A braking system for a rotating chopper drum (14) of a forage harvester (10) driven from an engine (11) via a drive train including a disengageable clutch (21). The drive train also drives a first pump (28) connected with the drum (14) which pumps fluid around a hydraulic circuit which includes an openable restriction (40). The system is arranged to brake the chopper drum (14) by disengaging the clutch (21) and arranging the first pump (28) to pump fluid around the circuit via the openable restriction (40) as the drum (14) continues to rotate to convert the energy of the rotating drum (14) into heat.
