Is there anything different to a conventional mech?
Mech is on the bike and I can push it from small to cog to big cog with no chain on.
It is a used 10 speed 786 XT mech and am running it with a XT 9 speed shifter.
With it all connected up the cable will only pull it enough to span 4 cogs. What am I doing wrong?
Everything worked perfect with the previous mech.

Chain too short?

You’ll need a shimano 10spd shifter for it to work.

Need a 10 speed shifter and sounds like your cables either not tense enough, or shot.

Yep different pull ratios. You’ll need a 10 speed shifter and 10 speed casette. Like wot Simon said.

Ok will fit it to my 10 speeder.
Is there a clutch mech for 9 speed?

Is there a clutch mech for 9 speed?

No

Ok will fit it to my 10 speeder.
Is there a clutch mech for 9 speed?

No

Not totally true – Sram shifter will work 9 spd with Shimano mech with a bit of fettling.
Or you can use a thumbshifter on friction. This works suprisingly well, I’m currently using a 9spd thumbshifter on friction, with an SLX Shadow+ 10spd mech, on an 11-28 8spd cassette. Works really well!