Inefficient brake

[taximan]

For some time now I have had little effect when using my rear brake. The brake lever feels firm when I apply it but but the brake has little effect. It is impossible to lock the wheel, (not that I would want to) and using the rear brake alone would not stop me on anything but the gentlest of slopes. I tried new blocks without success, (I use the same blocks on my other bikes and they are fine). I tried a different make of blocks, again, without success. I then called in my mobile bike mechanic and the only fault he could find was that one of the grub screws was cross threaded which I already knew about so he drilled it out and tapped in a larger thread as a tempory measure. It looks a bit Heath Robinson but it works OK. Incidently I have just replaced the wheel but the problem was there while I was still using the old one. The bike was returned yesterday and my mechanic was as baffled as I was and all he could suggest was to replace the brake with a Tektra CR720. Can any of you guys offer a suggestion as to what is going on. I have been using the same bike man for a number of years now and have never had reason to doubt his ability.

 

[MichaelW2]

Clean the rims with a scratchy washing up pad.

 

[fossyant]

I've got the same brakes on my CX bike - they stop on a sixpence. I'd clean the rims and maybe change the pads to these ? I can very easily lock the rear wheel up.

https://www.decathlon.co.uk/p/tri-zones-900-v-brake-pads/_/R-p-337?mc=3153601

Also try shortening the straddle wire a little, should be a 45 degree angle in it and yours looks a little too long.

 

[taximan]

Clean the rims with a scratchy washing up pad.

Already tried that

 

[taximan]

I've got the same brakes on my CX bike - they stop on a sixpence. I'd clean the rims and maybe change the pads to these ? I can very easily lock the rear wheel up.

https://www.decathlon.co.uk/p/tri-zones-900-v-brake-pads/_/R-p-337?mc=3153601

Also try shortening the straddle wire a little, should be a 45 degree angle in it and yours looks a little too long.

The straddle wires are at about 45 degrees, I think the angle of the camera has affected the image.

 

[roubaixtuesday]

Sounds like a cable issue? A frayed cable would do this.

Have you replaced the inner and/or checked it's free of friction (detach at brake and operate lever, pull back by hand)?

Replacing outer may be necessary if it's friction.

 

[fossyant]

You can just make out mine. The straddle wire is much closer to the tyre.

 

[fossyant]

Its worth a try as its not going to cost you.

 

[taximan]

Sounds like a cable issue? A frayed cable would do this.

Have you replaced the inner and/or checked it's free of friction (detach at brake and operate lever, pull back by hand)?

Replacing outer may be necessary if it's friction.

The cable feels free enough but I was thinking of replacing it anyway. I am away on a four day tour in a couple of days so I will probably do that when I return.

 

[taximan]

Its worth a try as its not going to cost you.

I have just had a quick look and I think the brake cable is trimmed too close so I will try it when it is replaced.

 

[davidphilips]

All for shorting straddle cable as said above, zero cost and pull angles can make a vast difference, remember in my teens using an old bike with center pull brakes, when set up with a few adjustments they worked as well as any modern rim brake.
Theres always the option of changing to wee brakes but perhaps best just to spend a bit of time adjusting what is fitted.

Also pull the brake hard and look and see if theres any flex in you frame/ seat stays,if so then a brace costing about £4 may make a big difference?

 

[T4tomo]

My 2p is a shorter straddle wire too.

https://www.sheldonbrown.com/canti-trad.html

I had fun with a couple of bikes getting them set up right, but once set up they should be very powerful, its just finding the sweet spot so you have just enough clearance and enough mechanical advantage and travel.

I have just had a quick look and I think the brake cable is trimmed too close so I will try it when it is replaced.

I reckon you have enough free to work with, these adjustments are best done in small increments anyway.

re excess friction, that is more of gear shift issue with the cage not moving when tension is released. A brake cable suffering from excess friction might feel stiffer than it should but that just means you pull a tad harder and it may stick on. That isnt your symptoms.

 

[glasgowcyclist]

Already tried that

New bike it is then!

 

[presta]

Firstly, what was the last thing you changed before the problem appeared? Try undoing it.

Secondly,

The brake lever feels firm

Hints that the mechanical advantage of your brake is too low for the levers you're using, in which case the solution would be to flatten the straddle cable as Fossyant suggests.

 

[Ajax Bay]

The brake lever feels firm when I apply it

my mechanic was as baffled as I was and all he could suggest was to replace the brake with a Tektra CR720.

What brake lever are you using? Image of Tektros for info: https://fawkes-cycles.co.uk/tektro-cr720-cantilever-brake-in-black-p19588

I am away on a four day tour in a couple of days

You have at least 10mm of cable to allow the straddle to be dropped. Tell us you are not using this bike with an ineffective rear brake for your tour.