chain slip on new chain and cassette

Just replaced my chain, cassette and middle ring. Out last night and the chain was slipping hourendously but put it down to lots of mud. Now the bike is clean it still does it when on the largest cassettte ring and middle chainring. I haven’t replaced removed anything else shifting in a stand is fine up and down on all rings. Chainline is as it has always been although looks at an angle when viewed from behind, the spacer is on the rear of the cassette and if not would only make it worse The middle ring is fitted the right way round. Any ideas is it worth replacing the jockey wheels?

What parts did you use?

Sram PG990 11-32 cassette Sram PC991 chain shimano M770 XT chainring 32T As I have always used.

Yes change jockey wheels as well

Chain slipping on the big sprocket would be pretty unusual. are you sure it’s not the free hub slipping?

Jockey wheels will make no difference. You can run them with no teeth at all and they still work.

yup jockey wheels…. chain aint too long is it ?

Sure about the middle ring?

Does it only slip on the middle chain ring and largest cassette. Could it be the end stop screw not letting the mech move over far enough? Assuming other gears at the back all work fine that is where I would look for starters.

Very similar thing happened to me last weekend – new chain ring and block – I’d switched from XT to 970 block – and it was skipping terribly up slight inclines on 3 largest cogs.

Had to reset the limit screws and cable tension to fix it – so guessing my indexing was out on worn set / or different tolerance caused an issue – seems fine now – but took 20 unhurried mins to fettle.

Chain length is ok, rechecked chainring it was right, checked indexing, going to check freehub top jockey wheel seems to float on what looks like a shaft from left to right from one side of the cage to the other.

Had the same issue on both my bikes. Complete change, cassettte, chain and chain set. After a few wet, muddy rides everything was OK. This is not a new experience or uncommon ime, comes up regularly on here.
Btw my jockey wheels are totally sh****d and everything works fine so doubt that is a problem.

Everytime ive replaced drive chains it’s always been fine straight away this is just something ive not had before. Freehub is fine. Just readjusted the indexing for the umpteenth time and been for a spin and all seems to be better for now. How much float should ther be in the top jockey wheel?

side to side float on top jockey wheel ( guide jockey ) is normal and allows the chain to self align slightly . may be worth checking the b tension screw if a shimano mech (or the equivalent on other makes) to make sure the upper jockey wheel isn’t touching the cassette on the bigger sprockets and causing skipping/slipping. not sure what spacer you’re talking about on the rear of the cassette? could be so may things and without viewing is difficult to diagnose but probably a fairly simple fix and something you’ve overlooked or maladjusted.

are your chainrings in good nick? if so have you checked that there are no stiff links on the chain?