Michigan State Brakes Certification Practice Exam 2025 - Free Brakes Certification Practice Questions and Study Guide

When vacuum is present on both sides of the diaphragm in a brake booster, it indicates that an equal force is acting on either side, which results in the diaphragm staying in a neutral position. This means that the power assist provided by the brake booster is not engaged, leading to the brakes being released. The brake booster operates by creating a differential pressure; when the brake pedal is pressed, it allows atmospheric pressure to act on one side of the diaphragm while maintaining vacuum on the other side. This imbalance in pressure helps to increase the force applied to the brakes. If both sides have vacuum, that pressure difference does not occur, meaning the brakes will not engage.

This condition does not indicate a malfunction, a low brake pedal, or that the brakes are applied, but rather that the system is in a state where the brakes are in the released position.