It looks like the ratchet mechanism broke in one of my shifters. As I try to shift the bit holding the end of the cable stays put and does not follow the lever. Even when it moves I can then pull by the cable and it then goes back to its starting position.
Here is a video showing what's happening.
It happened while I was cycling and I was left with only the smallest cog. There was a sound of something breaking and at first I thought the cable snapped. But it could have been the sound of the pawl breaking somewhere inside as I was trying to shift to a larger sprocket.
I was wondering how much work is replacing the mechanism and whether this can be done at all (assuming I can find another shifter to salvage the part from)? Or does the whole shifter need replacing?