P-man is right-on the money on this one. Did your dad just put a new belt on because belt deflection shouldn't change drastically by its self. Had a primary clutch spring break before which could also cause this.
Theres one other thing you might want to check, pull the clutch apart and see if the brass bushing s are ok. I've had them work they'reway out and jam up, causing them to act similar to what you are describing. Good luck.
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