Wonky cantilever brakes

[lulubel]

This is frustrating me because I know it isn't right (even though the brakes work) so hopefully someone will be able to tell me how to sort it.

I have canti brakes on my new bike. They were an absolute pig to set up and get working properly, but they are working, so I'm quite pleased with myself. The problem I have is that the "hangar" part (don't know if that's the correct word for it) that the main brake cable connects to isn't centred over the wheel, and the main brake cable is going off to one side rather than being vertical. The cable that runs through the "hangar", connecting the 2 brakes, is longer one side than the other, but the brake pads are an equal distance from the wheel rims. If I adjust it so that both sides of the cable are the same length, and the "hangar" is centred, one brake moves away from the wheel and the other rubs.

Hopefully this makes sense and someone can tell me what to do about it because I'm sure it shouldn't be like this and it's really frustrating me. As I said, the brakes work, but they only work if the cable is going off to one side.

 

[Scilly Suffolk]

Not entirely sure that I follow (photos would help), but I always find the Park Tools blog useful.

 

[Herzog]

When you first put the brakes onto the brake mounting bosses, were there different options of how close you could position them to the wheel rim (i.e., 3 small holes in the fork next to the bosses)?

 

[mcshroom]

I'm thinking this is a straddle cable issue. It could be that the straddle cable is too long/short.

In general thares some decent stuff on Sheldon Brown's site - http://sheldonbrown.com/canti-trad.html

 

[lulubel]

When you first put the brakes onto the brake mounting bosses, were there different options of how close you could position them to the wheel rim (i.e., 3 small holes in the fork next to the bosses)?

Yes. I've got Zinn's road bike book and also the Park Tools book, and in one of them it said to start out by positioning them in the middle holes, so that was what I did. I didn't see any explanation of why you might need to use the other holes, though, so I have wondered if moving the one that wants to be further away into the top hole would solve the problem.

 

[RecordAceFromNew]

As Mcshroom said the question is whether you have link wire rather than a triangular yoke. If link wire is it the right length?

I wouldn't change the middle hole boss position unless I could feel the sprung force being quite different between the left and right calipers when both are in the middle hole and not connected. If there is a slight spring rate difference you could usually equalise by adjustment bolt(s).

 

[mickle]

Pics please.

 

[Andy_R]

Sorry if its stating the bloomin' obvious, but what about the centering screws. Have you checked them?

 

[lulubel]

Sorry if its stating the bloomin' obvious, but what about the centering screws. Have you checked them?

What are the centering screws?

Pics please.

I can't provide pics because I don't currently have a working digital camera, or I would have done in my original post.

 

[Andy_R]

Just above where the canti arm mounts onto the frame you should find a small screw (on the arm, not the frame). Screw in to move the arm away from the wheel, screw out to move the arm in. Get both arms under the same amount of tension and you should be able to set your straddle wire centrally.

 

[Alun]

If the pads are the same distance from the rims, and the brakes are working OK, I would leave them as they are, canti brakes are a law unto themselves.

 

[lulubel]

Just above where the canti arm mounts onto the frame you should find a small screw (on the arm, not the frame). Screw in to move the arm away from the wheel, screw out to move the arm in. Get both arms under the same amount of tension and you should be able to set your straddle wire centrally.

Found it - thanks. It's so tiny, I'd never spotted it. I'll have a fiddle with that today and see if I can get it right.

 

[mickle]

Centre the straddle hanger ont straddle cable then adjust the centring screw(s) to balance the cantilever arms. Throughout the process pull good and hard on the brake lever to encourage the system to settle. And be prepared to tweak them a wee bit in the first week.

 

[lulubel]

Thanks to everyone for the advice.

My brakes are now all nicely centred and still working properly.