Cantilever Brake Installation (can thick and thin cup washers be swapped?)

Question

I'm reinstalling the rear cantilever brakes after taking them off for a thorough cleaning. I'm also upgrading the pads at the same time to a Kool Stop model with "extra material" (i.e. thicker than standard pads).

I'm having a lot of trouble getting the pads to sit at what I think is the ideal position where when they contact the rim, they're flat against it in the vertical plane, with a slight toe-in, and with the top edge of the pad hitting just below the top edge of the rim.

Right now this is about the best I've been able to do:

As you can see the bottom edge of the pad is contacting the rim way before the top edge.

I'm not sure of the model of brake, but they came stock on a 2010 Specialized Tricross, and are the kind where the brake shoe has a threaded bolt out the back that passed through the brake arm with a set of rounded washers on either side that allow you a lot of freedom in pad positioning.

I'm finding that if I loosen the bolt and manually position the brake pad exactly how I want it to hit the rim, and push the brake arm in so they're both in the right position for initial contact, I can get it just right. So the cup washers and other components have the degree of mobility required to position it right.

But getting the pad positioned right requires the bolt to pass through the brake arm almost as high up as it can go, i.e. something like the yellow line here...

... and no matter how hard I try to hold everything in place while tightening the bolt, it inevitably shuffles back to a position where the bolt is closer to normal to the face of the brake lever arm it passes through. Which has the effect of tipping the pad up slightly into the position shown above.

It feels like part of the problem is the extra pad thickness is making the pad contact the rim earlier than maybe the frame and brake geometry is ideally suited for.

So I've got two questions:

1. Is there something fundamental I'm missing here?
2. Is it OK to swap the inner and outer cup washers? The inner one is much thicker than the outer one, so doing that would move the pad straight back towards the brake arm by a couple of mm I think. I.e. can I do this: I think doing that would allow me to get the right initial pad/rim contact position with the bolt much lower in the brake arm and therefore easier to control as it's tightened.

Answer 1

Yes, you can swap the thin and thick washers, in pairs.

That means you do still need to keep a cup and a cone washer together. That is, a convex and a concave washer, and there still has to be a pair on either side of the canti brake arm.

Also, best practice is to have the convex washers both backing onto the brake arm, and the concave washer backing onto the pad and onto the nut. This gives effectively a "hamburger" shape with the canti's brake arm in the middle.
Why? This allows for the whole thing to be clamped down at an angle where required, and to hold that angle.

I tend to throw old brake pad mounting hardware in a jar and keep it. That means nuts and washers of all sorts. I did have to fit thin washers on both sides because a bike had extra thick brake arms, and the new pad stems were shorter than the old worn brake pad stems.

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Looking at your middle photo, it may help to file the very bottom of the bolt-slot. Inspect closely and decide if there's enough thickness of metal to do this safely, but extending that slot even a millimetre will help reduce the angles. Added bonus is more mechanical advantage to your braking as well.

Good luck!

Answer 2

Yes, those washers are intended for swapping.

The reason they're there is because of cantilever brakes having a variable mechanical advantage that depends on the exact frame / fork where you install the brakes. So if you find the mechanical advantage too low or too high, you must adjust it.

The mechanical advantage of cantilever brakes is adjusted by:

• Link wire / straddle cable length: if you have straddle cable, you can adjust its length manually, link wire has a fixed length so you need to swap it to another length of link wire (multiple lengths are available from brake manufacturers)
• How far the pads extend from the brake arms

Usually you do fine mechanical advantage adjustments (small adjustments) by adjusting how far the pads extend from brake arms, and coarse mechanical advantage adjustments (large adjustments) by changing link wire / straddle cable length.

Some old cantilever brakes have a smooth post and you can slide the post freely on the brake arms. Newer brakes usually have a threaded post, and you adjust it by swapping the washers from one side to another. Usually there are multiple washers, some thin, some thick. The two cup washers are usually of different thicknesses so you can swap them from one side of the threaded post to another.