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Module 2 - Hydraulic System Components (Page 1 of 5)

Hydraulic System Components

Master cylinder - the master cylinder pressurizes the brake fluid when the driver depresses the brake pedal.

Control valve - The control valve(s) is/are located between the master cylinder and calipers or wheel cylinders. Its purpose is to modify the pressures created by the master cylinder.

Front brake calipers require more pressure than rear wheel cylinders for two reasons. First, front calipers are not self energizing - they do not apply themselves. More on self-energizing brakes in module 1 . Secondly, since the vehicle weight shifts forward when braking in a forward direction, the front brakes are expected to do more braking than the rear wheels.

A combination valve such as the one pictured below often performs 2 or 3 tasks at once. More details later in this module.

Brake lines - Brake lines route the fluid to the wheel cylinders and calipers. Because brake lines are expected to handle thousands of PSI (pounds per square inch) of brake fluid pressure, brake lines are always made of double walled steel. No other steel lines are suitable for the brake system (ie: single wall steel or copper are unsuitable for brake lines).

Wheel cylinders - Used with drum brakes. Pressurized brake fluid enters the wheel cylinder and forces the two pistons outward to actuate the brake shoes. The spring (#5 in the diagram below) is to ensure the expander (#4) contacts the piston cup (#3). Otherwise, the piston cup may collaspe causing a brake fluid leak. The spring (#5) does NOT retract the pistons (#2).

Calipers - Used in the front or rear brakes. Unlike wheel cylinders and brake drums, front calipers and brake rotors are fully exposed to the ambient air. Therefore they have the ability to quickly dissipate the heat generated by braking.

Module 2 (Page 1 of 5)