What component directly connects the driver's input to the hydraulic system?

The lever is integral to the brake system as it serves as the mechanism that transmits the driver's physical input through the brake pedal to the hydraulic system. When a driver depresses the brake pedal, the lever pivots and generates a force that activates the hydraulic system. This action results in the application of brake pressure, ultimately helping to slow down or stop the vehicle.

In contrast, while the power booster, return spring, and vacuum assist booster play important roles in enhancing braking performance or ensuring the system returns to its original state, they do not directly connect the driver's input to the hydraulic system. The power booster amplifies the force applied by the driver, the return spring ensures that the brake pedal returns to its resting position after being released, and the vacuum assist booster aids in making the pedal easier to press. However, it is the lever that directly relays the driver's action to engage the braking process.