brake caliper pinch bolt - how tight?
12-11-10, 04:09 PM
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brake caliper pinch bolt - how tight?
tightening the cable pinch bolt on a brake caliper, (or vbrake, or cantilever), how tight should it be? i've always tightened it down as much as i could. today when i went to reinstall the rear cable to the pinch bolt i noticed i'd crushed the cable to the point where one of the treads had broken.
how tight should it be? i understand there are manufacturer's specs but i don't have a torque wrench.
thanks!
ps - should i replace that cable? there's dozens of threads in the braid so i assume it's not just going to unravel and fail on me.
how tight should it be? i understand there are manufacturer's specs but i don't have a torque wrench.
thanks!
ps - should i replace that cable? there's dozens of threads in the braid so i assume it's not just going to unravel and fail on me.
Last edited by tgrssn; 12-11-10 at 04:13 PM. Reason: ps
12-11-10, 04:17 PM
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well, it's a bit hard to explain, but you should be able to get it tight enough by tightening the bolt with one hand, and the allen key in the low leverage position. i.e. stick the long end into the bolt, and tighten with the shorter arm.
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12-11-10, 04:38 PM
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The real danger of over-tightening the pinch bolt isn't crushing the cable, but breaking the bolt. It's only a 5mm screw, usually of brass or non-heat treated steel, so you have to use a bit of touch.
Some brakes have non rotating washers with grooves that can grip the wire without crushing it, but otherwise some crushing is required to get a good hold. If you're not sure if it's tight enough, squeeze the lever as hard as you would in a panic stop, namely with just about all your strength, or at least enough to lock the wheel on a rainy day. If you can do that without the cable slipping it's fine and will hold in the real world.
Some brakes have non rotating washers with grooves that can grip the wire without crushing it, but otherwise some crushing is required to get a good hold. If you're not sure if it's tight enough, squeeze the lever as hard as you would in a panic stop, namely with just about all your strength, or at least enough to lock the wheel on a rainy day. If you can do that without the cable slipping it's fine and will hold in the real world.
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12-11-10, 04:46 PM
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I generally tighten them as much as possible without shearing the nut. I always grease the threads to get them tighter. Caliper brakes seem to require more torque than cantis or V-brakes to prevent cable slippage (depending on the setup.) Those little things that the cable slides through on caliper brakes don't seem to hold as securely as the slotted systems on V-brakes.
I don't like crushing cables, but sometimes it's necessary. If you want to use a fresh section of cable without replacing it, you could trim your housing if it's excessively long.
I don't like crushing cables, but sometimes it's necessary. If you want to use a fresh section of cable without replacing it, you could trim your housing if it's excessively long.
12-11-10, 06:32 PM
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I dunno about that... I'd say it's more like 1/2 to 2/3 of the force you could use on the longer arm. Anyway, it's easy to get a feel for it with a bit of experimentation - as FBinNY said, just tighten it until you can't pull it through.
One or two broken strands is no big deal, especially on the rear.
One or two broken strands is no big deal, especially on the rear.
12-11-10, 07:18 PM
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How old is the cable? If it has broken strands, it may be a good time to replace BOTH cables. Cheap insurance, in my book.
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