Hendersonville Muffler can handle all of your engine repair and replacement needsRead More
Hendersonville Muffler can handle all of your engine repair and replacement needsRead More
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The technicians at Hendersonville Muffler repair many different systems on cars and trucks every day. Take for example brakes and the individual components that make up the braking system. Everyone wants their braking systems working correctly but most technicians only look at the brake pads and brake shoes when performing a safety check on the vehicle. The braking system is just that. A system of components that work together to stop the car or truck. I wrote this page to explain a little about each component of the automotive braking system as the whole system must work together to reliably stop your car or truck.
The original cars used cable operated braking systems. They used only mechanical force to actuate the brake shoes. If you got the car up to any speed at all you could not get the car, or even worse, a truck to lock the tires up and stop the vehicle quickly.
Then hydraulic brakes were invented. By using hydraulic pressure against the brake shoes you could apply thousands of pounds of pressure to the brake shoes while only applying a small amount of pressure with your foot. By it's name and definition hydraulic means liquid. The original hydraulic systems used water to operate. Believe it or not water does an excellent job in hydraulic systems. Many hydraulic systems in use today still use water to produce hydraulic pressure. The main problem with using water for braking systems was that the water would boil out of the brake reservoir too quickly. A second problem was that water caused corrosion in the system. Yet a third problem is that water does not offer very many lubricating properties. Automotive Engineers needed a fluid that would supply all of these needs so a fluid was invented that would serve all of these functions at once and it was named simply brake fluid.
Brake fluid has undergone a few changes over the years but the original principal requirements are still there. The fluid must withstand high temperatures without boiling out of the brake fluid reservoir. Brake fluid must keep the internal components of the braking system lubricated and allow the components to slide against one another without damaging each other. Brake fluid also has corrosion inhibitors which do a good job of keeping the internal components of the braking system from deteriorating from corrosion. Hydraulic fluid is used in many other applications but it's slippery oil based formula was dangerous in braking system applications. (Brake fluid is not petroluim based and mixes or rinses completely with water). When you consider all of the advantages that brake fluid brought to the auto industry it is amazing it does not cost more.
Brake fluid is and always has been stored in an area called the brake fluid reservoir. A reservoir is just a French word for a liquid bearing container. The original brake fluid reservoirs were just a hollow area in the top of the master cylinder. This worked pretty well and this method is still used by many manufacturers today. However most car and truck manufacturers today use a plastic see through brake fluid reservoir so that the owner of the car can check the brake fluid without getting dirty. This also allows technicians to see when the fluid becomes contaminated. (If you look into the brake fluid reservoir and the fluid is any color other than what it originally was then it is time to flush the system and replace the brake fluid) Most brake fluid is clear but a few synthetic fluids are red or purple. Any time you look at your brake fluid and it is black you need to have the brake fluid flushed out. Black fluid is normally contaminated with algae. Because brake fluid mixes with water moisture from the air mixes into the system and carries with it algae and the acids that algae produce. The brake fluid is probably the single most important part of the modern braking system.
When cars were first invented they were mostly driven by only men. You had to be strong to start them, strong to stop them, and strong to turn them. As cars and even trucks progressed more women started driving and also children started driving at an earlier age. Electric starters were added to cars. Soon after cars started using a hydraulic steering system which engineers named power steering. Soon after this engineers decided that they could shorten the brake pedal, (and the mechanical advantage the long lever offered) allowing shorter people to drive cars and trucks. The systems using this shorter brake pedal with less travel were named power brake systems.
Power brake systems use a device called a brake booster to help you push the master cylinder piston and actuate the brakes. There are several types of brake boosters used in cars and trucks but the most common is the rubber diaphragm power brake booster. When you apply your foot to the brake pedal the pedal moves the brake booster input rod and a valve in the brake booster opens up. Engine vacuum which has been stored in the brake booster pulls against a large diaphragm. As the diaphragm travels towards the master cylinder from this vacuum force a rod called the brake actuator rod pushes against the master cylinder piston. The master cylinder piston then forces the brake fluid through brake lines to the other components of the braking system with greater force than would be gained if you only used mechanical leverage.
When cars and trucks used carburetors stealing a small amount of vacuum from the engine didn't really cause any problems with performance. Problems with this system generally started when diesel engines became more popular. Diesel engines do not trap vacuum behind the throttle plate the way gasoline engines do. Most diesel engines that use vacuum power braking systems had to have an external vacuum pump. This extra pump that pumped fresh air and pulled it into a vacuum for the vacuum brake booster. There was no real way for the impeller to stay lubricated or cooled and so many of these pumps produced unwanted failures in the power brake system. Turbocharged and supercharged cars and trucks had the same issues with low vacuum during periods where the engine was receiving boost instead of drawing air into the engine with vacuum.
A new system was devised using the pressure form the power steering pump. The hydraulic brake booster system operates in a similar manner to the vacuum brake booster system. The driver hits the brake pedal. the brake booster input shaft again pushes a valve which in turn releases hydraulic fluid pressure against a piston in the hydraulic brake booster. When the piston of the hydraulic brake booster is forced forward from the hydraulic pressure the brake booster piston moves the brake master cylinder actuator rod against the brake master cylinder piston. The brake master cylinder then pushes the brake fluid to the rest of the braking system to stop the car or truck.
With all of this extra equipment designed to help you exert pressure on the master cylinder and other brake components like disc brakes that began to give greater braking force to the wheels automotive engineers started noticing problems with the rear brakes locking up too easily. The engineers designed several small valve assemblies which would send a regulated amount of fluid to the rear brakes before it sent any brake fluid to the front brakes called brake proportioning valves. Proportioning valves limit the amount of fluid that travelers to the rear brakes in systems with front disc brakes and rear drum brakes when a large amount of pressure was applied by the brake master cylinder very quickly, (indicating a panic stop).
As I said before brake proportioning valves were originally just made to operate on vehicles that had front disc brakes and rear drum brakes. Some later brake proportioning valves were designed so that they had a rod attached to the suspension arm. As the rear suspension begins to rise the pressure is reduced to the rear brakes. This keeps the rear brakes from locking up during hard braking. Even though cars and trucks are now equipped with anti-lock braking systems, the braking system behind the ABS system needs to be capable of stopping the vehicle well without the use of the ABS control unit and pump system, just in case the ABS system fails.
As cars have become more complex and anti-lock braking systems have become mandatory the brake proportioning valve has often been incorporated into the combination valve. In the newest vehicles the brake proportioning valve has been replaced by a newer version which is called the Electronic Brake Proportioning Valve or EBP. On braking systems that are equipped with EBP valves the ABS unit controls the EBP valve.
Technology never stops and modern cars are now equipped with Anti-Lock braking systems. Anti-lock braking systems can be explained in greater detail here but this page is designed to explain the components of the braking system and ABS systems have extra components to operate correctly. ABS systems use wheel speed sensors, brake pressure sensors, transmission speed sensors, and valve assemblies.
I hope that this page has helped you have a better understanding and appreciation of the components needed for a braking system to operate but the truth is if you don't understand how all of these components work you should not be repairing your own brakes. At Hendersonville Muffler we constantly study new technologies and we have a great understanding of how these brake components work. Remember that all of these components are part of the braking system. This is the most important system in any car or truck. Mistakes in the braking system may cause your car or truck NOT TO STOP when you want it to. Let the professional technicians at Hendersonville Muffler handle all of your brake system repairs. Stopping when you want is much better than the alternatives