When testing a hydraulic brake with power assist, when you turn the engine on the pedal should...?

When testing a hydraulic brake with power assist, it is expected that the brake pedal will drop slightly when the engine is turned on. This occurs because the power brake system is designed to enhance the force applied by the driver on the brake pedal. Upon start-up, the engine creates vacuum pressure that assists with braking, which can lead to a slight movement of the pedal downwards as the system engages.

This slight drop indicates that the power assist is functioning properly, allowing the driver to apply less pressure on the pedal for effective braking. A drop to the floor or halfway would suggest a malfunction, such as excessive wear in the brake system or other hydraulic issues. If the pedal stays where it is, it could indicate no vacuum assist is being applied, which would also signify a problem with the system. Therefore, the slight drop is a normal and expected reaction when the power-assisted hydraulic brake system is functioning effectively.