Grass catcher problem

[Rich A.]

So I have a 42 fabricated mower deck with the turbo blower grass collector. For the last 2 seasons i cannot keep the belt on. Looks like it is vibrating and throws it off the pulleys within minutes. I've changed belts and made several adjustments but nothing works. What am I missing? And can I use the standard grass collection system or do i really need the blower? Thanks!