Periodically I’ve felt a slight ‘kick’ from my drivetrain when pedalling but haven’t really paid it much attention (it feels a bit like a stiff chain link).

Today I got caught out in heavy rain for sometime so presumably lost most of my lube; the ‘kick’ (felt through the pedals) was much more noticeable.

If only occurs when I’m using the 4th smallest cog (third up from the smallest) in any chainring (I’m still 3×9) and no other.

I can find no movement from the cog and the whole cassette seems fine (there’s also no scoring on my famously soft aluminium Hope freehub which I would have expected if there was any movement at all). I’ve removed and retighten the cassette and can see no worn or broken teeth on the cog.

The cassette (SRAM 980) and chain (KMC) are reasonable new and were fitted together.

The 980 cassette comes in 4 pieces (excluding the lock ring) with the 1st and 2nd cogs separate, a block of 4 cogs and a block of 3. The problem cog is the second on the block of 4 and can’t move independently of other cogs on the block.

There’s no clearance issues of contact between the cassette, chain and rear mech and I can find no reason for the issue so I was wondering if anyone had any ideas?

I suppose that a new cassette might solve it but there doesn’t seem to be any wear on the one I have.

Slipping pawl in the freehub itself? Quick and easy to replace on Hope hubs…

Could it be your pedals?

I suppose that it could be all sorts of things (it feels very similar to a kick I once felt when one of the cartridges in my rear hub started to fail) but I have no idea why it only occurs when riding a single, specific cog; every other cog (including those either side) give a perfectly smooth ride.

How new are the chainrings? 3×9 it could be that the kick is the chain picking up on one of the pins on the rings due to the specific chainline..

The chainrings are fairly new (although they’re on ancient XT Octalink cranks). The granny and middle ring are steel 9 speed Deores (which I’ve used before) and the outer ring is a 9 speed SLX.

I did have an issue years ago with the chain catching on a shifting pin on a silly thick Middleburn Hardcoat outer ring, but again, I get the kick in all of the chain rings (whilst riding the 4th cog), even the outer which doesn’t have any pins to the right to catch on.

I don’t think that it’s a major problem, it’s just starting to annoy me!

My guess is a slight misalignment in the rear mech hanger.

I’ve had this a couple of times, you can adjust it out but it occasionally tries to shift a little in some gears.

Carefully realign or fit a new hanger, and see if that helps.

Also worth checking chain – I had very similar, and it took me 200mi to discover i’d been riding round with pin half falling out of a chain link.

My guess is a slight misalignment in the rear mech hanger.

I’d go with that too.
Get the bike in a stand put it in the offending gear and get someone to turn the crank slowly while you watch what the chain does at the cassette.
Bet it’s slightly catching a shift ramp and trying to change gear.
I’ve previously had the same problem and a quick tweek of the gear hanger always solved it.

Thanks for the thoughts, I’ll have another look and see if I can work out what’s going on.

If you have no luck finding anything, feel free to pop into the shop on Saturday and i’ll take a quick look at it for you.