Michigan State Brakes Certification Practice Exam 2025 – All-in-One Study Guide for Exam Success!

A plugged booster air breather would indeed cause an abnormal amount of pedal effort in a vacuum assist power brake system. The vacuum assist relies on atmospheric pressure to assist in the application of the brakes. When the air breather is blocked, it creates a pressure differential that prevents the booster from functioning correctly. This results in increased effort required to push the brake pedal and engage the brakes effectively.

The other potential causes could lead to brake issues, but they would not specifically explain the abnormal pedal effort associated with the vacuum assist mechanism. For instance, a defective brake pedal could lead to problems with the pedal's engagement action rather than the effort required. A faulty brake proportioning valve could cause uneven braking or a different brake feel, but not specifically an increase in pedal effort. An improperly adjusted brake pedal would more likely lead to issues in travel and engagement of the brakes rather than requiring additional effort to push the pedal. Hence, the plugged booster air breather is the most direct cause of the increased effort in the brake pedal.