Georgia Commercial Driver License Practice Test

What is the most common type of foundation brake used?

1. Disc brake

2. Drum brake

3. Air brake

4. S-cam drum brake

The correct answer is: S-cam drum brake

The most common type of foundation brake used in commercial vehicles is the S-cam drum brake. This type of brake system is prevalent because of its effective design and reliability, particularly in heavy-duty applications. The S-cam brake operates using a cam that, when actuated by air pressure, causes shoes to spread outward against the inside of a drum. This mechanism provides strong stopping power suitable for large vehicles that require reliable braking in various conditions. The S-cam design allows for effective use of mechanical leverage, translating air pressure effectively into lateral force, which enhances braking efficiency. This system is also relatively simple to maintain and repair, contributing to its widespread use in trucks and buses. While disc brakes are also used in some applications, particularly in newer models for their performance and heat dissipation qualities, they are not as ubiquitous as S-cam drum brakes in the commercial sector. Similarly, the term "air brake" encompasses a broader category that includes various brake designs that use air pressure, but when specifically considering foundation brakes, the S-cam drum brake is the most common.