Jim’s Tech Talk
By Jim Langley
RoadBikeRider reader Bob AtLee asked this great question,
“Yesterday, after a month or so of sluggish shifting on my rear derailleur (Shimano 105 brake / shifter with an Ultegra derailleur) I finally peeled back the rubber hood on the brifter and lo and behold, there was the tangled mess of an almost-snapped inner cable, where the cable bends to go around a white plastic guide. My guess is it’s a couple years old, maybe 10,000 km on it. Being an old fart I shift a lot.
I’ve seen this before when my daughter’s cable actually severed, resulting in a complete loss of shifting on the rear and a ride finished on two speeds (the front derailleur only). Thank heavens we had come down to the flat country from a very mountainous ride (Icefields Parkway, Canadian Rockies). It took us a couple hours and some fine work with a dental pick to extract the moulded cable end from the shifter mechanism.
Is this endemic to the “new,” concealed cable style Shimano shifters? It sure – as – heck looks to me like they are asking for trouble, pulling that cable around a tight corner on nothing more than a Teflon guide.
Is there something a person can do to extend the life of the inner cable? Or is it a case of, well, one more thing for the annual winter service is to replace the index cable inners?”
I’ve seen enough STI shift cable failures inside the lever similar to what you’ve suffered, Bob, that I do think you’re correct and it’s a fairly common issue for people. But, I can’t remember ever having one of mine fail.
My friend Leo brought his bike to me to fix his broken cable and when I looked inside the lever I found the frayed mess but when I finally got the stuck cable head out, the lever still wouldn’t operate properly. I looked again inside the lever – but this time with a flashlight. And I was surprised to see another cable head wedged in there preventing the lever from working.
Apparently a previous mechanic had managed to replace the broken cable and had let the old cable head fall into the lever. Once I got that one out, and fed the new cable in, Leo’s shifting was good as new. I asked Leo about his broken cables and he said he was using inexpensive replacements, not Shimano’s. (But, I assume his Trek came new with Shimano cables so I can’t explain how the first one broke.)
Is It The Tight Bends In The Cable Path?
It’s tempting to blame the cable breakage problem on the design of the cable path in the lever. As far as I can tell, cables break on all the different models of Shimano STI shifters, not just the 105. And from the different models and different years STI has been on bikes the cable path has changed.
Could It Be A Bad Installation Or Cable?
I think there’s more to these cable breakages. For example, it’s fairly easy when installing STI levers, cables and housings to end up with gaps between the end of the housing and the pocket in the lever it’s supposed to sit in.
It’s also common for the cable housing to compress over the miles, which lets the wire housing liner protrude from the end. Both these issues could leave the inner cable unsupported and might lead to a cable breaking.
Another issue is the cable type and installation. Shimano recommends only using their cables and housings. On setups that require it, there should be ferrules on the ends of the housings. Also, the cable heads that rest inside the lever should be lightly greased before installation.
When installing the cables and housings, I like to make sure that there is tension on the cable so that the cable head remains seated in its pocket inside the lever and that the housing end stays seated in the lever body, too. If there are ferrules, I check carefully to make sure they’re fully seated on the end of the housing and that they seat fully in the lever.
Should You Replace Shift Cables Yearly?
I would hope you’d get more than a year out of your shift cables, Bob. It can’t hurt to look inside the lever to see if all’s well. But, I wouldn’t replace cables unless there were signs it was needed, such as fraying, housing issues, maybe corrosion.
I don’t know if this is true, but one of Shimano’s stated reasons for “upgrading” all its high-end road groups to their Di2 electric shifting is because it solves all the problems with their STI shifting. They don’t say if broken cables inside the lever was one of those problems. But, it wouldn’t surprise me if it made the list.
I hope something here is helpful and you don’t have any more STI cables break. Thanks for the great question!
Readers, it would be interesting and helpful to hear if you’ve had issues with STI cables breaking inside the lever and what you’ve done about it if anything. And please share your theories about why they broke.
Jim Langley is RBR’s Technical Editor. A pro mechanic & cycling writer for more than 40 years, he’s the author of Your Home Bicycle Workshop in the RBR eBookstore. Tune in to Jim’s popular YouTube channel for wheel building & bike repair how-to’s. Jim’s also known for his cycling streak that ended in February 2022 with a total of 10,269 consecutive daily rides (28 years, 1 month and 11 days of never missing a ride). Click to read Jim’s full bio.