Brake booster with a sensing end of the thrust rod provided with a nib

A moving piston (24) has a front face (26) that acts on primary piston (30) of a master cylinder (14) via a reaction disk (28). A feeler (44) at the front face of the moving piston has at least one stud which engages the reaction disk to provide for proportionality between force transmitted between a control rod (36) of a booster (12) and the force exerted on the primary piston. The feeler is fixed to the control rod and comes in contact with the reaction disk to transmit a reaction force from the master cylinder to the control rod.