Removal of air from a hydraulic drive of brakes

Bleeding the brakes is necessary to remove air from the hydraulic drive, which significantly reduces the effectiveness of the working brake system. Air can get into the hydraulic drive due to depressurization of the system during the repair or replacement of individual components, as well as when replacing the brake fluid. The presence of air in the brake actuator is indicated by an increased stroke of the brake pedal and its «softness».

Before removing air from the brake system, make sure that all brake drive units and their connections are tight, clean the cover and the surface around the reservoir cap, fill the reservoir with liquid «Neva» or «Tom» up to the mark «MAX». Then the fittings are thoroughly cleaned to remove air and the protective caps are removed from them. It is not recommended to use the fluid drained from the system to fill the reservoir, as it is saturated with air, has a lot of moisture and may be contaminated.

Air is removed from the system first from one circuit, then from another, starting with the wheel cylinders of the rear brakes.

Put on the head of the fitting 1 (pic. 114) rubber hose 2 for draining the liquid, and its free end is lowered into a transparent vessel 3, partially filled with liquid. By sharply pressing the brake pedal 3-5 times at intervals of 2-3 s, the fitting is unscrewed by 1/2-3/4 turn with the pedal depressed. Continuing to press the pedal, the liquid in the system is displaced along with air through the hose into the vessel. After the brake pedal reaches the front end position and the outflow of fluid through the hose stops, wrap the air outlet fitting to failure. Repeat these operations until no more bubbles come out of the hose.




While holding the pedal down, tighten the fitting to failure and remove the hose. Wipe dry the fitting and put on a protective cap. Then the operations are repeated for other wheels, first on the second wheel of the same circuit, and then successively on both wheels of another circuit. When air is removed, the presence of liquid in the tank is monitored, preventing its bottom from being exposed, since air enters the system again. If there is no air in the brake actuator, the brake pedal should travel about 1/2 of its full travel. To eliminate the influence of the vacuum booster on the pumping of the brakes, the removal of air is carried out with the engine off.

If there is no brake fluid in the hydraulic drive, then fill the system as follows:

• pour brake fluid into the reservoir;
• unscrew 1.5-2 turns of the fitting on the cylinders of all wheels;
• sharply pressing the brake pedal and gently releasing it, wrap the fitting as fluid flows out of them. Then the brake system is bled. When removing air on a car whose brake system has worked for a long time, the fluid is replaced with a new one.