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How Much Cable Stretch is Normal?

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How Much Cable Stretch is Normal?

Old 11-17-15, 08:12 PM
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FlatFender
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How Much Cable Stretch is Normal?

New cables on a new road bike. Since picking up the bike, and riding about 300 miles, I've tightened the rear derailleur cable 4 full turns at the thumb adjuster on the derailleur. It's all been a quarter/half turn at a time to get it shifting better, but 4 full turns seems a little much. Is this normal?
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Old 11-17-15, 08:17 PM
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If the bike shifted well initially and 300 miles later took 4 full turns of the adjusting barrel, that's not normal. I expect the cable is slipping in the clamp bolt. Is the cable teflon coated and was the coating left on it under the clamp bolt? If so, there is your problem.

If the bike didn't shift properly right from the start, there was too much slack left in the cable at the initial installation.
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Old 11-17-15, 08:18 PM
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I don't think that's normal.

My suspicion is that, rather than your shift cable stretching, your cable housing is gradually shrinking. The tip off is that a quarter or half turn of the adjuster fixes it temporarily, but it degrades again.

Check out all of your cable housing ends. What you are looking for is one or a few tiny wires sticking out of the housing end cap. If you find that, remove the end cap, trim the end of the cable housing so that it's nice and square, and reinstall the end cap. My bet it that'll fix it.
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Old 11-17-15, 08:29 PM
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I've wondered about this also. But in reverse. Earlier this spring, I changed out brake levers and got new cheap cables and fully expecting them to stretch after some miles, I installed with all adjusters screwed all the way in. They have not stretched a bit so far.
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Old 11-17-15, 10:37 PM
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I really do think it's more a matter of the housing settling than the cable stretching. The cables just aren't under that much tension.

A lot depends on the quality of the install. The amount of ragged housing at the end of a sloppy cut can be worth a turn by itself - multiply by the number of housing ends. It could also be a problem like strands slipping through the ferrules at stops and levers.

Give it all a good look and if it doesn't settle in soon, re-do.
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Old 11-17-15, 11:19 PM
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Another check point is the shifter housing under grip tape. The housing can pull away from the stops on the levers when taping things down.
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Old 11-18-15, 12:11 AM
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The amount of stretch in cables (or compression of housing) is minimal, and might account for an adjustment of less that a quarter turn of the adjusting barrel. There is sometimes some settling of the fittings, or cable head in the lever, but this happens very quickly and only once.

Experienced mechanics spare themselves of needing to readjust due to settling by over-tensioning a cable before fine tuning on initial assembly. My favorite technique foe this is to pull the bare wire away from the frame at the downtube like a bow string.

If you repeatedly need readjustment over time, either the wire is slipping at the pinch bolt as suggested above, or a clamp on fitting may be slipping. One other possibility is housing pulled away from the lever under the tape and slowly creeping forward until it finally pockets fully into the lever body.
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Old 11-18-15, 06:29 AM
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Another possibility: a ferrule may be missing from one of the housing sections. This was the cause of abnormal "stretch" on a bike I worked on once. The metal housing liner was being pulled through a frame stop.
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Old 11-18-15, 08:19 AM
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Originally Posted by FBinNY View Post
Experienced mechanics spare themselves of needing to readjust due to settling by over-tensioning a cable before fine tuning on initial assembly.
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