I'm still learning how to maintain my bikes & I'm afraid that this one is a bit beyond me. Any advice much appreciated thanks.

When I change my rear gear down from the top on a 9 speed Deore LX (middle cog at front), the first click has no iimpact at all. Subsequent clicks cause the chain to change normally, until it gets to the lower end & then one click causes the chain to jump two cogs. It's always the same two, 2nd & third largest. The same happens in reverse when I change up.

Adjusting the barrel doesn't appear to have any impact on this. The same pattern occurs whether the chain's trying to jump two cogs, or is reluctant to change 1.

I did change chains recently however (again Shimano LX for 27 speed). Could it be the chain length causing this? I removed one link from the new chain & fitted a powerlink.

Or something else?

Any advice much appreciated thanks, or else it's a trip to the local bike shop.

It's unlikely to be a chain-related issue; rather more likely to be to do with the mech and cable setup.

First thing is to set up the rear mech properly. There should be guides on the internet, but you'll want to adjust the top limit screw, bottom limit screw and b-tension screw (should be a 5-minute job for those). Then you try running through the sprockets (ie rear cogs), and adjust the cable a little if necessary to make sure that enough's being pulled to make each shift happen.

It sounds complicated, and the first time you look at the explanation it may look it, but after after a few goes it'll seem easier. It's the kind of thing that may need readjusting every couple of months depending on the kind of riding you're doing, whether the cables have stretched, etc etc.

have a look on the park tool website – lots of detailed fettling advice on there.

Thank you for the advice guys.

Limit screws seem fine, i.e. the chain doesn't fall off at top or bottom.

B-tension screw (barrel?) doesn't seem to have any impact, therefore I'll investigate the cable.

Thanks again.

One of the best pieces of advice which helped me massively to do the jobs correctly first time was to do it all with the chain off, set it all up by line of sight (ie top jockey wheel with sprockets/cogs), then put the chain on and fine tune.

IIRC you also set up the indexing on the 2nd smallest sprocket so that the chain is just skipping changing up to the next largest sprocket, then screw the barrel adjuster in a half turn.