Close-up of a disc brake on a car

Brake bleeding is the procedure performed on hydraulic brake systems whereby the brake lines (the pipes and hoses containing the brake fluid) are purged of any air bubbles. This is necessary because, while the brake fluid is an incompressible liquid, air bubbles are compressible gas and their presence in the brake system greatly reduces the hydraulic pressure that can be developed within the system. Image File history File links Download high resolution version (2260x1896, 1727 KB) Disk brake Photo on a Renault hollowed-out car at the Salon Européen de la Recherche et de lInnovation, June 5 2005 Copyright © 2005 David Monniaux File links The following pages link to this file: Disc... Image File history File links Download high resolution version (2260x1896, 1727 KB) Disk brake Photo on a Renault hollowed-out car at the Salon Européen de la Recherche et de lInnovation, June 5 2005 Copyright © 2005 David Monniaux File links The following pages link to this file: Disc... Hydraulics is a branch of science and engineering concerned with the use of liquids to perform mechanical tasks. ... Brake fluid is a type of hydraulic fluid used in brake applications in automobiles and light trucks. ... Physical compression is the result of the subjection of a material to compressive stress, resulting in reduction of volume. ... A liquid will usually assume the shape of its container. ... Physical compression is the result of the subjection of a material to compressive stress, resulting in reduction of volume. ... A gas is one of the five main phases of matter (after solid and liquid, and followed by plasma and Bose-Einstein Condensate) and, that subsequently appear as a solid material is subjected to increasingly higher temperatures. ...

The process is performed by forcing clean, bubble-free brake fluid through the entire system from the master cylinder(s) to the calipers of disc brakes or the wheel cylinders of drum brakes). The brake bleeder is normally mounted at the highest point on each cylinder or caliper. Brake bleeding can be done easily by two persons working together and doesn't require much technical expertise besides a basic knowledge of brakes and car hydraulics. One wheel at a time, the brake bleeding valve for that wheel is opened while a drain hose is attached to that valve and immersed into a pool of brake fluid. The assistant then pumps the brake pedal. In this manner, fresh fluid is forced through the system into that wheel's caliper or wheel cylinder, and any old, dirty, water-saturated or bubble-entrained fluid is expelled from the system. When the fluid from the caliper or wheel cylinder runs clean, clear, and bubble-free, the brake bleeding valve is closed and the drain tube removed. The process is then repeated for the remaining wheels. During the entire process, the brake fluid reservoir must be kept full of fresh fluid lest new air bubbles be introduced into the brake system. The master cylinder is a hydraulic control device that converts physical pressure (commonly from a drivers foot) into hydraulic pressure to operate other device(s) in the hydraulic system. ... Close-up of a disc brake on a car On automobiles, disc brakes are often located within the wheel disc brake is a device for slowing or stopping the rotation of a wheel. ... A drum brake is a brake in which the friction is caused by a set of shoes or pads that press against the inner surface of a rotating drum. ...

More sophisticated automatic systems allow brake fluid to be forced under pressure from the brake fluid reservoir into the entire system. Using these devices, no assistant is required.

Also, don't forget to start with the wheel furthest from the master cylinder; almost always the rear passenger wheel. Then go to the rear driver's wheel, front passenger wheel, and finally the driver's front wheel.

External links

• [1] - One of many useful links on the web for amateur mechanics.
• [2] - A page written by professional racers on maintaining and improving brake performance