Abstract: A fluid operated system for controlling a brake applicable to a vehicle wheel having a flywheel, driven by an unpowered vehicle wheel, connected to the vehicle brake pedal and adapted to disconnect the flywheel from the unpowered wheel to rotate independent thereof when the brake pedal is operated. Upon vehicle deceleration, the flywheel slides forward in the direction of vehicle movement due to inertia and slidably presses against a brake pad which decelerates the flywheel at a rate proportional to vehicle deceleration. A fluid operated valve having a housing containing spaced fluid inlet, storage and outlet chambers which open onto a concave base of the housing is employed to sense the rotational speed of the flywheel.