Abstract: Paper drive unit instability that includes a variable displacement hydraulic motor (34), a rotary output (48), and a displacement controlling wobbler (36, 40) in the case of an aiding load can be avoided through the use of a double acting hydraulic actuator (42, 44) connected to the wobbler (36, 40) along with a control valve (30) including a single spool (80) connected to the motor (34), and wobbler control pilot valve (62) and to the actuator (42, 44) for a) controlling the speed and direction of rotation of the motor output (48); and b) controlling the actuator (42, 44) to maintain minimum displacement of the motor 34 when an aiding load occurs. System optimization can be achieved by changing the differential pressure setting in response to the available system pressure.