Abstract: A drive assembly brake is mounted in the gearbox connecting a motor driven input shaft to an output shaft, the output shaft being connected by a tubing string to a submersed rotary pump. The gearbox includes an output shaft housing portion defining an oil chamber and an input shaft housing portion defining an oil-free centrifugal brake chamber. The relatively faster moving input shaft carries a centrifugal brake having weight members frictionally engageable with the brake chamber wall when the rotational speed of the input shaft reaches a sufficiently high degree, and the resulting braking action retards the rotation of the input shaft.In one embodiment a split casing gearbox is used having matched passage portions in the faces of the connected gearbox portions to form a lubrication passage system for the shaft bearings.