Yes, the 8 speed freehub will take 8 and 9 and even 10. I have setups in all these configurations. 7s needs a spacer. If the 9s cassette is having "issues" probably the spacer is left in place. Shimano cassettes are TIGHT on the freehub body, so it is often easier to split screwed together cassettes, and slide on the sprockets one at a time.