Nucks

Hi,

So, for some reason the arms of my rear cantilever brakes (shimano, early 1990s) do not sit evenly at rest. What I mean is when the cable is disconnected, the left arm (looking from rear) is quite far from the rim compared to the right arm. The right arm has a tension screw but that doesn't seem to affect anything. When I was looking them over I noticed that the spring on the right arm was in a different hole than the left arm. Everything I've read says they should be in the same hole and so I changed them so now the spring goes through the middle hole on each side. I'm not sure if that changed anything or not. Anyway, all I can think of is that I need a shorter link cable so it will pull the left arm closer to the rim. The left arm is the one that is on the link cable side. It is an "A" link cable which I believe means it is 73mm long.

In any case, I put it back to together and tried aligning the pads properly but given that the left arm starts so far from the rim I had to push the pad out quite far on its post to reach the rim. The pad on the other side is right up against the brake arm which seems ideal because it isn't hanging out on its post as much which seems stronger, more stable.

If I do need a shorter link cable that is weird because it is original equipment so should be the proper length.

Is there perhaps damage to the spring on the left side so it isn't holding the arm close enough to the rim? Anyway, these things are a mystery to me.

As I said, when the arms are unattached from any cable the left arm is naturally quite a bit further from the rim than the right arm.

Any gurus have ideas on this?

I suppose because the type of center pull cantilevers are not as common today the web resources I've found have not been helpful for this problem.

striknein

A difference in spring tension between the two arms is the most likely culprit. I would first back the tension screw out all the way. I'd then try to increase spring tension on both sides by placing the spring arm through the top hole of the braze-on. Then readjust the tension screw until the brakes are properly centered. Be careful not to over tighten the brake mounting bolt; doing so could mushroom the mounting post and cause the brake arms to stick or bind up.

I've "adjusted" spring tension by bending the spring in the past. It's a fiddly, time consuming process. Next time, I'll just throw the brakes away and buy a set of ct91 arms for 20 bucks.

if you're using a shimano link wire, you should also make sure that the cable runs parallel to the line on the link wire's sticker.

FBinNY 

Yes the springs aren't perfectly matched. But it doesn't matter.

The system needs to be balanced in the open position with the cable attached. As long as that's possible with the small balancing screw, nothing else matters.

Welcome to the world of made to work, not to be perfect.

Nucks

I don't think it is possible to balance it with the small balancing screw. And there is only one on the right arm. I screwed it all the way in and all the way out and didn't notice any difference but I'll try again and see if there is something else going on.

Ive got the link cable attached correctly but it just seems that shorter link cable would solve my problem but like i said it is original equipment.

corrado33

If there truly IS a difference in spring tension, a shorter link cable will not help, it'll just pull the closer arm into the the rim. The springs don't ALWAYS have to be in the same hole. On older bikes, I've often changed the hole of one of the springs in order to match the tension between the arms. In order to see an affect of the tension screw, you need to squeeze and release the brakes. Screwing it in and out you'll notice that that side (the right side in your case) will "stop" (after you've released the brake lever) further or closer to the rim depending on whether you're screwing in or out respectively.

What I would do in your case, if it is the left arm that's further from the rim, I'd take that spring and move it down (to the less tension position), or take the right arm and move the spring up to the higher tension position. Then use the adjustment screw to balance the brakes so that they don't drag on the rim when you've released the lever. Remember you need to squeeze and release the brake lever in order to see the effect of the adjustment screw.

There is literally only 4 adjustments on those brakes. The position of each of the springs in the braze ons, the adjustment screw, and the length of wire between the brakes. Play around with it until it works. It doesn't need to be perfect. You don't NEED to replace anything unless it's actually broken/frayed. That's the nice thing about cantilever brakes. You can almost ALWAYS get them to WORK.

exmechanic89

I've found bending the springs - that is increasing the tension on one side or the other usually works best. Easy to do and can be done fairly quickly. That said though I can never get my cantis to ride as perfectly as I used to do my road brakes. They can be damn annoying sometimes, lol.

cny-bikeman

Corrado's solution is appropriate - first position the springs in the holes so as to make the tension at the rim as close as possible. Then you can use the adjustment screw for final tweaking.

Nucks

OK. That might explain why they were in different holes in the first place. It must come down to a difference in wear or something between the left and right springs. Maybe two new springs is the answer. Anyway, i'll try using different holes in the brazeons to adjust tension first. Thanks for your answer!

fietsbob

the cable hangers for transverse wire , some have a Setscrew to put it off center , then tighten the screw against the cable.

over winding and back winding the caliper bends the spring a bit* and the brake shoe post length is another adjustment

this is simple to do with plain post types ,or a few washer swaps on the V brake type shoe mounting scheme.

I bend a curve in the straight V brake springs , if the little adjustment screw is inadequate in that task.