An auxiliary braking device can be used for wellhead applications having a progressive cavity pump. A housing of the device independently mounts on the pump's existing drive using a mounting member, and an adapter on the housing connects to a rotatable drive shaft of the pump. A hydraulic motor on the housing has a motor shaft mechanically coupled to the adapter by a plurality of gears or the like. A control valve couples to the hydraulic motor and operates to control communication of hydraulic fluid through the hydraulic motor, thereby controlling rotation of the rotatable shaft. A controller and electric sensors can operated the control valve in response to the sensed rotation of the shaft. Alternatively, mechanical mechanisms can operate the control valve in response to the rotation of the drive shaft.