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My rear derailleur shifter cable just broke for the third time in two years 5000 miles/ 8000km. I was lucky this time. It broke a mile from the end of a long ride.

What am I doing wrong? Are there cables that don't break as easily? Or do I just have to replace those cables every 1000 miles?

Edit It breaks inside the shifter, right where it's the biggest possible pain in the xxx neck to get the broken mushroom head out.

The design is pretty bad. The very end of the cable wraps around a small-radius capstan, and gets bent when downshifting and straightened when upshifting. My high school physics teacher showed his class how to do that repeatedly to induce metal fatigue and break an otherwise strong stainless steel cable.

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  • 1
    I'm assuming you're not using cheap junk cables here but your experience is not normal. I've never ever broken a shifter cable. Perhaps there is a problem with the cable routing or your rear mech. Perhaps a photo or two of the setup would help.
    – jwh20
    Oct 11, 2021 at 1:07
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    Can you measure how far from the mushroom head the cable broke? IE, did it fracture inside the shifter, or somewhere else on the run?
    – Criggie ♦
    Oct 11, 2021 at 1:43
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    Do you chage the outers at the same time or are they original ?
    – Criggie ♦
    Oct 11, 2021 at 1:44
  • 4
    Where is the cable breaking? If it's inside the shifter body its a known issue with shimano 10 speed sti levers. Typically in my family bikes get serviced every year which includes new cables, but if they get forgotten and it stretches to more like 18 months a broken cable acts as a reminder.
    – Andy P
    Oct 11, 2021 at 8:10
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    It’s pretty common for the cable to break inside the shifter. Usually you get early warning because shifting to the smallest sprockets no longer works. Low friction and good cables help.
    – Michael
    Oct 11, 2021 at 9:08

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