A hydraulic power output unit can be used in a hydraulic hybrid drive system for propelling a vehicle. The hydraulic power output unit includes a housing having an input shaft that extends within the housing and is adapted to be rotatably driven by a source of rotational power. A hydraulic pump is rotatably driven by the input driveshaft to pump hydraulic fluid. A vibration damper is provided within the housing for dampening vibrations in the input shaft.