A rotational speed control device includes a housing containing a viscous fluid, a shaft disposed in the housing and rotatable relative to the housing, a hub assembly secured to the shaft for rotation with the shaft, and a rotor coupled with the shaft by a frictional engagement with the hub assembly. A spring is disposed in the housing and acts on the rotor to bias the rotor axially on the shaft in a low torque direction. A braking torque between the rotor and the housing is varied according to an axial position of the rotor on the shaft.