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Derailleur and brake wire clamping force

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Derailleur and brake wire clamping force

Old 12-06-22, 11:10 AM
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Derailleur and brake wire clamping force

Clamp excessively and you might be cutting wire strands.
Not enough clamping torque and the wire might slip under sudden high braking force.
There are torque specs for the clamp bolts.
However, with the advent of polymer coated wires it has been suggested that the clamping torque might not be enough especially under heavy braking conditions due to the applied polimer.
So, to be on the safe side, especially for the brake wires, scrape the clamping area to remove the polymer before applying the torque.
Any views on this.
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Old 12-06-22, 11:43 AM
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If it slips on me... and sometimes they have, I tighten them more. Sometimes I had to tighten them more a couple times. No torque wrench required. No scraping required.
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Old 12-06-22, 11:46 AM
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Agree 100%. I've never had polymer coated brake cables but I have used polymer coated shift cables. Even tightened excessively, these slipped enough to affect shifting accuracy. Since then I've avoided buying coated cables and scraped the coating off the clamping area for the ones I still had.

Given good quality lined housing, cable coating is unnecessary and can be a liability.
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Old 12-06-22, 11:59 AM
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If you need to use more clamping torque on polymer cables, I would flip the washer under the clamping bolt.

Washers are stamped out of sheet. The tool always produces a slightly rounded edge from impact and a sharper edge as it exits the material. The duller the tool the worse the bottom edge.

While I have never flipped a washer to put the rounded edge against the cable, if I were having issues with the cable being cut I’d try that. It would seem that a rounded/chamfered edge would be less likely to shear the cable under force.

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Old 12-06-22, 01:00 PM
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IME the torque I put using a torque wrench is high than I did by feel. on new stuff that often comes with slippery cables I use manufacturers spec for torque and have not had any slippage issues
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Old 12-06-22, 01:09 PM
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The maximum torque depends on the screw (diameter, pitch, and material). Up to that limit find the torque that does the job. If you find or suspect that slippage may be an issue go higher subject to the maximum. Logically coated wires might want more clamping force, and if that's an issue I wouldn't use them for brake cables, especially the front.
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