The bottom jockey wheel (10 spd Zee) on my mech has worn so much it’s more or less just a disc. I have an old Zee mech that I can pilfer one from but it’s the top one.

Are they different or can I swap with impunity?

Don’t know about Zee, but most shimano mechs have a different upper wheel with a little bit of play in it to help shifting.
Can’t see why it wouldn’t work though.

You’ll not die, at least not as a result of swapping jockey wheels, but I’d be pretty sure the shifting will be sloppy. By all means give it a try but be prepared to buy proper ones if it doesn’t work well.

You will be fine. I doubt that you will even be notice any difference from the proper replacement.

Hmm. Tried it today and there’s a horrid rattling noise coming from the back under load, but shifting fine… Need to have a poke around and see what’s causing it.

Sounds like it’s time for a new bike. 😀

Is the chain routed through the mech correctly?

Ha it is… But I did that exact thing on the commuter the other week.

Sorted 🙂

You can pick up replacement jockey wheels for a few quid. Or pay a little more (around 15-30) for some bling shiny ones. Very easy to replace too.

I don’t think you will die if you don’t though.