Michigan State Brakes Certification Exam Prep 2025

A brake pedal that slowly sinks to the floor under normal pressure typically indicates a problem with the hydraulic system, specifically suggesting that there may be a leak in the master cylinder primary piston seal. When this seal is compromised, it cannot maintain the hydraulic pressure required to keep the brake pedal in a raised position. As a result, when pressure is applied, the fluid can bypass the seal, causing the pedal to sink gradually toward the floor.

This scenario is distinct from issues such as a faulty brake booster, which primarily affects the assist and feel of the pedal rather than causing it to sink gradually, or air trapped in the brake lines, which would result in a spongy feel rather than a consistent downward movement. Worn brake pads can impact braking effectiveness but are not directly responsible for the pedal sinking. Thus, observing the symptom of a sinking brake pedal points clearly to the likelihood of a leaking master cylinder primary piston seal.