Vehicle wheel speed sensors

A vehicle axle (10), has a casing (II), a central differential (12) which drives outer wheel hubs (13) via respective final reduction gears (15), and drive shafts (14) housed within the axle casing. The axle casing supports at least one wheel speed sensing device (18.19) on the differential side of the associated reduction gear. Each wheel speed sensing device comprises a toothed formation (18) carried by or formed on the associated drive shaft (14) to rotate therewith and a magnetic field effect sensor supported on the axle casing(II) adjacent the toothed formation to provide an output signal which varies in dependence with speed of rotation of the drive shaft and hence the associated wheel hub (13). An output cable (22) leads from the sensor (19) to an output aperture (24) in the casing via an internal passage (23) and the sensor (19) is mounted in a support aperture (11a) in a support chamber (26) of the axle casing. The sensor is protected in the support chamber (26) by a cap (27) which closes-off the chamber.