master piston as a reactive force that is sensed by the person operating the brake actuator 33 the fluid transmitted during braking from the master cylinder forcing displacement control piston 20 upward causes the volume of fluid contained in the hydralic loop 7 and in the pump cylinders 17 to be displaced with the result that the pump pistons 16 are driven downward into engagement with the eccentric cams 34 therefore the pump pistons 16 are only in engagement with the eccentric cams 34 during braking while during non braking conditions the pump pistons are retracted into the pump cylinders 17 without causing drag on the shaft 2 fig6 shows two piston pumps e g of the type shown in fig2 or 3 disposed at the end of a motor vehicle axle 2 39 2 34 as is typical in the present art the vehicle axle shaft is seen at 2 39 2 34 fig7 a 90 degree coupling is made by 45 degree bevel gears 35c 35d these gears are mounted in a support framework which is affixed to a back plate 103 of the pumps by means of the respective shafts 102 and coupling gears 35a 35b the driven gear 35a of the hydraulic lock mechanism s is are engaged with the vehicle wheel axle 2 39 2 34 as the wheel axle 2 39 2 34 turns so turns the hydraulic lock mechanism s as the free turning of the hydraulic pumps are restricted in rotation or stopped so also is the vehicle axle and the wheels are slowed or stopped the entire pump arrangement is advantageously constructed as a single fluid filled enclosure or housing that also forms the inlet and outlet portions of the circulating loop as seen.