Rear sprockets "wonky"

[lutonloony]

My assumption was that the OP suggests that the cassette is tight and there is no play and the symptom is that the jump is occurring on one part of the cassette. Therefore what seems to be a wonkey cassette could in fact be a bent/twisted hanger. I guess another option is that the wheel is not straight in the dropouts. However, I think we all need more information from the OP.

Wheel is straight in dropouts, and sits central in frame, jump is regardless of gear selection

 

[lutonloony]

Wish I could post a video as it is do hard to describe, but it is almost like all sprockets are bent, so that as wheel turns 180, there is 3mm movement toward wheel. But if you backpeddling sprockets run straight, not sure how else to put this, huge thanks to all contributions so far, feel sure that with your expertise a solution will be found, thanks yo all

 

[Ajax Bay]

Might the freehub be insufficiently secure, given the effect described only occurs when the cassette/sprocket is under (forward) load.
Is the effect less when the chain is on the largest sprocket?
How about two images (rather than a video) from the rear: one with no load and one with a load on?

 

[lutonloony]

Might the freehub be insufficiently secure, given the effect described only occurs when the cassette/sprocket is under (forward) load.
Is the effect less when the chain is on the largest sprocket?
How about two images (rather than a video) from the rear: one with no load and one with a load on?

Will try and get photos sorted, but free hub being insufficiently secure sounds plausible. So being of small brain what is the solution if it is the problem?

 

[fossyant]

You need to get the wheel out and cassette off the freehub. What make are the wheels ?

 

[fossyant]

If the sprockets run straight when back pedalling and only move on drive, it's likely a freehub problem, or, your axel could be bent.

 

[Bianchi boy]

sounds like wheel bearing worn

 

[Ajax Bay]

Have the hubs got a name on them?

 

[fossyant]

It's either something dead obvious, or the hub is a gonner.

 

[lutonloony]

Can't see any name on hubs, but they have "roller" bearings. Having had another play, thinking it is probably a bearing problem as it feels like there is definite play. Like it needs the cones tightening even though there are none if that makes sense. I assume there is no such thing as standard bearings?
As an aside the gear change is mounted direct to frame so guessing it eliminates that option