Step One: Ride the bike 5 days a week for a year or so.
Step Two: Change gear roughly 1 million times per ride.
Step Three: When it starts shifting badly between gears 7-8 decide "ah I'll look at it at the weekend"
Step Four: Continue riding it whilst thinking "bugger this is getting worse"
Step Five: Leave it in 6th and limp home because its completely knackered
Steps 3 -5 happened over a period of about one and a half rides, so it was a fairly terminal failure. It didn't feel too bad at first, then all of a sudden I could barely change gear at all so opted to just leave it in 6th (the most all round gear for my ride).
The good news was I could tell it wasn't a problem with the hub. It was clearly the shifter, since it was making some horrible noises and felt like the teeth on the ratchets had mashed themselves to bits from overuse.
This was all no big deal really. I have other bikes to use and to be fair this shifter is not only second hand but has also done a hell of alot of work for me since I change gear so often whilst riding it. Mainly because the 8 speed hub allows you to pick just the right gear for whatever the circumstance, so I tend to go for the correct gear to maintain a steady cadence. Unlike on a deraileur where I might either pedal harder or faster just avoid shifting.
Practical cycles furnished me with a brand new shifter via their eBay site which was a piece of cake to fit.
Once that was on I could have a look at the old one to see what went wrong. My guess at it being the plastic rachety teeth was completely wrong. Turns out it was a teeny tiny spring. I'm not entirely sure where it goes or what this spring does, since it was in two halves and loose inside the case. This had then been mashed against the moving cable, frayed it and then caused the wholse thing to sieze up.
So there you have it. the Shimano shifters are mostly made of plastic, but it was one of the few metal parts that fatigued and broke, taking down the rest of the ship with it.
|Beat up old shifter|
|The result of the frayed cable from all the way up at the handlebars|
|Shiny new shifter with cable already included and ready to fit|
|Shiny new one fitted, works perfectly straight away.|
|The old shifter taken apart - teeth were fine|
|This is the tiny spring which had broken - filthy fingernail for scale|
|This is roughly how it should look when not broken|