A brake control unit includes a primary piston and a secondary piston that respectively define a primary chamber and a secondary chamber. The primary piston carries an intermediate piston that slides in the secondary piston. A primary insulating seal is disposed between the pistons such that the primary insulating section of the primary insulating seal only depends on the equivalent section connecting the force applied at the inlet and the secondary pressure. The ratio of the hydraulic sections is configured to be modified without having to intervene on the primary and secondary pressure seals for the main piston and the secondary seal by way of modifying the section of the plunger piston and that of the seal thereof.