dosconnected drive on Flymo Hover-vac ?

I've got a Flymo HV2800 which has worked OK for 3 years now. Last weekend the connection between the motor and the impeller/cutter seems to have broken. It looks as though the motor is directly connected to the impeller without a belt or reduction gearing to break. However the motor will run to high revs and although the impeller turns it is not driven by the motor ! Can anyone suggest what may have broken ?