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I have a roadbike with an older Shimano 105 set of brifters. The left hand / front shifter has always had problems getting the chain to the big ring, to the point I often have to dismount to reset the chain.

Recently someone pointed out that my shifter outer was "weird-looking" and I had no idea, because this was all hidden by my stem while riding normally.

enter image description here
sorry for fuzziness - was a balancing act

The outer lies normally when untensioned but twists like this when I change to the big ring only. Shifting to the middle ring from the grannie works fine.

What has caused this? It used to work acceptably but has never shifted well.

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    I suspect the cable shell is wonky. It may have a broken strand or some such. – Daniel R Hicks Dec 14 '20 at 23:24
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    Replace the cable and the housing if this happens under tension. – Carel Dec 15 '20 at 9:12
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    Wouldn’t you usually go around the other side of the head tube and then cross under the down tube (if that’s necessary)? I think this is just not visible in a normal installation, I’ve never seen this much free-running shift cable. – Michael Dec 15 '20 at 10:17
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    @Michael: In the beginning all STI shifters had hidden brake cables, that technique was in use before STI but the gear cables ran out of the hoods. After several years only Dura-Ace went into aero-mode while Ultegra and 105 took much longer. Personally I think that the open air cables (like those in my Ultegra tri-color) are much easier to replace. – Carel Dec 15 '20 at 14:16
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    @Carel: Yes I know and I’m still under the impression that they worked better (less friction) than even the most recent shifters with hidden cables today. We lovingly called them „Wäscheleinen“ (“clothes lines”) in German. – Michael Dec 15 '20 at 14:47
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The corkscrew shape of the housing strongly suggests that the cable is under great tension, and putting excessive compression on the cable housing. Since the cable doesn't completely fill the housing, it will be ever so slightly shorter around a curve than the housing that contains it. You've put so much tension on the cable that the housing is bending under the pressure.

The most likely cause is that your derailleur is seizing up at the end of its range; normal pressure will move it over the lower part of the range, but it takes extreme pressure to move it the last bit. I would inspect the pivots for rust or dirt, clean them and apply penetrating oil and see if you can loosen it up that way.

I see some suggestions of a broken cable strand; I wouldn't expect that to cause a problem only at the end of the action. But if a strand is broken just where the cable exits the cable housing at the bottom of the down tube, it could be hanging up just inside the termination of the housing. But in that case the other end of the broken strand would be visible in the exposed length of cable, which I assume you've checked.

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  • You are correct! The front mech had moved subtly on its mount, and was right at the limit when pushing to the big ring. Notice in the picture above, the downtube mount just visible is also slightly rotated - there has been enough pressure and leverage to turn the stop a little, also messing with the tension. And its using "performance" inner cables which are indeed slightly thinner and slipperier, allowing the outer room to fold up like a loose sock. – Criggie Dec 15 '20 at 18:32
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Just based on your description, my best guess is that some of the strands of the housing have pushed past the housing end and are pushing into the lever. Unhook the cable end at the derailleur so you have some slack and can pull the housing back from the lever and inspect that end.

While you have it loose, also push the cable head out so that you can check for any fraying near the end of the cable. That's the common failure point for cables in these STI shifters.

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    That is an excellent idea and loose cable strands could certainly cause weird shifting. The older STI levers were renowned for eating inner cables in as little as a year when used hard, with the first sign being poor shifting then a snap and no shifting. Having the outer's reinforcing in the wrong place would also do weird things requiring more tension. So +1 for you! – Criggie Dec 15 '20 at 18:36

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