Recently mangled rear mech, hanger and slightly bent drop out on a stick.
Bent things back into place and replaced mech with an old 9 speed i had.
I know a 9spd mech shouldn’t work with a 10spd shifter and cassette, but on the stand it works well.
Out riding though and chain is slipping…so now i’m trying to work out if its more likely to be the wrong mech or the alignment causing the problem. Do have a new mech to try, but don’t want to open that if the cause is almost more certainly alignment.
What symptoms would you usually get from a 9/10spd incompatibility, i’d have thought poor shifting but not actually slipping?
cheers
Jim

9 and 10 speed are not compatible. The cable pull ratio is different.

If you compare your 2 mechs you will see that the cable stop on the 10sp is on a lever.

You would be able to set it up so one end of the4 cassette works but you wont be able to drop too many gears before the indexing is sat in between gears.

As Jef says, 9 and 10 speed are not compatible.

Getting nerdy the pitch between the cogs is different, 9 speed is 4.35mm, 10 speed is 3.95mm. So for each click or movement of the cable at the shifter the rear mech moves that amount. One click and it’s not massively out, two clicks and it’s now “more” out. To compound the problem the rear mech is designed to move the required distance based on how much cable has been pulled, via a certain lever amount on the rea mech.

You can get widget bodges to make a 10 speed mech work with a 9 speed shifter, and certain SRAM grip shifters work with Shimano mechs. But it’s all a bodge.

Put the correct mech on after you’ve straightened the hanger and drop out correctly with one of these:

thanks both – i understand the whole 9/10 spd thing not working and a 10spd mech will be going back on there.
But my question is would that alone account for chain slipping under load once you’re actually in a gear?

I think it would. As BBS said, the pitch is different so the mech will be not be moving 3.95mm exactly, which will cause it to slip.

The chain not being centred properly means it will try to climb up the shift ramps or down through the gates. And it’ll skip like no bodies business.

ah, that makes more sense now. not just a case of shifting into place, but not centered and the ramps will be doing their thing as well.
cheers

A bent hanger will also make the chain skip. A little bent normally manifests itself as poor shifting, a bigger bent will the show up as skipping and terrible shifting.

Mech hanger first.