Bent mech or hanger?

Trying to figure out why my eldest’s bike’s shifting has gone haywire. It’s 8 speed Box stuff. Gears 8, 7, 6 are perfect. On 5 I can hear it trying to rub against 4. On 4 it’s trying to catch 3 but not jumping up to it when under no load. Shifting to 3 more than half the time it jumps straight past to 2 and doesn’t sound great doing so. And then the next shift gets you 1, when you should still be on 2.

When shifting back down to the smaller sprockets it either jumps past 3 to 4 straight away or after a moment.

I bought some spare mech hangers when CRC closed down but I can’t find them anywhere otherwise I’d just swap it to check.

I have got an XT 11 speed set-up (old mech and shifter, fresh chain and cassette) I can swap in but obviously that’s not a super quick job.

Any ideas what the fault is or how to diagnose it? It’s such a long time since I had problems like this on a bike, I’ve had a run of good luck with gears for a decade odd! Now I’ve written this I feel like it must be the mech but please stop me before I waste a lot of time…

I would recommend buying a hanger alignment tool. Even if they look straight, they can be surprisingly bent. Even a new hanger might not be perfectly straight.

As above, it gives every indication of a bent hanger, no point in swapping stuff over. Stop looking for the spare hangers, they will find you!

Thanks, I will pause for now…

“Stop looking for the spare hangers, they will find you!”

They’re somewhere at work so it’s a much bigger challenge than finding them in the garage!

You can make a hanger alignment tool. IIRC the trick is to use a threaded axle if you have one as it has the correct thread to go in the dropout (????). It’s a long time since I did this though.