Have recently changed my chain (1 ride ago) and now whenever I’m in the smallest chainring at that front and largest sprocket at the rear, i.e steep climbs with chain under tension, the chain keeps trying to jump. I’ve tried adjusting the high/low screws, the angle of dangle screw and the cable tension on the rear mech, checked for bent teeth on cogs and tried shortening the chain by 1 link but nothing has stopped it. I measured the new chain against the old one when I put it on, and link for link they were the same, the old one being about half a link longer overall which I put down to stretching. Not really sure where to go with it now, got a full day planned tomorrow so would be good if I could sort it out.
Chain, Cassette and rear mech are 9speed xtr and cranks/rings are slx.
Cheers for any advice!

Everyone must be as stumped as me!

you will either need to buy a new cassette or put the old chain back on

Ok, why will I need a new cassette?

Jump or slip?

Could well be that you’ve worn the front ring and or cassette to the point where it won’t mesh with a new chain. Do the teeth look a bit like shark fins?

As above if its just for tomorrow chuck your old chain back on

If you fit a new chain and it starts jumping, it’s down to worn sprockets.

Generally speaking you should change front rings, chain and cassette at the same time. If you can put up with the jumping for a while it might wear in?

chances are the chain rings will be ok, more likely the cassette is worn with the chain. change cassette then if it still does it then whatever chain ring its doing it in needs changed as well.
For now put the old chain on.

A chain, cassette and chainrings will all wear together, as the chain links loosen up then the chain effectively gets longer and this causes the cassette and chainring teeth to wear accordingly. If you change one component of that system to a new part then you’re likely to get chain skip issues as the components aren’t aligned as they were before.

Check to make sure you have the right speed chain (different in widths). You might have a worn sprocket and/or chainring (check for sharp teeth). New chains need to bed in as the sideplates are quite sharp to begin with. Once they wear in then it should sit better on the teeth. Check barrel adjuster on the shifter. Check cable stretch. Check the guide jockey wheel (near the cassette) for worn teeth. If all fails, then replace the chain, cassette and chainring.

It’s most likely going to be the cassette that is causing the problem.

The chain and the cassette wear together, so it goes without saying that the two should be changed at the same time.

The chainrings wear at a different rate to the cassette so will probably OK for a while , but eventually they will wear – in my experience the middle ring usually wears first.

Try running two/three chains. Easy if you use a powerlink. Have one [a]chain on the bike, one been cleaned and [c][one ready to fit – rotate them every few rides so [a] becomes which becomes [c] which become[a] etc. It will prolong the life of your drive train no end

As above, cassette.

How long had the other chain been on ?

I had the same problem under power, new cassette and new chain, problem no more.

I didn’t change the front rings and haven’t had to.

Do you have a chain checker? I use fat spanner One as it was £4.99. It lets you know how much it has stretched. If you keep upto it, you can change the chain before it stretches and does any damage.

http://www.parker-international.co.uk/19252/BBB-BTL-51-ChainChecker.html?referrer=froogle&gclid=CIXQnPL9kboCFTLMtAodynEAcQ

Is it sucking on the underneath of the chainset? I.e your chain ring is not letting go?

Is it better in a bigger chain ring? As your granny is the smallest it usually wears the quickest on a mtb. if it does then change the granny cog and see what happens.

My advice is change your chain rings and cassette and buy a chain checker and put this downto eexperience and cut your losses.

Thanks for all the advice guys. Stuck the old chain on for today’s ride and was fine, have always changed chains fairly regularly in some sort of hope it would reduce cassette/chainring wear but guess the cassettes on the way out now. Ah well it’ll make it til end of year and then I’ll switch to 10 speed.