Hi

I’m planning on replacing the original rear mech on my mid-’90s hardtail.
Will a 9-speed Shimano rear mech (e.g. Deore M591) work ok with the 7-speed cassette/chain set-up?

Any advice appreciated.
Thanks.

I think it should. It did on an 8-speed set-up.

The only possible issue is that the chain might be a bit thick to route thru the mech/jockey wheels properly. I think 8-9 speed chains are pretty much the same width, whereas 7-speeds are a bit thicker. Could be wrong like.

Ok, will give it a go, thanks.

as above – you may find that the plates in the mech are too close together to let the chain through.

what they said ^.

you may be able to boge some washers/ 7sp jockey wheels in the mech. depending on design though… (never tried this)

It’ll be fine. 7/8 speed chains are the same thing. 9 speed are narrower, not sufficiently to cause problems on the mech.