In a combine harvester comprising a threshing rotor and an internal chopper or beater behind the threshing rotor feeding into a rear straw chopper and spreader through a distribution chamber there is provided a distribution assembly mounted rearwardly of the internal chopper or beater for controlling distribution of the materials transversely of the distribution chamber. The distribution assembly includes a pair of rearwardly extending fins which are moved by a control system for operating the fins to change the distribution at the rear of the combine harvester. The fins are carried on a mounting which is translated side to side and the fins are curved in a direction longitudinally of the direction of movement of the material from the discharge. The fins are controlled in response to a plurality of sensors at spaced positions across the distribution chamber and the sensors measure crop flow at the sensor by detecting impact of crop material on the sensor.
