Vibration Advice>>

just bought a used 46 inch craftsman tractor. Has big vibration when engaging the blades. I saw the right one was bent, so replaced both with new ones from Sears. Still have a vibration. Mandrel? Old blade was bent pretty impressively....
Can I just change out the spindle or do I need to swap out the whole mandrel assembly, if that is what is causing the vibe...
thoughts guys?