Cassette Change Index issue

woolwich

I just did a direct swop from a 12-25 cassette to a new 11-28, as I am going touring and needed the low gear.
I also fitted a new chain by the usual method of big sprocket to big sprocket and add a couple of links.
Nothing else has changed and the gear change worked sweetly beforehand.

The gear change is slick and noise free in all ratios except the smallest.I am experiencing some noise/chattering, as if the indexing is out and it is trying to change gear, only in the 11t sprocket. It does this even with the cable disconnected.
I have adjusted the stop screw through a range of motion. The chain appears/sounds, as it is either wants to change up, (normal) or move down towards the frame (normal) but there is no noise free sweet spot in the middle.

I have adjusted the top jockey wheel through a range a motion all the way up and down but to no avail.

The hanger appears to be perfectly true.

The groupset is a bit of a parts bin special but worked perfectly beforehand. Deore long cage rear mech, FSA crank, tiagra 9 levers, all 9 speed.

Thoughts on what to try next much appreciated.

nicklouse

which lock ring did you use?

woolwich

I used the new one supplied with the new cassette. Should I try the old one? Assuming they are compatible? What are the differences?

Thanks for your input

nicklouse

Mmm nope. the 12T can be bigger in diameter which can cause the chain to not sit on the cog correctly.

check that the chain is sitting correctly in the cog and nothing is stopping it seat.

woolwich

Sorted. Thanks for pointing me in the right direction.
The chain was indeed not seated 100% on the 11t sprocket as it fouled on the new lockwasher. Only by a fraction but enough.
I looked at some other bikes and old spares and noticed that older lockwashers are labelled with a minimum sprocket size. The new lockwasher simply stated "Shimano Hypergide 9 speed" with no further info. I wonder if either they have tried to cut costs by using a generic part or have screwed the manufacturing tolerances up a tiny amount?

Whatever, ten minutes of swopping a couple of bits around and problem solved. Cheers