The quality of the results of multibody-system simulation (MBS) for loader cranes is strongly influenced by the prescribed motion profiles. If hydraulic cylinder positions are prescribed directly, discontinuities in the signal can cause non-physical acceleration and force peaks. This paper presents a hydraulic subsystem developed to provide the actuation for an existing mechanical multibody-system model. The hydraulic drive system model consists of a proportional directional valve, main and secondary pressure-relief valves, hydraulic lines, and a hydraulic cylinder. The component characteristics are parameterized based on experimental measurements on the investigated valves. The model inputs are the directional-valve spool position, the volumetric flow rate supplied by the pump, the pressure at the tank port and the force acting on the cylinder. Based on these quantities, the resulting cylinder stroke is calculated and compared with the measured stroke to evaluate the accuracy of the motion prediction. After one full stroke the median deviation of the end position was 4.62%.