Shimano Acera 8 speed shifter "slipping" on up shifts

[Mububban]

My wife rides her bike for one week a year, and otherwise it hangs vertically on the wall in the garage under a dust cover. It's over 10 years old so it's not the latest version of 8 speed.

The right hand thumb shifter has started sometimes "slipping" and not engaging to shift up into an easier gear. The finger shifter to go faster seems 100% reliable, and the thumb shifter is over 85% reliable. But sometimes it just seems to slip past the point where it normally grabs, and I haven't yet been able to figure out why it slips sometimes. I can't identify what sets it off. Which is annoying as where we holiday every year is very undulating, and shifting is a must.

Is this a common problem with 8 speed? Anyone got any tips or things to look/listen for?

We're on holiday right now so I don't have access to a home full of tools, apart from a multi-tool and set of allen keys. There might be a mechanic at the bike rental place but no idea if they repair non-hire bikes.

[Duck!]

Very common problem with infrequently-used shifters, not anything specific to 8-sp. The grease on the pusher pawl goes gummy, and then the very fine spring doesn't have the strength to pull the pawl into the next slot, so the lever just swings past.

In about the only instance I'd suggest using WD40, although any lightweight lube will do, spray a generous quantity into the shifter so it can soften the gummy grease & allow the pawl to move. Work the shifter back & forward to work the lube in, and all of a sudden the pawl will drop into place and pick up all gears. If the grease is particularly gooey, you may need to remove the bottom cover to gain access to the internals, and use a small flat-blade screwdriver to lever the pawl back & forward to encourage it to free up.

[Mububban]

Very common problem with infrequently-used shifters, not anything specific to 8-sp. The grease on the pusher pawl goes gummy, and then the very fine spring doesn't have the strength to pull the pawl into the next slot, so the lever just swings past.

In about the only instance I'd suggest using WD40, although any lightweight lube will do, spray a generous quantity into the shifter so it can soften the gummy grease & allow the pawl to move. Work the shifter back & forward to work the lube in, and all of a sudden the pawl will drop into place and pick up all gears. If the grease is particularly gooey, you may need to remove the bottom cover to gain access to the internals, and use a small flat-blade screwdriver to lever the pawl back & forward to encourage it to free up.

Thankyou, you saved my wife's legs from exploding on the hills here The local store had some WD40, I gave the shifter a thorough spraying and it was all good on today's undulating 16km ride, with no slipped shifts at all.