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Is is a shifter cable ruptured/torn near the inner end a usual defect with the ST-R7020 shifter or alike?

Torn shifter cable from ST-R7020

Some words on the symptoms when this defect happened (might help others with diagnoses):

Shortly before this happened shifting was limited to the smaller cogs. Eventually shifting to the larger cogs suddenly failed. No or at most one audible "click" can be heard or felt when pushing the longer, outer lever to shift to the larger cogs. The lever movement was limited in its distance. Shifting down using the small lever worked (once after the failure or when shifting up "engaged").

This happened after ~9.000 km on a 2y old bike/shifter.

In over 25 years I had three different shifters like the SL-M shifters, XT, Deore, SIS. Never had the cable fail there. Brake cables yes, but not shifter cables.

The only idea I have at the moment: it could have been caused by the problem with the RD-7000 cable mount due to increased forced due to the friction.

Is this a usual defect?

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    For how long before the cable snapped did you notice problems with rear shifting? Now you know what that means.... Sep 2, 2021 at 21:39
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    For comparison, I get 50-100km of warning , starting with thinking "that's funny, I adjusted that cable a week ago". As many of my rides are considerably longer than this, I carry a spare and know how to change it at the roadside - it's not hard
    – Chris H
    Sep 3, 2021 at 8:37
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    try { shiftgear(); } catch shiftingError { checkCable(); } finally { endRide(); }
    – Andy P
    Sep 3, 2021 at 10:45
  • Interesting thing while installing the new cable: after feeding it through and pulling it out again, it had a kink at the position where it bends from the Brifter to the drop bar. Man. Sep 5, 2021 at 17:44

3 Answers 3

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The cable turns a double right angle in quite a small space. It's a very common failure on all the 11speed shifters from 9000/6800 onwards. The "solution" is to change the right hand cable at a regular service interval, perhaps 2/3rds of the mileage you did with the current cable. One benefit of the new design is that it is considerably quicker and easier to remove the head of the broken cable than the older designs.

Note that you don't need to replace the outer casing unless it's damaged, it lasts much longer than the tortured inner cable.

In response to below comments, older generation shifters can also fail in the same way but the frequency of failure of the newer design is significantly higher than the 10-speed hidden cable shifters (5700,6700 etc). Tiagra 4700 and Sora R3000 use similar routing and may fail with a similar number of shifts but I don't have many of these systems in the wild so can't comment definitively.

Source: Busy workshop predominantly focussing on road.

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    This has been a "feature" of every single Shimano under-the-bar-tape shifter since DuraAce 7900. Happens on Ultegra 6700 too. Happens on 105 5700 shifters, too. Frayed cables and crappy shifting - relative to the same level free-flying cable shifters, anyway - is the price paid for under-the-bar-tape shifter cables. DuraAce 7800 is still the finest-shifting groupset I've ever used. Sep 2, 2021 at 21:42
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    Even Sora 9-speed goes in the same way, every time (@AndrewHenle)
    – Chris H
    Sep 3, 2021 at 8:32
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When I was putting serious mileage on a road bike, changing the inner shifter cables was just proactive maintenance, and I'd do it yearly which was 8-10 thousand km.

If your inner cable is under high tension during shifts (ie is hard to press and takes force) then inspect further down the line, looking for causes. Could be your rear loop of outer is too short, or some other cause of friction is in the line.

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    Indeed, shifting became harder in the last couple of months (obviously because of the frayed strands). Yes, the other friction could be the derailleur issue I've linked in my other question. Now I know. :) Sep 3, 2021 at 5:11
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These happen with nearly every shifter, no matter what type you're using. The failure mode is fatigue on bends.

The problem is that bend diameter ratio of cables should be 72 for long life, with 42 being an absolute minimum.

This means bending diameter of 1.2mm cables should be 86.4 mm with 50.4 mm being an absolute minimum. Thus, the bending radius should be 43.2 mm with 25.2 mm being an absolute minimum.

I think you'll find that nearly every shifter, including many types of trigger shifters (STI or Rapidfire MTB) and the most durable ones like downtube, thumb and bar-end shifters violate this rule pretty severely.

Thus, the cable will fail unless replaced. How long it takes to fail depends on how many times you use the shifter per kilometer and how many kilometers you ride per year. This illustrates that it may not be such a good idea to continually shift on a "corncob" road cassette having 11-12-13-14-15-16-17-... tooth sprockets. It may be a better idea to use a cassette having few sprockets, large jumps between gears and only shift when you truly need to shift, i.e. when encountering such a steep uphill that you can't tolerate it with your usual flatland gear.

Fortunately, the cable will last far longer than for example a Di2 battery charge, so we need not move to electronic shifting. All it requires is replacing the cable every year or two. Usually the shifter designs make it reasonably easy to change the cable. In contrast with drop bar "aero" brake levers with under-the-bar-tape cable routing, in which case changing the brake cable might require rewrapping the bar tape because you might not be able to hit the housing taped under the bar tape no matter how many times you try (at least this is a problem with BL-R400), shift cable replacement is easy.

By the way, cable failures can happen for brakes too (they having 1.6mm diameter should have ideally 57.6 mm bending radius and 33.6 mm bending radius at a minimum -- in many cases, this bending radius limit is observed and thus the failure is not due to fatigue but rather due to wear). In this case, it's a safety hazard. Installing a new brake cable every now and then is recommended.

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