Well it just happened again, this time after 13 months and about 3000 miles. This time the unit was totally jammed. I removed it from the handlebars and rapped it a bunch while holding it in various positions. It finally started to "shift" but this time the cable fragment was no longer seated in its socket and was badly jammed way underneath. It took about an hour of shaking, shifting and probing with tweezers and wires to get it out.
Unlike older shifters which had a drilled hole where the cable sits in its socket, this 10-speed shifter has a notch. This makes it much easier for the broken end to fall out and jam the mechanism. Thanks, Shimano.
Both cables were genuine Shimano. Perhaps some other brand will last longer.
(In the process, I tried to remove the combined main shift lever and outer shell to get at the loose end. I got as far as a small Phillips head screw underneath the lever with a locking plate. Even with the locking plate disabled I was not able to loosen the screw.)
- Replace the rear shift cable every 2000 miles and the front every 4000.
- If the cable breaks, try to resist repeated clicking of the shift lever, which just rotates the loose end to the bottom where it will fall out.
- If the cable breaks, try to get the loose piece (cable end and nipple) out of the shift lever immediately. Riding the bike is likely to jar it loose.
- If the shifter is jammed after a broken cable, try inverting the bike and then shaking it or tapping the shifter with something like a screwdriver handle.