Right so long story short. I replaced the jockey wheels on my rear mech, xtr m970, a little over a month ago. Had some trouble with the indexing at the time. It threw it way off. So at the time i didn't really have the time, or to be perfectly frank the inclination, to get it perfect so i got it to a near enough point & left it be to be sorted at a later date. Cue this evening, said later date, I've a nice new bike repair stand so i figure i'll sort out said issues with the rear mech as they're starting to piss me off. After the best part of 3/4's of an hour of pricking about with it i still can't get it to index right.

I've reset the cable tension. I've adjusted the B-tension screw. I've played with the micro adjust. I've adjusted the tension on the top jockey wheel. Yet it still refuses to index. When i get it indexing perfectly up it's way off on the way down & visa versa. Now i can only surmise it's down to the new jockey wheels which i replaced. However i can't help but wonder whether i've missed something hence the fact i'm asking on here. So anyone able to point out anything i might have missed? That is before I resort to looking for new jockey wheels.

Bent mech hanger.

You get bottom or top of cassette but never both.

it may look bang on but whack a gauge on it and check for sure.

Replace existing outer and inner cable with new. It's probably kinked somewhere.

I've no reason to believe the mech hangar is bent. Shifting was ok before replacing the jockey wheels. Cables could be it, though they're gore ride-on cables & haven't given me any trouble up till now so i'm hoping not.

I've got similar issues at present and the mech hangers been checked.

Assuming B tension, hi / lo set screws, mech hanger and chain length are all ok some thoughts:

Have you
got the cable routed on to the correct side of the pinch bolt on the mech?

tightened or slackened the loop of cable entering the mech or introduced tight bends elsewhere?

taken the cable out of the mech, held the cable between your fingers and checked how easily the inner indexes back and forth?

tried turning the cranks and moving the mech by hand?

If everything incl mech hanger and mech is ok and the cable is sliding freely it's possible it could be a malfunction with the indexing in the shifter itself. Not seeing any correlation between the new jockey wheels and the problem. If all else fails borrow another shifter and or mech that does work and see if you can get it to work on your set up – process of elimination…

got the wheels right way up? no really, there's a top one and a bottom one…

What bassspine said