Brakes: Braking Systems

Braking fundamentals	Principles of braking	Friction between braking surfaces converts kinetic energy into heat. In drum brakes, wheel cylinders force brake linings against the inside of the drum. In disc brakes, pads are forced against a brake disc.
	Drum & disc brakes	Drum brakes have a brake shoe that expands against the inside of a drum; disc brakes clamp a flat disc between two pads; an antilock braking system is a control system that applies maximum braking force without wheel-lock or skidding.
	Coefficient of friction	The coefficient of friction is the measurement of friction between pairs of surfaces.
	Lever/mechanical advantage	Mechanical advantage (MA) is the factor by which a machine multiplies the force put into it.
	Hydraulic pressure & force	Hydraulic pressure is transmitted through liquid & can transmit increased force.
	Brake fade	Fade, or brake fade is the reduction in stopping power caused by a buildup of heat in the braking surfaces (and in the case of drum brakes the change in dimension of components in response to heat).
	Regenerative braking	Regenerative braking is any technology that allows a vehicle to recapture and store part of the kinetic energy that would ordinarily be lost when braking.

Braking systems	Brake type – principles	Drum brakes have a drum attached to the wheel hub, with disc brakes a disc attached to the wheel hub maybe clamped between 2 brake pads, and ABS prevents the wheels from locking while braking.
	Brake types	Drum brakes have a brake shoe that expands against the inside of a drum; disc brakes clamp a flat disc between two pads; an antilock braking system is a control system that applies maximum braking force without wheel-lock or skidding.
	Air brakes	Air brakes are used on heavy vehicles and use compressed air to provide the large braking forces required.
	Exhaust brakes	An exhaust brake works by restricting the flow of exhaust gases through the engine, which slows engine rotation.
	Electric brakes	Electric brakes are commonly used with trailers and are activated when the brakes in the towing vehicle are applied.
	Parking brakes	All vehicles must have two independent braking systems. On some vehicles the park brake can also be applied manually in an emergency.
	Engine brakes	Engine braking is the act of using the energy-requiring compression stroke of the internal combustion engine to dissipate energy and slow down a vehicle.

Braking system components	Park brake system	The primary components of the park brake system are: Parking brake cables; Disc brake caliper fitted with park brake; Park brake lever on drum brakes.
	Brake pedal	The brake pedal acts as a lever to increase the force applied to the brake pedal pad, by the driver.
	Brake lines	Brake lines carry brake fluid from the master cylinder to the brakes. For most of their length they are steel, and attached to the body with clips or brackets to prevent damage from vibration. They are much the same on all brake systems.
	Brake fluid	Brake fluid is a special purpose high-boiling point fluid. It transmits the hydraulic pressure generated by the master cylinder to the brake units.
	Bleeding	When you bleed an hydraulic system you are removing air from the system.
	Master cylinder	The single-piston master cylinder transforms the applied pedal force into a hydraulic pressure which is transmitted simultaneously to all 4 wheels.
	Divided systems	Braking ability depends on the load on a wheel during braking. Front-engined, rear-wheel cars use a braking system with a front-rear split, or with an L-split. Most front-engined, front-wheel-drive vehicles use a diagonal configuration.
	Tandem master cylinder	The tandem master cylinder transforms applied brake force into hydraulic pressure which is transferred to the wheel units through 2 separate circuits. This provides residual braking in the event of fluid loss.
	Power booster or brake unit	The power booster assists the driver by reducing the amount of effort that has to be applied to the brake pedal during braking.
	Hydraulic brake booster	The system utilizes hydraulic pressure generated by the power steering pump rather than engine vacuum to provide the power assistance required in a conventional system.
	Electrohydraulic braking (EHB)	Replaces the current modulator with one that includes a high pressure accumulator.
	Applying brakes	As the brakes are applied, the pedal pushrod transmits movement through the power unit to the master cylinder piston to apply the brakes.
	Brake force	The power booster uses pressure differences in a diaphragm unit to increase the force being applied in the brake circuit.
	Brake light switch	We must be able to indicate to the people driving behind our vehicle that we are slowing down or stopping.

Drum brakes & components	Drum brake system	Drum brakes are still found on older vehicles, and on cars with a combination of both disc and drum brakes.
	Drum brake operation	The drum brake system operates by forcing the friction-lined brake shoes against the inner surfaces of the rotating drums. The shoes are designed to operate with a self-energizing action.
	Brake linings & shoes	The brake lining is a specialized friction material, riveted or bonded to a steel shoe. The shoe transfers the wheel cylinder movement and forces the lining against the rotating drum.
	Backing plate	The backing plate is bolted to the axle housing or suspension member. It provides a mounting for the wheel cylinders and brake shoes to act against the rotating drum.
	Wheel cylinders	The wheel cylinder and piston react to hydraulic pressure from the master cylinder, and the outward movement of the piston forces the shoe and lining against the drum.

Disc brakes & components	Disc brake system	Modern passenger vehicles are usually equipped with disc brakes on at least two wheels.
	Disc brake operation	The disc brake system converts the hydraulic pressure generated at the master cylinder into a frictional clamping force against the rotating discs.
	Disc brake rotors	The brake disc rotates with the road wheel. It provides a smooth surface against which to force the brake pads, to slow or stop the vehicle.
	Disc brake pads	A disc brake pad has a rigid, molded, friction material bonded to a steel backing plate for support during brake application. It transforms the hydraulic force of the caliper into a frictional force against the disc.
	Disc brake calipers	Disc brake calipers provide a housing for the hydraulic piston or pistons that force the brake pads into contact with the disc.
	Proportioning valves	The proportioning valve divides up the braking effort applied to front and rear wheels under heavy braking, according to how load is distributed across a vehicle.
	Proportioning valve operation	The proportioning valve adjusts the braking force applied to the wheels to allow for changes in load.

Antilock braking system & components	ABS brake system	The antilock braking system is designed to prevent wheels locking or skidding, no matter how hard brakes are applied, or how slippery the road surface.
	Antilock braking system operation	The antilock braking system prevents wheels locking or skidding, no matter how hard brakes are applied, or how slippery the road surface. Steering stays under control and stopping distances are generally reduced.
	Principles of ABS braking	The anti-lock braking system controls braking force by controlling the hydraulic pressure of the braking system, so that the wheels do not lock during braking.
	ABS master cylinder	The tandem master cylinder transforms applied brake force into hydraulic pressure which is transferred to the wheel units through 2 separate circuits. This provides residual braking in the event of fluid loss.
	Hydraulic control unit	The hydraulic control unit, or modulator, executes commands in the form of electrical signals from the ABS Control Module. It uses solenoid valves to change the hydraulic pressure in the brake circuit.
	Wheel speed sensors	Wheel speed sensors consist of a toothed rotor and a pickup. Wheel rotation sends input signals to the ECU, which processes them and controls the hydraulic control unit.
	ABS electronic control unit	The ECU receives signals from various sources. The brake pedal, the ignition system, and wheel speed sensors control the hydraulic control unit and anticipate wheel lock.

Brakes procedures	Checking & adjusting brake fluid	Brake fluid has a hygroscopic nature; it will absorb moisture rapidly. Always replace the cover or lid as soon as possible.
	Replacing brake fluid	Most manufacturers recommend that brake fluid be changed at least every two years.
	Checking brake pads	After checking the brake pads, replace the road wheel but don't put lug nuts into the socket of the impact wrench and power the lug nuts on.
	Replacing brake pads	Before you raise the vehicle, you will need to remove some of the brake fluid from the master cylinder.
	Removing & replacing a rotor	Clean the mating surfaces of the hub and rotor before assembly.
	Checking wheel cylinders	Check under the dust cap to make sure that the wheel cylinder is not leaking.
	Replacing brake linings	Never use any petroleum or mineral based products, such as gasoline, kerosene etc, to clean a braking system or its components.
	Adjusting a park brake cable	The park brake must operate independently of the service brakes.