Abstract: An agricultural forage box includes an infinitely positionable variable speed drive system and an improved trip mechanism. The variable position drive system utilizes a drive belt for driving the floor conveyor of the forage box, which is driven in response to rotation of a pair of sheave sections. One of the sheave sections can be moved relative to the other, and a sheave positioning mechanism provides adjustment in the position of the movable sheave section. The variable position mechanism includes a yoke which is movable in response to operation of an actuator plate and linkage mechanism, which in turn is interconnected with a control lever. The improved trip mechanism includes a trip bar mounted to the forage box for pivotal movement about its longitudinal axis. A trip lever is located adjacent a declutching tab associated with the power train. A pair of cables extend between the trip bar and the trip lever, and are connected one on either side of the trip bar longitudinal axis.