Ideal Engines - Explanation of a Modern Brake System

This will be an attempt to familiarise you with a typical modern day brake system found on many passenger cars. The brake system I will be referring to has ABS brakes and is comprised of the following major components; the brake pedal, the vacuum brake booster, the master cylinder, a proportioning valve, front and rear brake hoses, front brake callipers, rear brake callipers or wheel cylinders depending on if the vehicle has rear drum or disc setup, brake discs, brake pads, and brake shoes. Those are the mechanical side of the brake system, the ABS portion of the brakes comprises of the ABS pump, the modulator valve, and the vehicle speed sensors.
Now, going down the line as they work they can be described a bit more fully. As you depress the brake pedal it is connected to a lever under your dash which goes through the vacuum booster and then into the master cylinder.Without the assistance of the vacuum booster the brake pedal becomes very hard and unresponsive, with the vacuum booster working properly the pedal depresses and pushes the plunger in the master cylinder to force brake fluid to build pressure in the brake lines.
As pressure is built up in the lines it travels through the proportioning valve which routes the right amount of fluid pressure to both the front and rear brakes. Without that valve the vehicle would not stop properly as because many vehicles are much heavier at the front than the rear, if they had the same pressure both front and back, the rear brakes would lock up and cause the back of the car to slide out because of loss of traction.
After passing through the proportioning valve the fluid is router to (front wheels- through the brake hoses and into the callipers)(rear wheels- through the brake hoses and into either wheel cylinders (drum brakes) or brake callipers) as the fluid compresses in the front brake callipers they cause the pistons to compress on the brake discs causing friction that in turn stops the vehicle. As the fluid goes to the rear it passes through brake hoses into either wheel cylinders or brake callipers, if it is a read drum system the brake fluid pushes out on the pistons in the wheel cylinders pushing the brake shoes against the inside of the brake drums creating friction to allow the vehicle to stop. If it is a rear disc brake set up them it works the same as with front discs.
The ABS or antilock brake system is an independent system from your normal service brakes, it is plumbed into the regular system and fluid does pass through it but it has its own design function all triggered by the vehicles speed sensors. If a speed sensor notices a tyre has come to a stop while others are still rotating it will stop adding pressure to the wheel that has stopped and actually release the pressure until that wheel begin to turn at the same speed as the other wheels on the vehicle. It then cycles itself in order to add fluid incrementally to all of the wheels to allow a controlled stop.
That is the most basic description of a current brake system that I can give without breaking down each part and making this a four thousand word essay, I think I will leave that for a later day.


  rental car