effect actuation of the mechanism 14 in response to application of an operator applied force in the direction of the arrow f in fig1 against the clutch pedal 12 the piston and cylinder units 16 18 are operatively associated with a hydraulic fluid reservoir 20 and are connected by means of a fluid circuit 22 consisting of a first conduit 24 fluid communicating the reservoir 20 with the piston and cylinder unit 16 and a second fluid conduit 26 operatively connecting the units 16 and 18 as best seen in fig1 the clutch pedal 12 incorporates a foot engaging portion 28 and is pivotally connected to a suitable fixed portion 30 of the associated vehicle by means of a suitable pivot pin or hinge arrangement 32 the pedal 12 is provided with a return spring 34 that functions to cause the pedal 12 to be automatically biased to its normal deactuated position at such time as the pressure in the direction of the arrow f against the foot engaging portion 28 is decreased or relieved the piston and cylinder unit 18 is operatively associated with a suitable actuating linkage 36 that is pivotally connected to a suitable fixed portion 38 of the vehicle by means of a pivot pin or the like 40 additionally a return spring 42 is associated with the linkage 36 for causing the linkage 36 to be biased or pivoted about the axis of the pin 40 in a direction opposite that shown by the arrow a in fig1 as will be described in detail at such time as the clutch pedal 12 is depressed or is pivoted in a clockwise direction in fig1 the piston and cylinder unit.