When you get behind the wheel of your car to go to work or run an errand, you probably don’t think twice about whether or not your brakes are going to work. You trust that when you put your foot on the brake pedal that the car will stop. Perhaps surprisingly, the small amount of pressure you apply to the brakes can stop a two-ton vehicle. That is the magic of the hydraulic braking system.
The first cars built in the early 1900s were not equipped with hydraulic brakes. They had not been invented yet. Instead, they used mechanical brakes. These brakes physically transferred the brake lever’s mechanical pressure to the wooden blocks mounted next to the wheel.
When the driver pulled the brake lever, the blocks moved to be in contact with the metal-rimmed wheels. The friction created stopped the car. While this method worked for slow-moving vehicles, it did not work well for vehicles with rubber tires. The woodblocks destroyed the rubber. It was clear that a new braking system was needed.
In 1902, the mechanical drum brake was invented. Louis Renault of France is credited with this engineering feat. Renault designed a system in which pulling the brake lever would allow the brake shoes within the wheel to expand and push against the inside surface of the wheel. The friction would slow and stop the vehicle. These mechanical brakes became the standard brakes used in cars until the 1920s when hydraulic brakes appeared on the scene.
Mechanical brakes worked well for early generations of cars. These vehicles traveled relatively slowly, and the friction brake system could stop them quickly. However, depending on friction proved to be a problem in and of itself. By its very nature, friction creates heat causing wear and tear on the braking surface. As cars began to drive faster, they had to allow more stopping distance. Because this system contained multiple moving parts, it was also prone to failure and needed routine maintenance to keep it working correctly.
In 1918, Malcolm Loughead (aka Lockheed) proposed a new brake design with fewer moving parts that would stop cars faster and more reliably. The keys to his new system were the master cylinder and hydraulic fluid. In this new hydraulic braking system, the brake pedal or lever’s pressure is converted into fluid pressure by the master cylinder. The resulting pressure travels through the brake lines and triggers the brakes to slow or stop the car.
The introduction of hydraulic brakes brought many benefits to the car industry. Hydraulic brakes were capable of producing more pressure and stopping moving cars faster. With fewer moving parts, these systems require less maintenance and experience less wear. Any maintenance needed is easier to perform because it is not as complicated as mechanical brakes once were, and parts are easy to find. The hydraulic system is a closed system, meaning that nothing comes in or goes out if all is working as it should. That is why dripping brake fluid is always a red flag.
Types and Uses
Regardless of the braking system, the stopping mechanism is one of two main types.
• Drum Brakes – Also known as expanding brakes, these brakes are fitted with brake shoes inside a drum. As the brakes are applied, the shoes are forced outward into contact with the drum, which stops the vehicle.
• Disc Brakes – Mounted on the outside, these brakes are also called external contracting brakes. These brakes slow a vehicle by pressing the brake pad against the rotor mounted behind the car’s wheel.
In a hydraulic brake system, the master cylinder controls where the stopping power is sent. Single-acting cylinders can only send braking power in one direction. In the case of a car, the braking power would be limited to only the front two or back two wheels. The result is less braking ability and extended stopping distances. It would be similar to only applying the brakes on one wheel of a bicycle. Instead, most cars have double acting master cylinders capable of sending the pressure in both directions. Thus, the brakes on all four tires are triggered simultaneously to stop the vehicle.
By 1930, most family cars had hydraulic brakes. For a time, drum brakes were installed in some vehicles as a back-up. However, modern vehicles operate with only hydraulic brakes. Over almost 100 years of use, this system has proven itself safe, effective, and reliable. However, no system is perfect. If you are in the Salt Lake City area, visit a local repair shop to have your brakes checked if your brake pedal feels soft, you have trouble stopping, or you see signs of brake fluid. A quick check-up could save you from an accident down the road.