Hydraulic brakes A hydraulic brake system typically consists of the following:
The system is usually filled with a glycol-ether based brake fluid (other fluids may also be used). Hydraulic fluid must be non-compressible. Unlike air brakes, where a valve is opened and air flows into the lines and brake chambers until the pressure rises sufficiently, hydraulic systems rely on a single stroke of a piston to force fluid through the system. If any vapor is introduced into the system it will compress, and the pressure may not rise sufficiently to actuate the brakes.Hydraulic braking systems are sometimes subjected to high temperatures during operation, such as when descending steep grades. For this reason, hydraulic fluid must resist vaporization at high temperatures. Water vaporizes easily with heat and can corrode the metal parts of the system. Water which enters brake lines, even in small amounts, will react with most common brake fluids.It is almost impossible to completely seal any brake system from exposure to water, which means that regular changing out of brake fluid is necessary to ensure that the system is not becoming overfilled with the deposits caused by reactions with water. Light oils are sometimes used as hydraulic fluids specifically because they do not react with water: oil displaces water, protects plastic parts against corrosion, and can tolerate much higher temperatures before vaporizing, but has other drawbacks vs. traditional hydraulic fluids.'Brake fade' is a condition caused by overheating in which braking effectiveness reduces, and may be lost. It may occur for many reasons. The pads which engage the rotating part may become overheated and 'glaze over', becoming so smooth and hard that they cannot grip sufficiently to slow the vehicle. Also, vaporization of the hydraulic fluid under temperature extremes or thermal distortion may cause the linings to change their shape and engage less surface area of the rotating part. Thermal distortion may also cause permanent changes in the shape of the metal components, resulting in a reduction in braking capability that requires replacement of the affected parts. At Auto Repair Service our ASE Master Certified Technicians can help you identify the problem before you find yourself in a potentially dangerous situation.
- Brake pedal or lever
- A pushrod (also called an actuating rod)
- A master cylinder assembly containing a piston assembly (made up of either one or two pistons, a return spring, a series of gaskets/ O-rings and a fluid reservoir)
- Reinforced hydraulic lines
- Brake caliper assembly - which will consist of one or two hollow aluminum or chrome-plated steel pistons (called caliper pistons), a set of thermally conductive brake pads and a rotor (also called a brake disc) or drum attached to an axle.