9-peed casssette wobble

[PJ520]

I've just put a new SRAM 11-32 9 speed cassette on my Trek 520 and I notice that when the back wheel is spinning with no load i.e. on the stand there is a noticeable wobble in the cassette. Is my freehub shot? If so how do I check it? There doesn't appear to be any play in the cassette when the wheel is stationary. I tightened the lockring to 30 lb ft (approx 40Nm) per the etching on the lockring.

There's also a problem that I suspect this wobble is causing. When I am on the smallest front ring and shift up from the 32 to the next ring, 28, (bar end shifters) the chain wants to climb back onto the 32 cog. If I go up another cog and then back to the 28 it behaves OK. On the middle and big rings this climb back problem does not occur. So I'm pretty sure the adjustment is correct. I've got 51K on my old tank and in the past I've changed cassettes out without problems. All the preceding is while on the stand I haven't tried it on the road yet. The SRAM chain has perhaps 100 miles on it so I don't think chain wear is an issue.

I can't find any thing on this site that addresses this issue but I have found another forum where people suggest that this is a symptom of a bent axle. Some time ago I came off quite hard and bent my derailer hanger. I took it into my LBS to get the hanger fixed and everything seemed OK afterwards, could I have bent the axle in this crash?

Is there a spacer or something I could have left out?

[PJ520]

I think I've fixed the jumping gears problem. It was a sticky cable. I slid the outer cable at the derailer as far forward as I could and soused the inner cable in Boeshield. Now it seems to be shifting OK in both directions. But the question remains, what's causing the wobble and is it anything to get excited about?

[531colin]

The only possible cause for the wobble is that the parts which are rotating on each other are less than perfectly concentric/aligned....that is the hub rotating about the axle, the freehub body rotating inside its cassette carrier. A bent axle can't wobble the cassette, a mis-alignment of the freehub body where it bolts onto the hub can.....Unless the freehub body is loose on the hub, I would forget it.
(historical note....in the days of multiple freewheel blocks, this could sometimes be fixed by putting a thin shim before the block on the hub.....the block then has a different position relative to the hub thread, and the errors might cancel......or add up and make it worse!)

EDIT....I had assumed you meant "freewheeling"......if you mean "pedalling" ignore me!

[Brucey]

assuming your freehub bearings don't have play in them as you say (and BTW a bent axle cannot per se cause this) I can think of two things that might cause what you are seeing;

1) an optical illusion; the tops of the teeth are chamfered as an aid to shifting; on some cassettes half are chamfered one way and half the other, When the cassette is new and shiny it looks for all the world as if the sprockets are not running true as they turn. Once the tops of the teeth are covered in crud the illusion disappears to a great extent.

2) its real; SRAM cassettes often have a single screw that holds all the sprockets together. At two other locations there are plastic spigots that locate the sprockets to one another. If the head of the single screw fouls something or the plastic spigots come out of engagement somehow the cassette might actually install such that it doesn't run true.

cheers