brake system is the self-adjusting screw. The adjusting screw is basically a threaded device that extends and contracts. The head of the adjustment screw is a notched wheel with a cylindrical pin. The pin is capped with a washer and a slotted cap on each end. The slots fit into the brake shoes to add pressure as needed due to friction pad wear.
Much like the power-assist brakes, self-adjusting brakes existed almost as early as drum brakes but not as frequently through the decades. First appearing on the 1925 Cole, the Indianapolis-based company specialized in luxury cars, but the 1925 model would be its last. Self-adjusting brakes would not return until after the war when Studebaker adapted a Wagner Electric unit to its cars. Slow to catch on, the self-adjusting drum brakes continued to be fitted to more vehicles in the 1960s.
Antilock Brakes
Antilock brake systems (ABS) may sound more like a modern invention, but nothing could be further from the truth. French aviation pioneer Gabriel Voisin, the creator of Europe’s first engine-powered airplane and major manufacturer of military aircraft, developed the first antilock brakes.
Voisin became a manufacturer of luxury cars later in his career with a company he called Avions Voisin. Voisin first used the antilock brakes on aircraft in 1929. They were introduced in his automobiles shortly thereafter.
Mercedes-Benz debuted an electronic ABS in 1936, and the British Jensen sports cars used a similar basic electronic ABS in 1966. Other car manufacturers experimented with antilock systems with varied success until Ford hit upon the Sure-Track system in 1969 for the Thunderbird and Lincoln Mark III models. These systems were a Kelsey-Hayes antilock unit that included wheel sensors on each wheel that transmitted reference signals to a computer in the dash panel. There were some problems with the system, and it only controlled the rear wheels, but the theory was in place.
Chrysler and General Motors both offered ABS in 1971 as options. Ford joined the club in 1975 as options on its Lincoln Continental Mark II and the LTD Station Wagon. Antilock brakes became commonplace in the late 1990s, and even work trucks were fitted with these handy safety devices. Modern vehicles use ABS integrated with long- and short-range radar that can bring a car to a stop even if the driver doesn’t activate the brake pedal.
Theory of Braking Systems
Until the turn of the century, brake systems have not received the accolades that many of the other systems in automotive manufacturing have. Engines, transmissions, rear ends, wheels and tires, along with electrical and ignition systems have all earned their place in the limelight over the past century. Brakes, on the other hand, seem to have been more of a marketing item to the public than the actual applied science that the system is.
The theory of braking systems, most definitely a hard science, is not that complicated once some scientific terms are defined in common language.
Pascal’s Law and Hydraulic Operation
Pascal’s law, or Pascal’s principle, was first stated by French scientist Blaise Pascal about fluid mechanics and is a fundamental law in physics. In the simplest terms, Pascal’s principle describes that any pressure applied to a fluid inside a closed system will transmit that pressure equally in all directions throughout the fluid. This is the very reason that hydraulic power works in everything from heavy equipment and lifts to automotive braking systems.
Brake systems operate by the pressure on one pedal applying pressure to all wheel cylinders. This is Pascal’s law, which states that pressure applied to a fluid inside a closed system will transmit that pressure equally in all directions throughout the fluid.
The radial openings in most aftermarket rotors are channels or vents that go from the center of the rotor to the outside edge. These vents are often curved to draw hot air from the center of the rotor and route it to the outside, keeping the entire assembly cooler. Heat is the byproduct of the energy conversion created by braking.
The brake master cylinder is filled with brake fluid. The master cylinder is equipped with a piston that actuates when the brake pedal is pressed. This forces fluid through the brake lines to the wheel cylinders or calipers equally. The small force applied at the brake pedal produces a larger force when all four wheels are involved.
Energy Conversion
To get a vehicle in motion, an internal combustion engine converts chemical energy (combustion) into motion energy. In physics, this energy of motion is called kinetic energy. A car in motion has a lot of kinetic energy and it takes a lot of chemical energy to get up to its velocity. Having gained that kinetic energy during acceleration, it will maintain that energy unless the speed changes.
It is important to remember that the amount of work done to create this kinetic energy is the same amount of work needed to decelerate from speed to a state of rest. Physics also tells us that the total energy of an object remains constant; energy cannot be created or destroyed but only transformed from one form to another. This is also known as the law of conservation of energy. The braking system uses friction to convert the kinetic energy into thermal energy.
There are many factors that combine to make this energy conversion happen, including the brake pedal ratio and brake line diameter. Without getting into too many details, here is a basic overview of how most brake systems work:
The vehicle operator steps on the brake pedal to slow down or stop. The brake pedal lever is connected to a rod that pushes a piston in the brake master cylinder. The master cylinder is filled with hydraulic fluid that gets pushed into the brake lines by the piston. The hydraulic fluid presses against pistons in slave cylinders located on each wheel. The slave cylinders actuate either brake shoes or caliper pads against the brake drum or brake rotor, applying enough force to stop the vehicle.
Here’s where physics comes in. As the brake shoes or pads do their job, the kinetic energy of the vehicle is changed into heat. The biggest enemy to brake pads and brake shoes is heat. As the brake shoes or pads change the car’s motion energy into heat, the brakes get hotter. If they get too hot, they won’t work as well and will experience brake fade. It they get hot enough, the brakes will lose their ability to stop the car because the shoes or pads lose their friction against the drum or rotor. The amount of heat generated by the brakes stopping a car at speed can hit 950°F or more.
To combat brake fade, manufacturers use different materials with higher heat resistance for different applications. These materials that resist degradation at high temperatures include composites, alloys, and even modern ceramics. Some of these materials, especially those used in the higher-performance brake sets, have brake rotors and pads that require some heat in them to have enough friction in the first place. When they are cool, the brakes don’t have enough friction and won’t stop the car as well. These types of brakes are used mostly in race cars and not on cars driven on the street. Using brakes kits with different materials in the rotors, pads, shoes, or drums is one way to improve braking in muscle cars.
The brake pads ride very close to the rotor when they are not in actual contact. This leaves precious little room for cooling. Brake pad materials rely on mostly heat-resistant synthetic fibers to resist heating and brake fade. Ceramics and metal fibers from copper and other soft metals are also used in modern brake pads.
Most cars manufactured during the muscle car era were equipped with drum
