Tech Tips - Understanding and maintaining your vehicle's braking system

The purpose of your braking system is to provide a method for slowing and stopping your vehicle in a controllable manner. When you push on the brake pedal inside your car, a hydraulic piston pushes brake fluid from the master cylinder through the brake lines forcing the brake pads against a disk or drum where friction inhibits the turning of the car's wheels. The pressue of the hydraulic fluid may be modified by a brake booster system that makes it easier to apply more force to the braking system or by an antilock brake system that pulses the pressure to wheels that are "locked up" allowing more control to the driver during hard, panic type stops. Modern vechicle stability control systems (aka The Nanny) may use complex feedback loops through the main vehicle computer, or brain, to provide precise adjustments to the braking system to aid in cornering or avoidance maneuvers.

Keeping your braking system properly maintained is vital to your vehicle's performance and stopping efficiency. A poorly maintained braking system will eventually cause wear on expensive components and may lead to a dangerous condition in which the vechicle fails to stop or skids uncontrollably in a panic braking scenario.

Master Cylinder: The role of the master cylinder is dual fold: storing excess brake fluid until it's needed and to convert the pushing force from the brake pedal into a hydraulic force that can transfer through the brake lines. Master cylinders are built to last a long time, but can still wear out. A leaking master cylinder is a dangerous condition and should be repaired or replaced right away.

Vacuum Booster: The vacuum booster sits directly in front of the master cylinder and uses vacuum from the engine to increase the force applied by the driver to the brake pedal so the pedal is easier to push.

Brake Lines: There are two types of brake lines. Solid metal lines run throughout the vehicle's chassis and connect the master cylinder to the ABS module eventually terminating near each wheel. At the wheel well, the solid metal lines connect to flexible rubber hoses which move as the wheels turn right to left of move up and down with the vehicle's suspension system. Brake lines should be inspected regularly for wear or damage.

ABS Module and Sensors: These devices provide a feedback loop between the wheels of the car and the hydraulic pressure applied to the brake pads controlling that wheel. The sensor is an electrical device that monitors the turning of the wheel. If the sensor detects the wheel has stopped turning or is turning more slowly than the other wheels, the anti lock braking (ABS) module will intermittantly interrupt hydraulic pressure to the brake line going to that wheel to allow it to turn. This action allows the wheel to contribute to the cars turning ability while also undergoing maximum stopping forces. This can, for example, allow your car to turn to avoid an accident while still slowing down from operating speeds.

Wheel Cylinders: When the hydraulic fluid from the brake lines enters the wheel cylinder, the cylinder expands in a controllable and leveraged manner to allow high forces to be applied to the brake pads. Most front wheel cylinders are non-adjustable. The rear wheels on most trucks use a shoe and drum combination that has a star adjuster. The rear shoes should be adjusted so the pads lightly drag on the drum when the brake pedal is not being pushed.

Brake Fluid: Brake fluid is a specialized hydraulic fluid optimized for use in your braking system. These fluids are DOT graded to produce predictable performance in your vechicle's braking system. Brake fluid is a "wear item" that must be replaced regularly for predictable performance. This is because brake fluid is hygroscopic meaning it attracts moisture from the air. Brake fluid is also susceptible to contamination from friction wear components (mostly from rubber seals and tiny metallic dust) which enter the fluid as the pistons move during brake application. Your vehicle's owner's manual will most likely identify a brake fluid replacement and flushing interval and this should be observed for best braking performance.

Brake Pads: The brake pads are the friction material that actual does the stopping of the car's wheels. The brake pad is forced against a metallic disk (rotor) or drum by the hydraulic pressure acting on the wheel cylinders. The brake pads are a wear item that must be replaced. Almost all modern brake pad systems employ the use of an indicator, or squeeler, that alerts the owner when the brake pads are getting close to wearing out. This indicator is a thin piece of metal which extends just beyond the edge of the brake pads wear surface and contacts the brake disk just as the pad material is about to wear away. Do not ignore this sound! It is your car telling you it is time for new brake pads. Replacing the brake pad in time will prevent damage to expensive rotors or drums. There are a wide variety of aftermarket brake pads available which can change the way your vehicle stops. More agressive (biting) pads may be appropriate for high performance driving or for towing heavy loads. Some agressive pads may handle braking heat better but may also release more brake dust which can darken the rims of your car's wheels. Stock pads will perform the same way as the car did when it was new.