Wednesday, 10 October 2012

Shimano STI Gear Cable Snap

Hi Martin

Had a gear cable snap on me 70 miles into a 100 mile ride - it was the classic Shimano STI snapped off  inside the shifter problem. (Old style but is also common on new shifters) As my bike is less than a year old, just over 3000 miles, it might be worth emphasising the issue with our colleagues. Lots of comments on the Internet, and it definitely is a well known issue, but having been through it myself.

In retrospect, I could have avoided this as I'd noticed the shift going excessively out of adjustment on the C2C a couple of weeks ago. I'd put it down to being on the train and being knocked about but when I got it home and decided to check the alignment there was no problem so the alarm bells should have gone off. Worse, I decided I probably should consider changing the cable but decided to leave it until I was ready for a full service in a few hundred more miles when the chain is due for a change.

Anyway, service advice tips for our members:

1) Give away symptom is that the indexing going significantly out (more than a click or so) after being stable for ages - that is the cable lengthening due to strands snapping in the cable - and sticky changes (that's the strands catching) but the alignment is fine.

2) Usage on mine is that I am a very frequent gear changer - I change gear as soon as my cadence is out of a fairly narrow range - so on a ride I probably will be doing hundreds of changes. This has snapped in 11 months - so less than the annual change suggested.

So a sensible check would be to query with the customer the mileage and style of riding and unless a rider is a low mileage, low changer, change the inner cable on the right hand shifter regardless of apparent condition. Left hand shifter is unlikely to have the same problem. Changing the outer might be optional as it is within the shifter that there is clearly some issue with how the cable routes between the carrier and the cable.

Ian Spencer
Spenny Cycles Ltd

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