What causes brake fluid to return to the master cylinder reservoir after drum brakes have been applied and released?

When drum brakes are applied, the brake shoes press against the inside of the drum, creating friction to slow or stop the vehicle. Upon release of the brake pedal, the brake shoe return springs play a crucial role in retracting the brake shoes back to their resting position. As the shoes return to their original position, they pull back on the wheel cylinder, which creates a negative pressure in the hydraulic system. This negative pressure allows brake fluid to flow back from the brake line into the master cylinder reservoir, ensuring that the braking system maintains the proper fluid level and pressure for future braking actions.

Understanding the function of the brake shoe return springs is vital, as they are integral to the overall performance and effectiveness of the drum brake system. Their ability to retract the shoes promptly helps in reducing brake drag, which can lead to better fuel efficiency and prolonged brake component life.