The appearance of air may be caused by damage to the brake pipes (usually at the points of connection or attachment to the body), loss of tightness of brake hoses (mechanical damage or loose connection), damage to the cuffs in the working and/or main brake cylinders, as well as any repair of brake system components.
Air entering the system reduces its efficiency and, therefore, driving safety.
Before performing the air removal operation, thoroughly clean the areas around the bleed nipples and the brake fluid reservoir cap, and add brake fluid to the reservoir.
Select an elastic, preferably transparent tube that fits tightly onto the bleed nipple (usually they take tubes from medical blood transfusion systems).
If the work was carried out only with the brake of one wheel, then it is enough to bleed only this part of the hydraulic drive. In other cases, the following sequence should be followed: rear right wheel, rear left, front right, front left.
Place the tube on the bleed nipple of the wheel cylinder, lower the other end of the tube into the container (also preferably transparent) capacity of about 200 ml, half filled with brake fluid.
The simplest method is when a single person creates pressure in the system by pressing the brake pedal several times and then holding it in the depressed position. The second person unscrews the fitting.
Attention! Unscrew the nipple only when the pedal is pressed!
When the nipple is unscrewed, the brake fluid with air comes out through the hose into the container. Air bubbles rise to the surface of the liquid in the container, and the liquid itself acts as a valve, preventing air from passing back into the system if the pedal is accidentally released. Tighten the nipple and create pressure again. Bleed until air stops coming out of the system. Bleeding for all wheels is done in the same way. Constantly add brake fluid to the reservoir; if the liquid level in it drops significantly, then you will have to repeat the bleeding. If you do not have an assistant, you need to select a rack of such a length that it can be used to fix the pedal in the pressed state, resting one end on the pedal and the other on a convenient place in the body (for example, sitting).
A more complex method is one in which the pressure in the system is created by feeding compressed air into the tank at a pressure of no more than 1 kg/m². There is no need to press the pedal, all other actions are similar to those described above.
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The liquid drained from the system can be reused only if it is transparent and its period of use does not exceed 1.5 years (and only after filtering).
When replacing brake fluid, you should do the same as when removing air from the system. The criterion for stopping bleeding should be the appearance of fresh fluid in the transparent tube (it is more transparent than the old one).
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