A Little Bit To Know About Automotive Brake System... Rev A 11-09-08 The cars we know today have been refined tremendously over the years. From the early days steam-powered self-propelled vehicles to modern "hybrid cars", the cars have become more realiable and dependable so much so that most people have forgoten to appreciate the technology behinds their driving wheels - out of sight, out of mind The same thing happens to the brake system that our lives depend on every moment we are on thr road; many people's knowledge of brake system merely stay at the single brake pedal that they step on to slow down or to stop the cars completely. The information in this leaflet would try to shed some light or peek into what happen when brake pedal is being stepped on... Have you ever wondered how can our foot stop a roaring car weights more than 1 ton speeding at 110-km/hr (a law abiding Malaysian driver on PLUS highway!)? The trick would be in the Leverage (mechanical advantage) and Pascal's Law (hydraulic force multiplication) we learned in secondary school's physics class. The Pascal's Law states "a change in the pressure of an enclosed incompressible fluid is conveyed undiminished to every part of the fluid and to the surfaces of its container." Simply put, let's say by stepping the brake pedal down 3-cm applying 10-kg force, we might obtain in return, by transmitting the brake fluid through the cleverly designed brake fluid circuit via those brake hoses and lines, a whopping 1,000-kg force or more acting on the brake disc at the wheels! Of course, the catch is the brake piston can only extend a few millimeter…

Figure 1. Leverage and Pascal's Law on Brake System

Figure 2. Typical Non-ABS Brake System

A typical brake system consists of: Brake Pedal - uses leverage to transfer the multiplied effort from the driver's foot to the master cylinder. Master Cylinder - located under the hood connected directly to the brake pedal, acts as a holding tank for brake fluid until it is needed. When the brake pedal is depressed, the master cylinder forces fluid to each of the vehicle's wheels. Metal Brake Lines and Flexible Brake Hoses - connect the master cylinder to the wheel or slave cylinder located at each wheel. Brake Fluid - to transmit pressure and motion in the brake system. Due to the intense heat generated by components of the brake system, the brake fluid must have a high boiling point. The brake fluid must have low freezing (melting) point for proper operation at any low temperature operation that the vehicle may encounter. 2 types of brake fluids are available, namely glycol based (DOT-3 and 4) and silicone based (DOT-5); rated by Department of Transportation (DOT), USA based on their boiling points. Brake Booster - available in the power-assisted brake system that uses the engine's energy to add pressure to the master cylinder. Disc Brake - uses a clamping action to produce friction between the brake disc and the brake pads mounted in the caliper attached to the suspension members. When the brake pedal is pushed, brake fluid from the master cylinder compresses the brake pads against the brake discs. The friction between the stationary brake pads and the revolving brake disc causes the brake discs and wheel to slow and stop. Disc brake works using much the same basic principle as the brakes on a bicycle; as the caliper pinches the wheel with pads on both sides, it slows the bicycle. Drum Brake - brake drum is a heavy flat-topped cylinder, which is sandwiched between the wheel rim and the wheel hub. The inside surface of the drum is acted upon by the linings of the brake shoes. When the brake pedal is pushed, pressure from the master cylinder causes the wheel cylinder to push the brake shoes against the brake drums which are attached to the vehicle's wheels. The friction between the stationary shoes and the revolving drums causes the drums to slow and stop the wheels.

Figure 3. Disc Brake Assembly

Figure 3. Drum Brake Assembly

Brake system is actually an energy conversion device that converts kinetic energy (car in motion possessing momentum) to potential energy (car stopping) through dissipating heat and noise to the surrounding air. The friction surfaces of the brake pads on a disc brake, or the brake shoes on a drum brake convert the forward motion of the vehicle into heat. Heat is what causes the friction surfaces (linings) of the pads and shoes to eventually wear out and require replacement. When the time is up for brake pads or shoes replacement, the driver would notice audible squealing noise during braking. As mentioned earlier, brake system is often neglected by most driver; we should instead pay more attention to it as our safety on the road very much depends on the proper function of the system. As a minimum, the brake system should be inspected by a qualified mechanic once a year for the linings wear out, brake fluid leakage, brake disc thickness variation, broken seals and etc.