Abstract: A wheel speed sensor for a vehicle adaptive braking system is installed within the vehicle hub cap so that the hub cap and speed sensor assembly are installed on the vehicle wheel as a unit. The speed sensor includes a rotor assembly which is rotatable with the hub cap, and a stator assembly which includes a bearing which slidably and rotatably receives a spindle which is integral with the hub cap. A tang projects from the stator assembly and is received in a corresponding slot on the vehicle axle to prevent relative rotation between the sensor assembly and the axle. A spring is provided which rotates with the hub cap and which yieldably urges the stator into engagement with the end of the vehicle axle. Consequently, the hub cap and sensor assembly are installed and removed from the vehicle as a unit, thereby facilitating installation of the sensor assembly since the air gap between the stator and the rotor may be set at the place of manufacture of the sensor assembly.