Bicycle Mechanics - How to fix too much advantage on cantis?

The situation: I'm rebuilding a 1984 Schwinn Voyager from 27" to 700c; basically off with everything but frame/fork/handlebars/stem/seatpost. I'm keeping the brakes cantilever, and the idea was to keep the old non-aero (diacompe) brake levers. Props to Sheldon Brown, whose site has been a neverending resource and whose workplace sold me about half the ingredients for the project.

I got the cheap Shimano cantis - they went on fine with the new rims, although I had to dremel some extra rubber off of the backs of the front pads in order to let them clear the brake arm and meet the rim right. Cabled everything up, adjusted the pads, fine. The problem is that the brakes have too much advantage and feel very soft. The springload of the brakes isn't enough to snap the brake levers back to a neutral position (the hoods provide some friction here too, but it's an advantage problem, I think), and it's easy to bottom out the brake levers on the handlebars.

If I was using the yoke & straddle cable system that were on the old brakes, I could just adjust the length of the straddle cable to fix this issue. But this is a Shimano setup with the link wire. Is the cantilever angle less than 90 degrees? Not yeah, but HELL YEAH.

I've lubricated the cables and housings and it doesn't seem as though there's an unreasonable amount of cable friction - this wouldn't have much to do with the too much advantage problem anyway. I tried to avoid routing the cables in an unneccessarily bogus fashion.

So what are my options here?

* a different link wire length?

* going back to the yoke & straddle hardware? Maybe with the uberwide yoke or some such?

* Just spending the $40 on some aero levers? I'm gonna hafta re-wrap the handlebars anyway since I jacked it up the first time and from the looks of things going aero won't make the cable routing any worse. But I reckon the aero levers will lead to the same advantage issues.

Maybe not though - 'cause my old brakes definitely had much less advantage than these.

Sounds like your issues of mechanical advantage have more to do with low quality parts than how they're adjusted. In the shop I run into this problem day in and day out on cheap bikes. Usually the problem has to to with a brake arm or lever flexing too much. Hence the bottoming out, which is never a desireable situation. if you're set on using the parts on hand I would say just keep the wheels as true as possible and the pads as close to the rim as you can get them. At least you'll be able to stop!!!
If it were me I'd just upgrade the canti's. Cane Creek makes a good, affordable set.
We would sell them at $40. As far as the levers. I think Sheldon makes a good point about the cable routing issues here, but I would consider the quality of the lever in question before considering routing options.
Good luck.

Yep...I also believe it's the quality of parts issue more than anything else. Conventional road levers should provide just the right level of mechanical advantage when used with standard cantis without having to alter straddle cable length.

I'm quite sure there's not a problem with the brake arm or lever flexing. By 'cheap' I didn't mean 'crappy' - by 'cheap' I meant the brakes weren't expensive; these are the Shimano basic cantilevers that can be had at Certain Fine Retailers for $15 a set. The lever didn't flex on the brakes that were on the bike before, either.

Finally, even if things WERE flexing then if there was no advantage problem the brakes would return to a neutral position with ease.

Fact is, I've converted the bike from 27" to 700C, and between having narrower profile cantilevers than before and having to mount the pads correspondingly lower to account for the shorter wheel, I've got more mechanical advantage in the old levers with the provided link wire than is appropriate.

So my question stands as before.

I've got an mtb that I converted for road use and I have these cable pull doublers with my cheapo v-brakes. to fix the problem. I have aero levers, so I don't think that's the solution unless the ones that you find are made to pull the correct amount of cable (i.e., something made for cyclocross bikes maybe?).

I don't remember the name of the things that I have but one replaces the noodle and the other looks like an eccentric pulley. Not sure how they would work on center pull brakes, but you could probably figure something out.

If nobody else can help you out with the name of these things, I can snap a pic of the things I've got. I think I might even have one leftover.

i ran into the same problem with my trek 520 using low-profile LX cantis with aero levers and Sun CR18 rims. the fork was meant to take narrower, larger diameter rims, so coupled with the low-profile cantilevers, which are generally not recommended with aero levers to begin with, were very powerful but spongey. i ended up using a long straddle cable to get a better feel and more brake clearance. in theory a wide straddle hanger would get the same results.

Ah! found what one of em was.
http://www.performancebike.com/shop/profile.cfm?SKU=2647&subcategory_ID=5221

Here's one for inline
http://www.precisiontandems.com/cat_pics/brtravelagentinline.jpg

What's the shape of the triangle formed by your straddle cable?

A wide based triangle gives you more brakeing power but less brake lever feel. A long narrow triangle will do the opposite. Generally, Shimano link wires have a little line etched on the disc. Aligning the cable with that line is supposed to provide the best overall brake performance.

Perhaps it's simply a spacing issue....between the pads and cantis, since you had to 'set' the cantis further in for the narrower rims...? This basically changes the link wire geometry, thus affecting brake lever action.

HOw about a picture of the brakes?

The situation: I'm rebuilding a 1984 Schwinn Voyager from 27" to 700c; basically off with everything but frame/fork/handlebars/stem/seatpost. I'm keeping the brakes cantilever, and the idea was to keep the old non-aero (diacompe) brake levers. Props to Sheldon Brown, whose site has been a neverending resource and whose workplace sold me about half the ingredients for the project.

I got the cheap Shimano cantis - they went on fine with the new rims, although I had to dremel some extra rubber off of the backs of the front pads in order to let them clear the brake arm and meet the rim right. Cabled everything up, adjusted the pads, fine. The problem is that the brakes have too much advantage and feel very soft. The springload of the brakes isn't enough to snap the brake levers back to a neutral position (the hoods provide some friction here too, but it's an advantage problem, I think), and it's easy to bottom out the brake levers on the handlebars.

If I was using the yoke & straddle cable system that were on the old brakes, I could just adjust the length of the straddle cable to fix this issue. But this is a Shimano setup with the link wire. Is the cantilever angle less than 90 degrees? Not yeah, but HELL YEAH.

I've lubricated the cables and housings and it doesn't seem as though there's an unreasonable amount of cable friction - this wouldn't have much to do with the too much advantage problem anyway. I tried to avoid routing the cables in an unneccessarily bogus fashion.

So what are my options here?

* a different link wire length?

* going back to the yoke & straddle hardware? Maybe with the uberwide yoke or some such?

Any of those would help if the mechanical advantage is actually excessive. A big part of your problem is the conversion from 630 (27 inch) to 622 (700C) wheels, which is going to put the rim closer to the cantilever pivot. This inherently increases the mechanical advantage. This would be true of any make/model cantilever installed on this frame with these rims.



* Just spending the $40 on some aero levers? I'm gonna hafta re-wrap the handlebars anyway since I jacked it up the first time and from the looks of things going aero won't make the cable routing any worse. But I reckon the aero levers will lead to the same advantage issues.

Maybe not though - 'cause my old brakes definitely had much less advantage than these.

Modern brake levers have return springs built into them, and calipers/cantilevers designed for modern brake levers have weaker springs than old style ones did. The lighter springs are also related to the reduced friction of modern cables and housing.

I would advise updating the levers. You might actually get good results with Dia-Compe 287V levers. These have reduced mechanical advantage, officially intended for use with direct pull ("V-type") cantis. Normally these shouldn't be used with traditional cantis, but because of the increased MA created by your wheel swap, they might just be the ticket. I can't guarantee this would work, but it's what I would try if I were working on this bike.

Sheldon "http://sheldonbrown.com/cantilever-geometry" Brown


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