CDX/(ASE) “Brakes” “Hydraulics and Power Brakes”

Aerate

The tendency to create air bubbles in a fluid

Bleeding

The process of removing air from a hydraulic braking system.

Brake Fluid

Hydraulic fluid that transfers forces under pressure through the hydraulic lines to the wheel braking units.

Brake Hose

A flexible section of the brake lines between the body and suspension to allow for steering and suspension movement.

Brake Lines

Made of seamless, double-walled steel, and able to transmit over 1000psi of hydraulic pressure through the hydraulic brake system.

CAN-bus Circuit

A two-wire communication network that transmits status and command signals between control modules in a vehicle.

Compensating Port

Connects the brake fluid reservoir to the master cylinder bore when the piston is fully retracted, allowing for expansion and contraction of the brake fluid.

Electro-hydrualic Braking (EHB)

A hydraulic braking system that uses an electrically driven hydraulic pump to pressurize fluid for use in the master cylinder.

Free Play

The amount of clearance between the brake pedal linkage and the master cylinder piston.

Hygroscopic

A substance that attracts and absorbs water (e.g., brake fluid)

Inlet Port

Connects the reservoir with the space around the piston and between the piston cups in a brake master cylinder.

Input Force

The force applied to the input piston, measured in either pounds or kilograms.

International Standards Organization (ISO) Flare

A method for joining brake lines, also called a bubble flare. Created by flaring the lines slightly out and then back in, leaving the line bubbled near the end.

Inverted Double Flare

A method for joining brake lines that forms a secure, leak proof connection.

Load Transfer

Weight transfer from one set of wheels during braking, acceleration, or cornering.

Manual Bleeding

A bleeding method where one person manually operates the brake pedal while the other person opens and closes the bleeder screws on the wheel brake units to allow the air and old brake fluid to be pushed out.

Metering Valve

A valve used on vehicles equipped with older rear drum/front disc brakes to delay application of the front disc brakes until the rear drum brakes are applied. Located in line with the front disc brakes.

Output Force

Force that equals the working pressure multiplied by the surface area of the output piston, expressed as pounds, newtons, or kilograms.

Outlet Port

Links the cylinder to the brake lines.

Pascal’s Law

The law of physics that states that pressure applied to a fluid in one part of a closed system will be transmitted equally to all other areas of the system.

Poppet Valve

A valve that controls the flow of brake fluid at usually present pressures.

Pressure Bleeding

A bleeding method that uses clean brake fluid under pressure from an auxiliary tool or piece of equipment to force the air and old brake fluid from the hydraulic braking system.

Pressure Differential Valve

A valve that monitors any pressure difference between the two separate hydraulic brake circuits; it usually contains a switch to turn on the brake warning light when there is a pressure difference.

Primary Cup

A seal that holds pressure in the master cylinder when force is applied to the piston.

Primary Piston

A brake piston in the master cylinder moved directly by the pushrod or the power-booster; it generates hydraulic pressure to move the secondary piston.

Proportioning Valves

Valves used mostly on older vehicles equipped with rear drum brakes to reduce rear wheel hydraulic brake pressure under hard braking or light loads. Located in line with the rear brakes.

Quick Take-Up Master Cylinders

Cylinders used on disc brake systems that are equipped with low-drag brake calipers to quickly move the brake pads into contact with the brake rotors.

Quick Take-Up Valve

A valve used to release excess pressure from the larger piston in a quick take-up master cylinder once the brake pads have contacted the brake rotors.

Recuperation

Process by which brake fluid moves from the reservoir past the edges of the seal into the chamber in front of the piston. This prevents air from being drawn into the hydraulic system caused by low pressure when the brake pedal is released quickly.

Residual Pressure Valve (Residual check valve)

In drum brake systems, a value that maintains pressure in the wheel cylinder slightly above atmospheric pressure so that air does not enter the system through the seals in the wheel cylinder.

Secondary Cup

A seal that prevents loss of fluid from the rear of each piston in the master cylinder.

Secondary Piston

A piston that is moved by hydraulic pressure generated by the primary piston in the master cylinder.

Single-Piston Master Cylinder

A master cylinder with a single piston that creates hydraulic pressure for all wheel units. If there is a leak in the system, there is a loss of pressure for all wheel units.

Split Diagonally

A brake system in which the left front wheel is hydraulically paired with the right rear wheel and the right front wheel is paired with the left rear. This preserves 50% of the braking capability if one of the brake circuits begin to leak.

Split Front To Rear

A brake system in which the front brakes operate on one hydraulic circuit and the rear brakes from the other.

Tandem Master Cylinder

A master cylinder that has two pistons that operate separate braking circuits so that if a leak develops in one circuit, the other circuit can still operate.

Vacuum Bleeding

Bleeding process that uses a vacuum bleeder to pull the air and old brake fluid from the system.

Working Pressure

The pressure within a hydraulic system while the system is being operated.