aaronmichael

Alright bicycling friends, getting frustrated with this one. Bought some Tektro CR720's to make an old M500 look a bit more modern (also the original cantilever arms were rusty) but can't seem to get the Tektro brakes to work correctly with the original weird spring loaded cable stop mechanism. After installation, the spring mechanism was acting like a cable stop, and therefore the right brake arm would move but the left one had absolutely no actuation when the lever was pulled. Is there something I could install around the seat post or seat post clamp to change this to a traditional canti system with a yoke and straddle cable? Do the geometry of these brakes simply not work with the original mechanism? Should I set the Tektro's at the lowest hole in the canti studs so the pressure of the springs isn't too much for the spring loaded mechanism? Any help would be greatly appreciated, thank you!

https://www.dropbox.com/s/7tzxud8lgm...2016.43.51.jpg

FBinNY 

You have a few choices.

1- you can correctly route the cable through the cam, so that when you apply the brake, the wire pulls one arm, while the housing pushes the cam, rotating it and pulling the wire to the other arm.

2- you can replace the cam with a cable hanger made to fit fork crowns. Make sure it's mounted properly and tight, preferably with a star washer so it cannot rotate. Now that there's a cable hanger, you can proceed with a standard canti installation.

3- you can dispense with the cam and it's mount, and ise a hanger that attaches to the seat post pinch bolt (may not work on all bikes), and proceed with standard canti cable configuration.

Given that the cam is already there, I'd start with that.

BTW, please don't take offense here, but seeing what you've done so far -- the housing hanging without a fulcrum (stop) of some kind, and the wire attached only to one arm -- I'm concerned that you lack a basic understanding of how brakes work, and suggest you visit a bike co-op, or shop and get some help. I don't say this to hurt your feelings, but for your own safety, and once someone helps you with the basics, you'll thank me for sending you there.

Andrew R Stewart 

The cam acting casing stop on Cannondales (and available BITD as an aftermarket "upgrade") was an attempt to increase the force of the pads against the rim. As many already know this required a reduction of pad/rim clearances (and remember this is before the advent of linear pull compatible levers which pull more cable). But as many found out the inclusion of a third pivot created more problems of adjusting the pads from rubbing the rims.

During the 1990s we say a lot of Cannondales coming through our shop with brake rub issues that used this arrangement. Initially we tried to make the stock set up work. And it would work well enough UNTIL it saw real trail conditions and some wear/use. The bikes would be back soon enough and we'd do a second adjustment round at N/C (as a shop that prided ourselves doing good service we had a 30 day service warranty). After a number of these go rounds we started to by pass the pivoting cable stop with traditional hangers (attached in various manors depending on the location and bike's options). This would ALWAYS fix the rubbing issues. Of course the brakes would not be quite as powerful, although the feel at the lever firmed up (a feel that I like).

So my suggestion is to ditch the cable stop pivot and use a frame/fork mounted hanger. Andy.

aaronmichael

Thanks for the replies gentlemen. FBinNY: I was in a rush to take a photo so thats why it was disconnected. I've actually been a mechanic for a couple years now. I'll admit I don't have a lot of experience with cantilever brakes, I do understand how they work and how the cam works though. The frame/fork mounted hanger does seem like the best option right now. I wasn't even aware that those existed. Now would that TRP hanger work as a replacement for both the front fork cam and the rear cam, or would I need a different variation for the rear?


Thank you both again for the input and information!