Deore M590 to M772 XT indexing problem

dashton

Hi,
I have just swapped my Deore rear mech for a used M772 XT and the cassette from an unkown sram to a used M770 XT, the shifters are new deore M590 9 speed and used to index perfectly. Now i have to double shift a couple and it sometimes slips under load.
I don't know if the indexing is slightly different (so i need an xt shifter) or i need a new chain but it was ok before. The mech looks straight (but i will strip it and check) and the cassette is good too. I have tried swapping the cassette back but the problem remains so chain or mech??
Any ideas appreciated...
(Bike is a Trek Fuel 70 with Shimano deore crank)
Cheers
Dean

cooldad

Used mechs are ok, but why buy a used cassette?
The chain is probably nicely stretched to fit the previous stuff nicely, so if you are sure you've indexed correctly, then new chain. Maybe.
If it still doesn't work with the old cassette I'd say you haven't indexed properly though.

Chunkers1980

Cables? Mech screwed in correctly?

When you say changed back do you mean the cassette too? Chains mesh with cassettes over time and left long enough will slip.

dashton

Thanks guys,
I'll try and get a chain tomorrow and check the mech while its off.

Chunkers1980

A new chain isn't going to help on an old cassette

The Rookie

No but a new chain may well help on a nearly new cassette where the old chain is stretched to oblivion!

dashton

As above, cassette is only lightly used. New chain seems to be much better once there is a load on it (still not perfect on a stand), have a ride tonight so fingers crossed.
Cheers