The air that got into the brake hydraulic drive when replacing pipelines, hoses, sealing rings or when the system is leaking causes an increase in the brake pedal stroke, its "softness" and significantly reduces the effectiveness of the brakes.
Before removing air from the brake system, make sure that all brake drive units and their connections are tight, check and, if necessary, fill the tank to a normal level with liquid "Neva" or "Tom". Then carefully clean the fittings for removing air from dirt and dust and remove the protective caps from them.
Air is removed first from one circuit, then from another, starting each time with the wheel furthest from the master cylinder. The pumping of the hydraulic drive is carried out in the following order:
- remove the front wheels; put on the head of the fitting 1 (pic. 143) a rubber hose, and the other end of the hose is lowered into a transparent vessel partially filled with brake fluid;
- sharply pressing the brake pedal 3-5 times with intervals between pressing 2-3 s, unscrew the fitting 1 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;
- its forward position and the outflow of liquid through the hose will stop, wrap the air outlet fitting to failure. These operations are repeated until the exit of bubbles from the hose stops;
- while holding the pedal in the depressed position, wrap the fitting to failure and remove the hose, wipe the fitting dry and put on a protective cap;
- repeat operations for other wheels, first on the second wheel of the same circuit, and then sequentially on both wheels of the second circuit.
When removing air, maintain a normal fluid level in the reservoir of the hydraulic brake drive. After complete removal of air, the brake pedal should not pass more than 1/2-3/4 of its travel.
To eliminate the influence of the pressure regulator on the pumping of the brakes, the air is removed with the rear wheels loaded (hanging the rear of the car is not allowed).
If the liquid has drained completely, then before removing air from the system:
- unscrew 1.5-2 turns of the fitting on the cylinders of all wheels;
- sharply pressing the brake pedal and slowly releasing it, wrap the fitting as fluid flows out of them. Then the drive is pumped, as indicated above.
If, even after prolonged removal, air continues to exit the hose in the form of bubbles, then it enters the system through damage in the pipelines, due to insufficient tightness of the connections or due to a malfunction of the master or wheel cylinders.
If the bleeding is performed on a car whose brake system has worked for a long time, then the fluid in the system is replaced with a new one.