I’ve just replaced my chain and cassette and now the chain is slipping when it’s in 7,8,9&10. It’s only doing it under load, and it appears to be running smoothly the rest of the time.
Any ideas?

Split link connected properly?

Yep

Worn chainrings?

Slipping on the back? The chainrings are fairly old but how would that affect slipping on the cassette?

Jockey wheel bearings have play in them.

If the chainrings are worn into a shark tooth profile a new chain is likely to slip under load. I wouldn’t be able to tell where the chain is slipping just that the cranks suddenly slip round under load. If you use one chaing ring less than the others test in the least worn (big ring if you have triple is unlikely to get as much use off road). If that improves things then chain ring wear is likely.

If it is worn chainrings then put your old chain and cassette back on if you still have them and run into the ground before replacing.

Cable tension…?

Just been having the same issue. Turned out that the rear mech mounting had moved. I loosened the mech mounting bolt, rotated the mech until it made contact with the stop on the hanger, and tightened the bolt. Sorted 😀 Or you might need to adjust the “B” screw on the mech (if it has one).

Thanks guys. The chainrings are slightly worn so it could be that, but I did adjust the b screw acouple of weeks ago so I’ll try that first.