Help with loose 8 speed cassette!

Hi guy's, ive just bought a set of stx rc 8 speed wheel's and have converted my Alpinestar's to 8 speed. The problem is that although the gear's are all working ok, it seem's that the main body of the cassette isnt tightening up and you can grab hold of the cassette and rock it in your fingers slightly. It's as if there is a spacer or something missing from the rear (possibly) to bring the cassette forward slightly on the freewheel so as the whole lot tightens up. Hope ive put that across in an understanding way. Any help would be greatly appreciated. Thank's Dave.
PS Still after a new project of some sort, if you have anything interesting, give me a shout!

Loose cassette

What you need,is the thin spacer washer from an old cassette.This usually fits between the end of the main bulk of the casette,and the first loose sprocket.You put this onto the freehub body first,then your cassette,this takes up the slack and allows the cassette to tighten.The reason for this slack is that on older cassettes that had a 12 or 13 tooth bottom sprocket,the splines on the bottom sprocket were cut all the way through the sprocket.On later cassettes,usually with an 11 tooth bottom sprocket,the spline is not cut all the way through the sprocket,and therefore the sprocket somes to a stop on the freehub body,and the rest of the sprockets then move indepedently from the bottom sprocket.Hope this helps,if you try your local shop,you should be able to get this sopacer from a scrap cassette.If notsend me your address and i will send you one.

the freehub body is the same size as a bottom bracket ,so if you have a thin spacer for one of those knocking about thatl do

Cheer's guy's, i thought i was missing a shim of some description. If i have no joy locating one i'll be grateful to take up Mr Grumpy's offer if that's ok. Many thank's Dave.