I have a persistent problem on my 2005 Giant Trance, nasty grating chain skip. I've replaced chain/cassette/rear mech (chainset is reasonably new and not very worn), but this hasn't fixed it. Seems to do it in any gear.
I'm wondering if it might be skipping around with suspension movement, but it's hard to figure that out. It often makes a nasty clatter when I start pedalling again after a bit of freewheeling over obstacles. I've re-routed the rear mech cable down the down tube and zip tied to the swingarm linkage, that didn't work either.
Interestingly, riding at the weekend it was really bad for a while then after a dose of wet/mud, seemed to get better. Chain too clean???

Having had problems with skipping & invested is a new chainset to little effect lubing the cable cured my problems (as predicted by various of the STW massive).

Things to check –

Is the mech cable too short? Suspension action might be changing gears for you
The freehub might be skipping, not the gears.
General gear adjustment, gunky cables, that sort of thing
Stiff/damaged chain links
Is the cassette lockring tight enough?
Are the rear wheel bearings worn?
Are the chainring bolts tight?

🙂

Cheers! That's a whole load of things I've missed then. Time for a quality hour in the garage.

Bent mech hanger? That's caused similar problems for me in the past

Your description does sound a bit more like freewheel issues though 🙂

It often makes a nasty clatter when I start pedalling again after a bit of freewheeling over obstacles.

sounds like a failing freehub – not freewheeling enough thus creating slack in the chain. Could be skipping in the freehub as well perhaps.

Just a thought

two good lists!!
recent versions of this on bikes I have checked have been
freehub
sticky cable
bent mech hanger
typically in the past the stiff links
and bent mech arms/bolts have been culprits

Having said all this it amazes me how much can be screwed and it works fine and to counter that how a little thing (on Sat a small – could hardly see stick- deep in between the cogs on Ben's new Marin) can stop it working

Alternatively a SS will just keep going 😀

bent mech hanger

Ohhhh yes. That's a good point. Bent hangers cause all sorts of niggly little mystery problems..! 🙂