A vehicle brake has a fixed backplate (1) carrying a pair of friction elements (2, 3) and an actuator operable to urge the elements into braking engagement with a rotary braking surface. An abutment (5) for the elements (2, 3) has a portion (10A) which is deflectable by load on the elements arising from braking torque. A radiation input means (10) directs radiation at a surface (11A) of the deflectable portion (10A) and means are provided to sense radiation after its impingement on said portion and transmit the sensed radiation to means (14) producing a responsive electrical output representing deflections of said portion.