Which component transfers force from the diaphragm to the master cylinder?

The component that transfers force from the diaphragm to the master cylinder is the Power Piston. In the context of brake systems, the Power Piston is part of a power brake booster system. When the brake pedal is pressed, the diaphragm within the booster flexes, creating a vacuum that effectively amplifies the force exerted by the driver's foot. This force is then transferred to the Power Piston, which moves and subsequently pushes against the master cylinder. This action is crucial as it helps to generate the hydraulic pressure needed to engage the brakes effectively.

In contrast, while the Power Booster and Vacuum Assist Booster both play roles in enhancing braking performance by creating the necessary vacuum to aid in brake application, they do not directly transfer the force to the master cylinder. The Return Spring, on the other hand, serves to return the pedal or piston to its initial position but does not participate in the force transmission process. This distinction underscores the importance of the Power Piston in converting the diaphragm’s movement into hydraulic pressure for braking action.