A solid bowl screw centrifuge for processing drilling muds includes a rotatable drum and a rotatable screw. The centrifuge has a drive device for driving the drum and the screw with a drive motor as well as a gear assembly for producing a differential rotational speed between the drum and the screw when the centrifuge is in operation. A gear input shaft of the gear assembly is rotationally fixed by an overload lever arm that can be triggered in the event of a torque overload. The overload lever arm is directly and detachably connected with one end thereof and at a radial distance from the rotation axis of the gear input shaft to the gear input shaft or to a part that is connected thereto in a rotationally fixed manner. A method is provided for monitoring the torque on the gear input shaft.