Variable preload bearing assembly

For supporting a shaft of a spindle, a bearing assembly comprising a pair of bearings with at least one of the bearings having an inner race and an outer race, one of the inner and outer races being mounted for rotation relative to a shaft of a spindle, the other of the inner and outer races being axially displaceable in a direction parallel to the axis of spindle rotation, a pair of race adjustment members, each adjustment member having a threaded section with a pitch different from the pitch of the threaded section of the other adjustment member, a rotatable preload actuator having differential thread portions meshingly engageable with the thread sections of the race adjustment members for adjusting the axial position of said other of the inner and outer bearing races relative to said one thereof, thereby to selectively vary the loading of the bearing, an adjustment control including a bearing load sensing device for determining actual bearing load, and drive means for rotating the preload actuator to control actual bearing load under running conditions by effecting axial positioning of said other of the inner and outer bearing races relative to said one thereof.