Braking control arrangement for a motor vehicle, comprising a brake pedal capable of actuating a pneumatic brake booster of at least a first master cylinder connected hydraulically to at least a first braking member of the vehicle, the said booster comprising a rigid envelope inside which there can move at least a first transverse partition delimiting in a sealed manner a first front chamber, subjected to a first pressure (P 1), and a first rear chamber, subjected to a second pressure (P 2) varying between the first pressure (P 1) and a pressure (P a) greater than the first pressure (P 1), the said booster comprising a first tubular movable pneumatic piston which is mounted slideably and returned elastically towards the rear inside the envelope via a return spring, of which a front portion is secured to the first movable partition, and which is capable of acting on a rod for actuating a first hydraulic piston sliding in a first hydraulic chamber of the first master cylinder via a reaction disc, the said booster comprising a control rod coupled to the brake pedal and moving in the first pneumatic piston selectively as a function of an axial input force exerted towards the front against a return force, the movements of the said control rod being capable of determining the openings and closings of at least one axial valve, termed "intake" valve, which is interposed between a pressure source subjected to the pressure (P a) greater than the first pressure (P 1) and the first rear chamber, and of at least one axial valve, termed "equalizing" valve, which is interposed between the first front chamber and the first rear chamber, in order to actuate the first movable partition, the said booster comprising a plunger, which is received in the first tubular pneumatic piston, which traverses the first movable partition, which is secured to the end of the control rod, and which is capable of acting directly on the actuating rod of the first master cylinder via the reaction disc in order to transmit to the control rod the reaction force of the hydraulic fluid contained in the first braking member and the first hydraulic chamber of the master cylinder, characterized in that the booster comprises, in front of the first partition: - a second partition, movable inside the rigid envelope, delimiting in a sealed manner a second front chamber, communicating with the first front chamber, and a second rear chamber, communicating with the first rear chamber, the second rear chamber being separated from the first front chamber by a rigid partition, - a second tubular movable pneumatic piston which is mounted slideably in the envelope, which is traversed coaxially by the return spring of the first pneumatic piston and by the rod for actuating the first hydraulic piston, and of which a front portion is secured to the second movable partition, the said second pneumatic piston being coupled to a second hydraulic piston sliding in a second hydraulic chamber of a second master cylinder connected to at least a second braking member of the vehicle, in order to make it possible to actuate the said second hydraulic piston without the reaction force of the hydraulic fluid contained in the second braking member and the second hydraulic chamber of the second master cylinder being transmitted to the control rod. - a second partition, movable inside the rigid envelope, delimiting in a sealed manner a second front chamber, communicating with the first front chamber, and a second rear chamber, communicating with the first rear chamber, the second rear chamber being separated from the first front chamber by a rigid partition, - a second tubular movable pneumatic piston which is mounted slideably in the envelope, which is traversed coaxially by the return spring of the first pneumatic piston and by the rod for actuating the first hydraulic piston, and of which a front portion is secured to the second movable partition,