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Brake cable tightning???????? Deraleur cable tightning?????????

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Brake cable tightning???????? Deraleur cable tightning?????????

Old 10-06-15, 12:37 PM
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elmore leonard
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Brake cable tightning???????? Deraleur cable tightning?????????

I see a lot of cables freyed at the fastening bolt. My question is this. How tight do these cables need to be secured at the fastener? Is there a torque spec for this? Is it common to over tighten them and damage the cable?
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Old 10-06-15, 12:53 PM
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Properly tightening the cable will flatten and bend it a little bit at the fixing bolt.
The end should be cut a couple of inches below the bolt and have a protector crimped on.
Yes, most mfgs specify a torque for the fixing bolt. For example 6-8Nm for most Shimano brakes.
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Old 10-06-15, 12:56 PM
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I expect that most of the time you see this it is on cables that have been disconnected and reconnected multiple times.
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Old 10-06-15, 01:17 PM
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The torque spec is a function of the fastener used, and typically low. There are a number of places to look up torque specs for fasteners based on thread and material. Given that these are not high strength cap screws, I'd say that the max torque would be about 7nm or so.

In any case, you cannot clamp these cables tight enough not to slip, without crushing them, especially brake cables which carry high tension. If there's 2" or so of cable beyond the clamp, that crush will not cause fraying. But the cut end will unravel over time, so a crimp, or glue, or solder, or heat shrunk tubing over the end will keep the job looking better.
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Old 10-06-15, 01:22 PM
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Originally Posted by FBinNY View Post
If there's 2" or so of cable beyond the clamp, that crush will not cause fraying.
That is an interesting observation. I've always left plenty of extra cable since it allowed for clipping off the fraying portion and recapping if I had to remove them for maintenance reasons. I guess this is yet another reason.
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Old 10-06-15, 01:44 PM
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Fraying at the anchor bolt is usually because the anchor is not designed to hold the cable without fraying. Draw bolts drilled for a cable to pass through are particularly prone to fraying because of the shear forces placed on the cable:



Campagnolo used a better design that spreads the load over a longer section of cable and eliminates the shearing force that a drilled draw bolt produces:



But the answer your question, the torque only needs to be enough to hold the cable without slipping. Over-torquing a drilled draw bolt will likely shear some cable strands and start fraying. Over-torquing a Campagnolo-type anchor will just flatten a short section of cable.
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Old 10-06-15, 02:29 PM
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If you see fraying (which I do on my bike), should they be replaced? How soon?
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Old 10-06-15, 02:45 PM
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Originally Posted by Fly2High View Post
If you see fraying (which I do on my bike), should they be replaced? How soon?
Fraying beyond the pinch bolt is meaningless (except for cosmetics and sticking your fingers) and can be ignored. Over time you may start to see fraying on the business end at the pinch bolt. If/when that happens the cable is losing strength and you should schedule a replacement at the first opportunity. Not an emergency yet, but the beginning of the end.
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