A belly dump trailer has a hopper having a bottom gate and a mobile support frame. The belly dump trailer is supported by wheels which may be in a dual axle configuration. The bottom gate is rotated between an open and closed position to discharge a load of materials within the hopper. The bottom gate is driven by a rotary drive connected to the bottom gate by an over center cam lock formed of pivotally connected link arms. The opening and closing of the bottom gate is driven by a pair of pneumatic linear actuators. The bottom gate may be positioned in between the two axles of the dual axle configuration.