square on when the brake is applied and the bike is in a forward motion, don't forget to do this when the bike is stationary you will need a small amount of "toe in" on the brake pad, ie: the front of the pad touches the rim of the wheel before the rear of the pad if you know what I mean.
good luck

Roger
 

battered

Guru
At a guess you have indeed changed the MA of the brake. If you think of the mechanics of what is happening, you can have a man suspended by a rope and the only force required is his weight. The same man on a tightrope exerts a massive force on the anchors. This can be expressed in vectors if you are mechanically minded, engineers do these calcs all the time.

V brakes get round this by ensuring that all the cable force pushes the brakes on the rim. For cantis you have to set them up so that the force acts in as straight a line as possible on the actuator. If you are puling at an angle you are losing efficiency, think of our man on the tightrope again. HTH.:biggrin:

Oh, and the other suggestion about getting the pads in full contact is goodadvice too, get the basics right first. You may also have introduced more flex by poking out the pads, this won't help as brake forces are heavy at the best of times.
 
OP
S

stevie_b

Senior Member
Location
Hampshire
plantfit said:
Perhaps it would be better to shorten the inner brake cable a bit to adjust lever travel
How do I do this? Is this an adjustment to be made at the brake lever?

I think the pads are making good square contact with the rim (allowing for a very small amount of toe-in).
 

RedBike

New Member
Location
Beside the road
Cantis are a pain in the backside to adjust.

Once you've got them set right don't touch the straddle wire or the pad holders, this will only mess things up. Instead you adjust the cable at the brake lever or via an inline adjuster at one of the hanger.
 
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