A bearing failure detector for an electrical generator includes a disc located within the bearing assembly near the location of the main bearings. The disc includes an electrically conductive ring encased in an insulation layer. The ring is exposed along inside diameter of the detector disc adjacent to the periphery of the shaft, but the dimensions of the inside diameter of the ring are slightly greater than the normal internal clearance of the main bearings, so that the shaft does not contact the ring unless the bearings are significantly worn. The detector ring is connected to a resistor with a large resistance which is monitored by a control circuit at all times. When the internal clearance of the main bearings has been enlarged by a predetermined amount, the ring contacts the shaft, changing the resistance monitored by the control circuit. This causes the control circuit to provide an indication that the bearings need replacement. The detector eliminates the need for preventive replacement of bearings at scheduled maintenance periods when the bearings may not actually need replacement because they are not sufficiently worn, saving service time and costs. Auxiliary bearings are provided to support the shaft when the shaft has contacted the detector, providing safe operation of the generator for a sufficient period of time after a bearing replacement indication has been provided until the bearing assembly is replaced.