Cantilever brakes not releasing

[ChrisEyles]

I'm just putting the finishing touches to a very nice Dawes Galaxy I've been given, and the rear brakes were the last on the list to sort out.

They clamp onto the rim fine, but won't fully release. If I give the cable a gentle pull the brakes will release fully, but the canti springs aren't up to the job themselves. I've tried everything I can think of over a very frustrating couple of hours! If anyone's got any ideas, I'd be very grateful.

I installed both cantilevers on the bosses with fresh grease, and have checked that the bolts holding them to the bosses aren't over tightened. The springs are also in good condition, cleaned and oiled, and well centred. Wiggling them back and forth by hand, they feel fine.

I've tried a few different yoke lengths and spacer combinations on the brake blocks, some of which caused the brake to release a little better than others, but still not adequately.

Both inner and outer cables are new, with no kinks or snagging points that I can see. The brake levers are the aero type (cables routed under the bar tape rather than out the top of the hoods) so it's difficult to see exactly what's going on in there even with the bar tape unwrapped - this is the next area I will investigate but I need a break first (pun definitely intended).

I don't know what it is about canti brakes but I always seem to run into some sort of problem whenever I work with them...

 

[biggs682]

do the canti's operate without the main cable connected ?

i presume you have the spring in the strongest hole ?

 

[Hugh Manatee]

Braking surfaces (blocks and rim) nice and flat? Spring tension adjusters, probably 2mm Allen key bolts on something that old. Do the two arms feel the same amount of springiness?

Maybe your sacrificial offering wasn't good enough? Try wailing and gnashing your teeth. It won't help the brakes but you'll feel better.

 

[ChrisEyles]

Spring tension adjusters are done up as tight as possible with the centering remaining good... but I'm fairly sure the springs are in the middle setting - good thinking @biggs682! I'll give that a go this evening.

 

[ChrisEyles]

@Hugh Manatee I've already tried the wailing and teeth gnashing It's standard operating procedure whenever I do anything with canti brakes.

 

[raleighnut]

I'd go with @biggs682 suggestion, use the strongest spring tension hole.

 

[Sheffield_Tiger]

What's the profile like on the rims?

I have a bike with a similar issue, the Campag Stheno rims are wearing so the walls have a curvature outwards - under pressure the pads wedge into place

 

[ChrisEyles]

I put the springs into the strongest position last night and that just about does the trick. There's still the last tiniest bit of cable that doesn't pull back through the outer when releasing the brakes, but it's small enough to live with. Just to make life difficult, Mrs Chris prefers a fairly high mechanical advantage on her brakes (shortish yoke cable) which means you have to start with the pads quite close to the rims or the brake lever bottoms out.

Thanks @biggs682! I put palm to forehead as soon as I read your post, don't know how I missed that one!

 

[JPBoothy]

It's nice to hear that I'm not the only Canti user these days, as everybody I know seems to think I'm some sort of Dinosaur for not having Discs. I even went to the trouble of tracking down an older model Cannondale CAADX on Gumtree because I didn't want the newer model with Discs (not because I'm tight ). They can be the most frustrating thing to set-up though can't they, but worth it when you get it right.

As for that little bit of cable that won't release. I also had this on a cable that ran underneath my bar tape and into the hoods, and after much of that teeth gnashing thing (and a few choice words) it turned out to be a small burr on the outer cable where I hadn't cut it cleanly before pushing it into the hood. It's a bit of a pain removing the tape but it might be worth a look.

 

[ChrisEyles]

I think the offending bit of cable is right up in the aero levers. There's a little plastic clip/clamp that the cable outer goes through which wedges up against the hoods, which is the location of the sharpest bend in the cable outer. I've squirted in a bit of GT85 but it still feels like there's a touch of resistance there pulling the cable through by hand.

I did round out the cable outers with a brad awl after cutting them so they should be nice and smooth and burr free. If I have any further problems I guess I'll take the cable out of the lever and start over, but @biggs682's observation seems to have done the job.

My commuter also has canti brakes. They work great when they're well set up but they do seem to be a lot more faff than calipers or vee brakes (I've never owned a disk brake bike and haven't had to do any maintenance on the hydraulic brakes on the 29er I borrowed for a while). For stopping power and ease of setting up/maintenance vee brakes are by far my favourites, and I think they look pretty smart too. I always think it's a shame they haven't made their way onto road bikes with a different cable pull action on the drop bar levers.