The lock ring for the cassette is probably not on flat. It’s possibly rubbing on the stays. Take the lock ring off, put it back on, with some downward pressure on it, and check it’s located properly in the freehub threads.
Thanks everyone, going to have a look shortly. If it is a sticky freehub, will a thorough clean do or does it mean replacement?
SRAM are the same take it off give a good clean. I managed it so it 's not a hard jobDepends on the hub. If it's a shimano hub I'd be tempted to take it off, flush it through with WD40 or another light solvent based lubricant until it spins freely and then relubricate it thoroughly. Worst case scenario it doesn't fix it and you replace the freehub body.
For other hub manufacturers this may not be possible, I don't really know. From memory Park Tool has a very good page on how to service a freehub, google should find it for you.
Yep, definitely check that first!Hopefully it’s just a wonky lock ring, or some crud in between the ring and the stays, in which case there’s not much to do.
That’s the problem. The lock ring isn’t in straight, so you can’t tighten it up enough to stop the sprockets being loose, and it will be fouling the stays as it rotates, causing the snatching. You have to press down on the lockring as you tighten it, to ensure it goes in straight. I use the palm of my hand pressed down quite hard onto the lock ring, for the first couple of turns, then use the lockring tool to tighten it all the way up.This might be a coincidence, but as near the suggested area of concern might be a factor. Took the wheel off and noticed the sprockets are loose, as if I'm missing a 1.5mm/wtvr spacer twixt the smallest one and the lockring. Would that be enough to cause the snatching?
Sounds like you have a combination of not having a spacer on the spoke side of the cassette which means the lockring can't be tightened properly thus (possibly) causing the snatching referred to by rr above. If, with the (correct dimension) spacer in and the lockring properly installed (to 40Nm), the chain fouls the stay when on the smallest sprocket/large chain ring then the wheel may have been set up on the hub too close to the axle end on the right (drive) side. Your LBS will be able to sort this fairly easily, if you can't.There is no spacer on the spoke side, but I have found the one that should have been there (long story).
I was thinking of a spacer being needed on the other side as it seems the chain rubs the stay when on smallest cog.