dependent on the input from your pto from the trans, indication of flow direction and suction and discharge of the oil lines, this pump is likely bidirectional , but realistically is designed for one direction. figure out the input direction and note that the flow of gear pumps on the suction side will flow around the periphery or outside of the pump, in other words if when looking at the gears from the suction side of the pump, they should be rotating so as to draw the oil around the outside of the housing , or think of it as the gear teeth separating from each other as you see them. usually the suction side of the pump has larger ports, so if the bigger port is the suction, and when you rotate the pump input in the direction of your shaft from the trans, and the gear teeth are not separating, then you need to use the other input shaft of the pump to change the direction of flow in the pump...