Before bleeding the brake system, make sure that all brake drive units and their connections are tight, check and, if necessary, fill the reservoir with brake fluid to the normal level. Then thoroughly clean the air bleeding nipples from dirt and dust and remove their protective caps.
Place a rubber hose (Fig. 6-7) onto the head of the fitting to drain the fluid, and lower its free end into a transparent container partially filled with brake fluid.
Press the brake pedal sharply 3-5 times, with intervals of 2-3 seconds between presses, and unscrew the nipple by 1/2-3/4 of a turn with the pedal pressed. Continuing to press the pedal, force the fluid together with the air through the hose into the container. After the brake pedal reaches the extreme forward position and the fluid flow through the hose stops, screw the air bleed nipple all the way in. Repeat these operations until all air bubbles come out of the hose. Then, holding the brake pedal pressed, screw the air bleed nipple all the way in and remove the hose. Wipe the nipple dry and put on the protective cap.
Perform all the above operations through the upper nipples first on the right rear wheel farthest from the master cylinder, then clockwise: left rear wheel, left and right front wheels. This will remove air from one circuit. To bleed the other circuit, use the lower nipples on the cylinder block of the left and right front brakes. In this case, air removal can begin from the right or left wheel.
When removing air, maintain a normal fluid level in the brake hydraulic drive reservoir. If there is no air in the drive, the brake pedal should not move more than 1/2-3/4 of its full travel.
To eliminate the influence of the vacuum booster and pressure regulator on the bleeding of the brake hydraulic drive, bleed the air with the engine off and the rear wheels loaded (hanging the rear of the vehicle is not allowed).
If the brake fluid has been completely drained from the system, then before removing the air:
- loosen the air bleed nipples on the cylinders of all wheels by 1.5-2 turns;
- sharply pressing the brake pedal and smoothly releasing it, tighten the nipples as the fluid flows out of them. Then bleed the brake hydraulic drive as described above.
If, even after prolonged removal, air continues to escape from the hose into the vessel in the form of bubbles, it means that it is entering the system through damage in the pipelines, due to insufficient tightness of the connections, or due to a malfunction of the main or wheel cylinders.
When bleeding air from a vehicle whose brake system has been in use for a long time, replace the fluid in the system with new fluid.
The liquid suitable for further use must be carefully filtered and then allowed to settle in a hermetically sealed container.