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Torsional vibrations of an engine-powered hydraulic system were analyzed. The system consisted of: a diesel engine, spline shaft with clearance, universal joints, propeller shaft, mechanical transmission with clutch engagement, hydraulic pump, and a load. Excessive torsional vibrations resulted in propeller, spline shaft, and U-joint failures. Although the system had been adequately designed for the steady-state horsepower requirements of the pump, field failures began to occur after several systems were built and delivered. A nonlinear dynamic analysis was performed, which included variations in system parameters. The analysis revealed that two design changes would reduce the dynamic stresses. These were to increase spline clearance and to add a torsional damper to the propeller shaft.