It goes without saying, your car's brakes are by far the most important system. It is a simple and effective system that can have many problems-some of them caused by outside forces, others caused by general wear. Here I will explain how your car's braking system works and some associated problems.
Brake fluid is basically a light silicate oil. It is very durable and will not break down rubber components like a standard petroleum oil will. This is why we don't use regular oil in a car's braking system-it will break down rubber components and make them soft and expandable. The fluid is retained in a reservoir above the brake master cylinder. The master cylinder moves the fluid to the various different parts of the braking system and squeezes or pushes pistons to apply a friction material to a metal surface attached to the wheels of the car.
Let's get a more in-depth look...
When you apply your foot to the brake, you will exert a pressure equal to about 25 lbs in normal braking. How will 25lbs stop a three-ton car? Force multiplication from the vacuum booster and hydraulic advantage. Your 25lbs of force is transformed in to 250-300 lbs of force on the wheels of the car. Multiply 300lbs of force times four wheels and you have a whopping 1200lbs of braking force to stop your car. Basically, the vacuum booster takes vacuum power from your engine's intake manifold and applies it to the braking system. The pulling of the vacuum from the engine creates a partial vacuum on one side of a diaphragm inside the booster. This diaphragm is connected to a rod that pushes a piston in the master cylinder to move fluid to the different components. It will multiply your force by 10 times in some cases! The piston in the master cylinder is much smaller than the pistons in the wheels, so the smaller amount of force exerted by the master cylinder is multiplied by the hydraulic advantage. It's kind of like pumping a bottle jack-you pump the smaller piston 15 times to get the same amount of movement out of the main piston.
Once the piston in the master cylinder is pushed in, the fluid travels through pipes throughout the vehicle to a valve that controls how much pressure is distributed to each wheel. It proportions the brakes for the optimal control, hence the name proportioning valve. In a typical automotive braking system, 70% of braking force is applied to the front, while 30% is applied to the rear. In some systems, the proportioning valve has a lever attached to the rear axle and adjusts force dependent on the weight of passengers and cargo. This is a load-sensitive proportioning valve.
After the proportioning valve, the fluid travels to the flexible hoses. These hoses are a durable, reinforced rubber material that can withstand an excessive amount of movement and pressure. With the movement of the wheels in bumps and cornering, the hoses provide the fluid with a universal pathway to their destination, unlike with a steel pipe which must remain stationary or it will break.
In a disc braking system (which is most common on cars and trucks today), the brake fluid travels to the caliper. The caliper is an iron or aluminum bracket that incorporates a piston that will squeeze tight on it's intended target while remaining mounted solid. Brake pads are made of a steel plate with a friction material bonded or riveted to it. The friction material today is a ceramic compound with bits of steel for strength and heat resistance. The pads and their friction material contact a rotor, which is attached to the back of the wheel and spins with the motion of the car. The brake rotor is typically made of strong cast iron, so it will not break or crack under extreme temperatures.
Years ago, cars had drum brakes on the front. Now, drum brakes are typically reserved for the rear brakes of some cars, although a majority of cars on the road today have disc brakes on the rear as well. A drum braking system is a totally different animal from a disc system. Instead of pads, it uses shoes. They are not constantly self-adjusting like a disc system. In a drum system, the friction material is pushed out by the force of the fluid, rather than squeezed together. The wheel cylinder accepts the brake fluid from the master cylinder and will push the shoes outward to the inside of a drum. The drum fits over the whole works and keeps everything in place.
Typical problems with automotive braking systems are worn lining, fluid leaks, and warped friction surfaces.
The drums and rotors must be perfectly round and flat to provide smooth braking. When a rotor heats up unevenly from hard braking or component failure, it will become warped. I'm sure everyone has driven a vehicle in their life where the brake pedal shakes, the steering wheel shakes, and it sounds like the whole world is coming apart when the brakes are applied. This is the case for most brake pulsations and vibrations.
Worn linings are an inevitable way of life for any car owner. There is no way around it; your brakes will have to be replaced at some time or another. The friction material on the pads and shoes will wear off as braking is used. It's like using a pencil eraser-it won't last forever. Typically, the brake pads have a warning system in place that drags a bit of metal along the side of the rotor to indicate that the lining is worn. This will cause a squeaking sound that is enough to make a deaf dog howl. Change your pads at this point or expensive damage will result!
Fluid leaks happen with rusting and damage to components. The steel pipes in a braking system are exposed to the elements of the road and will corrode and rust just as the body of the car. The only difference is, the body of the car is protected with paint-steel pipes are not. Eventually a loss of brake fluid can yield a loss of brakes altogether in your vehicle. This can be prevented by simply inspecting your brakes and all of the components.
If you need some help inspecting or diagnosing your braking problems, we are here to help! Email us at diyfixyourcar@gmail.com and we will provide you with free help!
