The invention relates to a turning gear drive system. A clutch assembly (12) for a turning gear includes an overspeed clutch, an output shaft (48), and a centrifugal clutch (42). The overspeed clutch is disposed at the input shaft (32). The output shaft (48) is in mechanical communication with the input shaft (32) via the overspeed clutch. The centrifugal clutch (42) is disposed at a portion of the output shaft (48).