Centering cantilever brakes

[The Family Cyclist]

(disclaimer I've only ever had one bike with cantis and that was a BSO so excuse lack of knowledge)

My friend Simon now off this parish has been persuaded to get a tourer. It's a rather nice bike but he said the rear brakes are touching the tyre on one side. NP thinks me assuming it'll have V brakes but no it has Cantis. Sure enough one was pointing up too much so touching tyre, easily fixed but they were very lop sided. RH one pushes the rim away from it before the LH one touches. Previous owner had wound the little adjuster Allen grub screws in to try and centre it but it hasn't worked

On the part that hooks onto the straddle cable were two small Allen bolts along the bottom and a larger one at the top which also clamps the main brake cable. Do these need to be released so the straddle cable can be centred better and then worry about getting sufficient pull?

[Brucey]

most likely the fault lies in the springs (eg in the wrong hole in the boss) or in the pivots (eg binding).

You should disassemble and check these things before you do anything else.

Specific cantis have specific features too so it would help if you say what brakes they are and/or provide a photo.

cheers

[The Family Cyclist]

I think they are tektro cr 710 and found a pdf that confirms they need to be centred before the cable carrier is tightened on the straddle cable although I will suggest taking off, cleaning and checking they're in the same spring holes

[Paul]

Check the wheel is in straight too. In fact, do that first.

[citoyen]

most likely the fault lies in the springs (eg in the wrong hole in the boss) or in the pivots (eg binding).

IME even if the springs are in the matching holes, you might need to adjust the tension, for which there should be a screw in one or both of the arms IIRC. (It's a while since I've tinkered with cantis so I might be misremembering.)

[The Family Cyclist]

Ah glad you said that Paul as I said exactly the same thing when he messaged me then completely forgot when I actually got to the bike. I did ask if he had taken wheels out but brought it home on train

Citoyen it has got the adjustment but corresponding ones were wound right in on closest side and wound right out on the other but hadn't resolved

[citoyen]

Citoyen it has got the adjustment but corresponding ones were wound right in on closest side and wound right out on the other but hadn't resolved

In which case, the springs being in the wrong holes sounds quite possible.

In the past, I've had most joy in getting cantis to work properly by completely stripping them down and cleaning thoroughly.

[Brucey]

CR710.

IIRC these brakes rotate directly on the bosses (rather than having an integral pivot bushing like most shimano or Avid models), so need to be removed, cleaned and greased from time to time. Both arms have spring adjusters on them but this does not obviate the need to the springs to be put into the same (usually middle) holes on the boss. That the spring adjusters were set  differently each side and the brake was off centre still is quite telling.

If you encounter brakes of this sort that won't centre, the logic is that they were presumably centred at one time but since then, 'something has happened'. It is therefore a question of finding out what and if it ain't obvious you should start at the most common problem areas and/or the first steps of the centring process and then move on from there.

cheers

[The Family Cyclist]

Paul wins

Messaged my mate and the wheel wasn't in properly. I should have remembered as had an inbred that with usual quality control was prone to such things

[Paul]

 

[citoyen]

the wheel wasn't in properly

Classic.