Before bleeding the brake system, make sure that all brake drive units and their connections are tight, check and record the fluid level in the reservoir and, if necessary, fill the reservoir to the "MAX" level with brake fluid. After bleeding, the fluid should be at the same level. If necessary, add fluid or drain excess using a bulb. Then thoroughly clean the air bleed nipples from dirt and dust and remove their protective caps.
Place a rubber hose on the head of the fitting (figure 6-7) to drain the liquid, and lower its free end into a transparent container partially filled with liquid.
Figure 6-7. Bleeding air from the hydraulic brake drive.
Press the brake pedal and unscrew the nipple by ½-3/4 of a turn. Continuing to press the pedal, force the fluid and air through the hose into the container. After the brake pedal reaches the extreme forward position and the fluid stops flowing through the hose, 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 first on the right rear wheel, then on the left front wheel. This will remove air from one circuit. To bleed the other circuit, repeat the bleeding in the following sequence: left rear - right front wheel.
When bleeding 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 go more than half of its full travel.
Remove air when the rear wheels are 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 as a result of 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.