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 reservoir with brake fluid to a normal level. Then carefully clean the bleeder fittings from dirt and dust and remove the protective caps from them.
Put a rubber hose on the head of the fitting (pic. 6-7) to drain the fluid, and lower its free end into a transparent vessel partially filled with brake fluid.
By sharply pressing the brake pedal 3-5 times, with intervals between pressing 2-3 s, unscrew the fitting by 1/2-3/4 turn with the pedal depressed. Continuing to press the pedal, force the liquid along with the air through the hose into the vessel. After the brake pedal has reached its full forward position and fluid has stopped flowing through the hose, tighten the air outlet fitting until it stops. Repeat these operations until the air bubbles are completely out of the hose. Then, while holding the brake pedal down, tighten the air outlet fitting until it stops and remove the hose. Wipe dry the fitting and put on the protective cap.
All the above operations are carried out through the upper fittings, first on the right rear wheel farthest from the master cylinder, then clockwise: the left rear wheel, the left and right front wheels. This will remove air from one circuit. To bleed another circuit, use the lower fittings on the cylinder block of the left and right front brakes. In this case, the removal of air can be started from the right or left wheel.
When removing air, maintain a normal fluid level in the brake fluid reservoir. In the absence of air in the drive, the brake pedal should not pass 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 hydraulic drive of the brakes, carry out the removal of air with the engine off and the rear wheels loaded (hanging the rear of the car is not allowed).
If the brake fluid has been completely drained from the system, before bleeding:
- unscrew the air bleed fittings on the cylinders of all wheels by 1.5-2 turns;
- sharply pressing the brake pedal and slowly releasing it, tighten the fittings as fluid flows out of them. Then bleed the hydraulic brakes 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 enters 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 on a vehicle whose brake system has been in operation for a long time, replace the fluid in the system with a new one.
The liquid suitable for further use must be carefully filtered and then allowed to settle in a hermetically sealed vessel.