Brake binding on rim

[Globalti]

There's nothing wrong with the line of that cable, it's perfect. You can go well over that torque setting because you are only compressing solid material inside the brake bridge. Put some grease on the threads of the recessed bolt and all over the bolt itself to aid future removal then tighten it so that the first part of the brake, which is effectively its non-moving "chassis", is attached solidly to the frame with no swinging from side to side. The Shimano pdf says 8-10 nm for that bolt and explains how to use that little bolt on the end of the "chassis" to adjust centring: http://bike.shimano.com/media/techd...0A/SI-8JC0A-002-Eng_v1_m56577569830746290.pdf

It's worrying that the shop mechanic doesn't understand this fundamental point about brake setup - is it a proper bike shop or just a bike supermarket?

 

[boydj]

If the brake is slightly loose so that you can move it by hand with a bit of pressure, then it should centre itself when used. if this is not happening, then something is pushing it to one side - most likely the outer cable.

 

[Broadside]

There's nothing wrong with the line of that cable, it's perfect. You can go well over that torque setting because you are only compressing solid material inside the brake bridge. Put some grease on the threads of the recessed bolt and all over the bolt itself to aid future removal then tighten it so that the first part of the brake, which is effectively its non-moving "chassis", is attached solidly to the frame with no swinging from side to side. The Shimano pdf says 8-10 nm for that bolt and explains how to use that little bolt on the end of the "chassis" to adjust centring: http://bike.shimano.com/media/techd...0A/SI-8JC0A-002-Eng_v1_m56577569830746290.pdf

It's worrying that the shop mechanic doesn't understand this fundamental point about brake setup - is it a proper bike shop or just a bike supermarket?

Thanks, didn't know about that torque setting, but that is a calliper spec rather than what the frame can handle. Can you tell I'm a bit paranoid about writing off a frame !!

The shop is a 'proper' bike shop, they do custom builds and also run a race team that competed in the Pearl Izumi Tour Series this year, they build all 15 of their race bikes in house so I think they are pretty good. It's probably more that they didn't really listen to the severity of the initial report at the freebie service than the mechanic not knowing, they are a good bunch of enthusiasts in there. I'm going to take the bike back in there this week.

 

[accountantpete]

It sounds like the lock nut has not been set properly or the wrong size hex nut has been used..

What should happen is that the calipers are securely clamped to the frame between the hex nut and the silver starred locknut nearest the calipers so that they can't move easily to one side but still open and close very easily.

Take the wheel off , re-tighten up the hex nut to the normal amount and try to move the calipers to one side. If they move easily then you have the wrong size hex nut and this is bottoming out (there are at least 3 sizes to account for differing frame designs). If they tighten ok and don't move, check the locknut grub screw to make sure it is not moving.

 

[Globalti]

Yes, good point, I forgot that you often get a choice of hex nuts with a brake set to accommodate different frame bridges.