Side pull problem...

[alan dun]

Brake prob..
Thorn audax on 700 wheels, mavic rims.
the Shimano side pull 47/57 drop (front brake) is rubbing the tyre wall (28mm tyre). At the lowest setting it rubs about 2mm of tyre wall.
Can anyone recommend an alternative side pull which would give about 61mm drop.
Have checked the wheel sitting in the fork, centering, etc it all seems ok.
Alternatively what am I doing wrong..!
thanks...

[Jdsk]

Was it always like this or has something changed?

Please could you add some photos.

Jonathan

[Carlton green]

I can’t directly solve the issue but recently had something similar when I changed (renewed) brake blocks. I eventually ended up using different new blocks and that then gave me the clearance that I needed, but my solution might not work for others. (IIRC I ended up with Fibrex Ash 470 blocks.)

Happy to try to help and, of course, hoping to hear how the OP resolves the problem.

[KM2]

Is it possible to use a round file and take 2 mm off at the bottom of the slot, assuming enough alloy there?
If it’s only just happened try recentering the wheel. Undo, press down on the handlebars to centre.

[alan dun]

Not keen to file down the brake hanger..
can certainly try different blocks, these are Aztec.
it's on my 2nd tyre now..hadn't spotted it before, so it's not new..
thanks guys

[Norman H]

Are these new brake blocks and if not how worn are the old brake pads?

With side pull callipers the contact patch between rim and pad progressively moves towards the tyre as the pads wear. This can result in the type of tyre damage that you describe.

[pwa]

I'd possibly take a brake caliper off the bike and have a good look at it from all angles, and under good lighting. In particular, I'd be looking to see if there is something about the way the brake block sits in the slot that prevents it going all the way down.For instance, is some of the rubbery material extending out along the metal that goes in the slot. If it were just that, a bit of sandpaper would fix it in no time.

[peetee]

When you say ‘side pull’ are you referring to the (now, almost universal) dual pivot brakes?
If so, there are two ways of centring the brake and if done wrongly one brake arm will sit higher than the other and move towards the rim with a slight upward trajectory.

[alan dun]

Many thanks for all the help.
I've added a side profile photo of the problem brake. It seems to be centred pretty well, but I'm a bit baffled...

[PT1029]

Try mounting the caliper a bit off centre, ie, mount so the side opposite to the cable is a bit low*. If you can lower this by 2 -3 mm, then see if you can recentre the brake using the normal centring screw.
If this seems to work, check if it looks like it will still work with a worn pad (ie, when the caliper arms swings in and up more as the pad wears).
*This is usually the side that is likely to rub a tyre.

Replacing with a deeper caliper will give better braking. Brakes set with the pads right at the bottom have a lower mechanical advantage.

[slowster]

If you replace the brakes with Tektro R559 calipers, the pads will then be close to the top of the slots and you will probably find that the braking is improved due to the increased mechanical advantage (see the comments of this poster here - viewtopic.php?p=957906#p957906).

https://www.spacycles.co.uk/m7b0s100p14 ... %28pair%29

However, I *think* you might be able to fix your problem by just replacing the moulded blocks with cartridge holders. I suspect that the moulded blocks have, as it were, 'too much' pad material above the nut which is in the block. In other words, a minimum amount of moulded material is needed all around the nut for 360 degrees in order to ensure the strength of the structure and the bond of the nut in the moulded material.

That is not the case with metal cartridge holders, and consequently the removable pads that fit in them can be narrower. For the most part I think the various cartridge holders that take Shimano pattern pads are much of a muchness, and there is little to choose between the more expensive Shimano or Kool Stop brand versions versus the cheaper Clarks and Ashima etc. versions.

I have the Ashima version in my brakes, so on the basis that that is what I am already familiar with, I suggest you buy those, together with Kool Stop Salmon pads to replace the pads supplied with the Ashima cartridges. If that does not cure the problem, I would then buy the Tektro R559 brakes. The money you would have spent on the Ashima cartridges and Kool Stop Salmon pads would not be wasted, beceause you would be able to fit them to the R559 brakes in place of the inferior moulded pads they are supplied with.

https://www.sjscycles.co.uk/brake-block ... d-shimano/

https://www.sjscycles.co.uk/brake-block ... e-inserts/

[rjb]

As the brake blocks wear the fixed pivot causes the block to approach the rim at an increasing angle which raises the block. You could try adding a thin washer between the arm and the block and check if that improves things. A simple solution which is easily reversible if it's ineffective.

[531colin]

Y'know, that "Slowster" has an annoying habit of being right!.......

002 by 531colin, on Flickr

Thats not a sidepull brake shoe (or holder, if thats what we are calling them these days) its a cantilever one, and i think its probably a "KoolStop" brand....i haven't had sidepull brakes for many years.....but just compare it with the OP's picture (click to enlarge) and the OP's brake pads seem to have more above the fixing bolt than below it.

Worth re-emphasising that on a dual-pivot brake, as the pads wear, one goes up and the other one down, relative to the rim.

[alan dun]

Ok, seems after a morning of trying things out to have worked out my brake problem.
My bike is fitted with a Cytronex power assist system.
The axle on the Cytronex front motor drivewheel is made from 12mm material, and machined on two sides with flats to 9mm, to fit the forks.

The front fork ends have 9mm openings and radiused as per normal to take the front axle.
The Cytronex axle (from 12mm) does not sit as far into the fork end as it should and that is enough to misalign the brake pads.
A slight modification to the axle would solve the problem, I will let Cytronex know.
enjoy the bank holiday..

[rjb]

Ok, seems after a morning of trying things out to have worked out my brake problem.
My bike is fitted with a Cytronex power assist system.
The axle on the Cytronex front motor drivewheel is made from 12mm material, and machined on two sides with flats to 9mm, to fit the forks.

The front fork ends have 9mm openings and radiused as per normal to take the front axle.
The Cytronex axle (from 12mm) does not sit as far into the fork end as it should and that is enough to misalign the brake pads.
A slight modification to the axle would solve the problem, I will let Cytronex know.
enjoy the bank holiday..

Time to break out the file.

Just to be clear, the file is to trim the axle slot so it sits securely in the drop out. I'm not condoning filing the brake arm slot.