On my Giant TCR Advanced SL I have mechanical ultegra R8000 groupset and every 7/8 thousands kilometers the cable constantly breaks(usually it should happens every 20 thousands kilometers). It happened five times in total, at the third time we changed the lever(the right one) but the cable is still failing. We also changed the cable housing length in order to prevent some bad bend in the cable, but is still failing.

Does anyone can help me with some advices? The cable breaks in the lever. I wonder if could be the rear mech or something else different from the lever, in fact the lever was defective and it was changed with a working one.

  • That does seem a little too often - the usual rec is new cables every 2 years or 20kkm or when shifting suddenly gets flakey. Are you using decent quality inner cables? – Criggie Jun 8 at 12:50
  • yep, we using shimano inner cable and from the second time we used stronger cable, but it still happening. My mechanical asked at shimano guys but they was was not able to provide decent advices. The first lever was defective hence they agree to change, but now they are little confused... – Giovanni Jun 8 at 13:01
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    I don't know how normal that mileage is, but I've seen plenty of cables break in Shimano levers. They even designed the lever cover plate that you can remove to get the broken cable out of there! – Swifty Jun 8 at 13:11
  • @Swifty the normale mileage is about 20k kilometers or 12,5k miles, but mine breaks around 8k kilometers or 5k miles – Giovanni Jun 8 at 13:16
  • Do you frequently transport your bike via automobile bike rack? I have seen cables kink from the rubber strap. This is especially prevalent with those that leave the cable in a taught position (three largest gears on the cassette or the larger crank rings) – mikes Jun 8 at 21:21

This problem happens enough across the board with all recent STIs, especially on heavily ridden bikes, that there may be an element to it where the bends the cable is being subjected to is the real problem and there's some inevitability to it. But it's happening to you especially often. Here are some possible reasons:

  • You shift a lot.
  • The fancy nosed plastic Shimano ferrule isn't being used at the shifter.
  • Friction elsewhere in the line, like from overly tight routing or any of the other causes for it that contemporary road bikes sometimes create, is causing you to need to be more forceful with the shifter, causing the first bit of cable to see higher loads on it.
  • The cables have been getting installed in a manner that kinks them near the head. Then when combined with the tight bends that are inherent to this shifter, some strands are experiencing heightened fatigue and breaking prematurely.

Kinking the cable on this shifter during replacement is a fairly easy mistake to make, especially if you're not unwrapping the bars. The easy way to install the cable is to feed the whole thing through first until the end is resting in its seat, and then feed the whole thing back the other way, then into the tip of the ferrule. The trouble is if the ferrule is rigidly taped down and in place, it's easy to create a kink in the cable just ahead of it, especially with the nosed ferrules that one really should be using. The way to avoid this is feed the first part of the cable in and back the other way, but not pull it all the way through, and use a pick or small flathead screwdriver to guide it into the ferrule. Then gently push it through the housing bit by bit, and only seat the cable head in the shifter when it's all the way through and you can pull it into place without any of it getting bunched up and then kinking. Failure to do this is a way to cause the cable to break at the shifter.

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  • What do you mean with recent? Because I had the previous generation of Dura-Ace and it never happened. Everytime I(more precisely the mechanic, and he is not changed) change the cable i change the tape and also che cable housing. I ride roughly 20-25 thousands km per year. I had others bicycle before this and the cable always lasted more than 20 thousand km... I think that maybe could be some dysfunction of the groupset. Could be the rear mech? – Giovanni Jun 8 at 17:33
  • @Giovanni I heard it has to do with a really small cable spool after a sharp bend, which makes the cable flex significantly and rapidly fatigue. – MaplePanda Jun 8 at 22:01
  • @MaplePanda actually tonight when i was sleeping I realized that maybe could be a wrong inner routing and the cable can overlap the other cable... anyway i ask the mechanic to seek eventually sharp bend/inner overlapping or some defects of my frame... – Giovanni Jun 9 at 5:20

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