My rear mech has been shifting badly so I tried to index it, and in doing so I noticed that the rear cassette is wobbling badly. I have tightened up the lockring as far as I can but can still detect a tiny bit of movement.

Any ideas why this is, or how urgent a problem it is? Are there any simple checks I can do to determine what the exact problem is, do I have to take of the cassette etc?

Further info:

The hub is a Shimano XT six bolt, with an XT cassette. The hub and cassette are both about nine months old. My chain has slipped off the back of the cassette a couple of times recently, which may have subjected the cassette to forces not expected under normal use. The cup/cones seem to be tight, since if I hold the rim wand try to wobble it whilst the wheel is in the frame I detect no movement.

Thanks in advance!

take the cassette off, and it may not be an XT but a cheaper one with a 'screw' to hold it together

I've got an XT hub that does this too. Changing the cassette didn't get rid of the problem, so I think it may be the freehub.

Mine's been doing this for well over a year though and is still more or less functioning, although the play has increased over time.

Freehub loose?

If I take the cassette off and the freehub body wobbles, then its the freehub, yes? And if that is the case can I do anything about it?

@b r – cheaper cassette or cheaper hub? Pretty sure they are both XT, I bought the cassette packaged and everything.

Mine was doing this and it was because the freehub bearings were fecked – on Hope Pro II.

could be last cog or lock ring aint on straight. ive seen that a few times before.

are you sure the cassette doesn't need a spacer on behind it…like one of the ones that goes between the cogs that are separate, but on before even the biggest one. i've had this before.

There are probably two different problems here;

Legs, you have Problem one (my 09 XT had this and almost every other fault from the box); some of the more recent XT rear hubs don't deserve to wear the badge and have a ridiculous ammount of wobble.

Problem two; cheap cassettes sometimes don't fit on the freehub splines tightly enough.

OP – you may have one or both or even a combination, I don't reckon the problem can be down to the chain slipping over the cassette; you just need to make sure you set the limits so it can't or you'll trash spokes.

Mavic wheels?

If so, the cassette needs a spacer [that should have come with the wheel] 2.6mm, I think

Cassettes have always had a slight wobble when spun. Only by about a millimeter or two though. Mine have always done it anyway

Yep, depends what you mean by wobble. I've seen a number of bikes with a side-to-side movement of the cassette as the wheel goes round. There was nothing wrong with them, that's just how they were and I hadn't noticed before. One case was a brand new bike out of the box and I noticed it because I'd seen the same on a friend's bike

If the shifting works, then I wouldn't worry.

I will have a further look later today and report back…

The shifting isn't quite right at the momment, but i'm not sure if that's because the chain is too short(?) on my 1×9 set up, or something to do with the sealed cable set up being rubbish.

Ok I have removed the cassette and it appears that the freehub body wobbles on the rear hub.

Is there anything I can do about this?

Bike currently sat downstairs surrounded by flakes of mud, awaiting attention.

If the freehub body is loose you can tighten it in with a 10mm Allen key BUT, you have to have the axle and bearings out to do this I believe. Also some shimano hubs need a spacer behind the free hub (But that's just deore I think).
So remove axle and bearings and ighten the freehub with a 10 mm allen wrench.

Jay

Ok, tightened freehub but it didn't do anything.

Solution: Ignore, hope for best.

Thanks for your advice everyone.

When you spin the wheel does it look like the spindle is bent or can you physically move the cassette about without the wheel turning?

replace freehub?

How much play? There will always be a small amount from new.