Hello. Randomly in the middle of a ride the other night my chain started slipping but only in the smallest cog at the back. All my drive chain components are brand new, I changed the cassette, the chainrings and the chain just 3 weeks ago, they’re allXT except the chain which is KMC. The set-up is fine, one click on the shifter takes the gears up one cog and the same back down. I checked the chain thoroughly and none of the links are stiff. I had the lock ring off and taken off and put back the top two cogs, in case they weren’t fitted correctly or if the lock ring was loose. I’ve messed about with the b screw and in or out a little bit makes no difference it still jumps. It does it while in any of the 3 chainrings so not limited to one or the other. The only thing I can think is that I might have bashed the mech on a log perhaps but the mech on the hanger looks straight and it doesn’t skip in any other cog but the smallest.
Help me Obi wan Stw, you’re my only hope. I like to go fast!

Try undoing the limit screw one quarter of a turn at a time; also make sure there’s not too much tension in the cable as to prevent the derailleur from reaching its limit screw.

As above, put it in top gear (smallest sprocket) and then wind the barrel adjuster right in so the cable is properly slack and the mech is sitting on its limit adjuster. Does it still skip? You might be right though and have slightly bent the mech hanger – the smallest gear does tend to show issues first just because the jockey wheel is at its closest. Have you checked for a damaged tooth on the sprocket?

Probably a very slightly bent hanger then.

Your lbs has a tool to check this.

Unlikely option a damaged tooth on the small ring.

Also check the cable runs freely and does not have a small kink at the derailleur end – that can stop the derailleur positioning properly but still feel ok.

Did you change the cassette for a same ratio one? Only reason is that I had this once where I’d used a 12T lockring on an 11T cassette and the flange (fnarr!) of the lockring was slightly proud of the cog.

Did you change the cassette for a same ratio one? Only reason is that I had this once where I’d used a 12T lockring on an 11T cassette and the flange (fnarr!) of the lockring was slightly proud of the cog.

this. outwitted me for ages that one.

B screw? Is the jockey wheel fouling on the cassette?

APF

Cheers lad, I’ll have a closer look at the cog and have a mess about. I used the lock ring that was supplied with the cassette so I can rule that out at least. Looking to go to Cannock tonight so chances are I won’t need the smallest cog.

lcokring and limit screws most likely, B tension screw then bent hanger least.

I had a cassette that did this, replaced it and all OK.

I used the lock ring that was supplied with the cassette so I can rule that out at least

assuming of course the right one came with it. Worth checking, I’d say, given it’ll take 30s.

I’ve been having the same problem. Had a really close look at the cassette as turning peals. One of the teeth on the 13t cog was catching the chain and flicking it slightly. Quick dunt with a hammer and drift and it seems to be cured.
Be out tomorrow for a ride so will know then if its properly sorted.

Is lock ring fully tight?

I was about to ask where you are Jekkyl, but spotted you’re a Cannock local??? So too far to pop round and use this:

I bought one years ago. The one piece of kit that has saved me loads of grief.

I had this and it turned out to be the chain connector link. It was on a wipperman black 10speed chain and their easy link is a sort of jelly bean shape…turned out it didn’t like the 11t sprocket…OK on a 12t but not 11t. I changed the connector to a sram power link and all good!