Old thumb shifter slips - can it be mended? This bike is over 17 years old and not particularly high quality, but it does not make sense to replace the whole thing over one shifter. So I am looking to repair it if possible. I'm confident with most aspects of maintenance, but I've no idea what goes on inside these things.



When changing 'down' to an easier gear with the thumb, the lever slips and the gears do not change. The lever moves further than is expected, with no resistance. By simultaneously applying lots of upwards pressure with the thumb, you can sometimes get it to shift. Once it does shift, the rear functions happily. I've had no other derallier issues.



There's an allen key fitting on the top, and a screw on the bottom. I have not opened it up, worrying that springs will ping out and all will be lost!



I've no idea if it needs more lubrication... or all the gunk cleaning out. Go tighter... or looser?

Thank you.
These shifters are not really supposed to be repaired. Sometimes contamination interferes with the mechanism and can be cleaned out, but if the ratchets have worn out you just need to replace them.

Shimano makes 8 speed shifters that are compatible with older derailleurs. The current Acera/Altus range includes 3x8 and 2x8 shifters for 2 and 3 front chainrings.

Here's the Shimano range line-up page for Acera/Altus: https://productinfo.shimano.com/#/lc/acera_altus/3x8