A pulley assembly (10) is provided for mounting on a rotatable shaft of an agricultural harvester and is operable in a high-speed configuration or a low-speed configuration. The pulley assembly (10) comprise a high-speed pulley (16) with a high-speed running surface (36) for receiving a drive belt (14) when the pulley assembly (10) is in the high-speed configuration and a low-speed pulley (18) with a low-speed running surface (62) for receiving a drive belt (15) when the pulley assembly (10) is in the low-speed configuration. The pulley assembly (10) has three sets of teeth (68, 50, 52) extending from surfaces of the two pulleys (16, 18). In the low-speed configuration, the running surfaces (36, 62) of the low-speed pulley (18) and high-speed pulley (16) are axially aligned and the first set of teeth (68) and the second set of teeth (50) are engaged. In the high-speed configuration, the running surface (36) of the high-speed pulley (16) is exposed for receiving the drive belt (14), while the low-speed pulley (18) is positioned beside the running surface (36) of the high-speed pulley (16), and the first set of teeth (68) and the third set of teeth (52) are engaged. The pulley assembly (10) is configurable between the high- and low-speed configurations by disengagement of the teeth, movement of the low-speed pulley (18) along the central axis, and engagement of the teeth.
