1. Check all brake line connections for leaks. Check for worn hoses, cracks, and cuts.
2. If you have any doubts about the brake caliper or wheel cylinder, you should inspect them for signs of fluid leakage.
3. Prepare a clean container, a piece of rubber tubing that will fit tightly onto the drain valve, and brake fluid.
4. First bleed the master cylinder (see Bleeding air from the master cylinder).
5. Loosen the nut where the hydraulic line connects to the master cylinder.
6. Have an assistant slowly press the brake pedal to the floor, which will force the air in the master cylinder out through the loose connection.
7. With the pedal fully depressed, tighten the connection. Release the pedal. The pedal must not be released until the connection is tightened, otherwise air may enter the cylinder.
8. Repeat this procedure until no more air comes out of the cylinder.
9. Bleed the hydraulic systems separately, starting with the longest line (rear).
10. To bleed the brake system, clean the surfaces near the bleed valves. Remove the rubber cap from the bleed valve and place a piece of rubber tube on the nipple.
11. Place the other end of the tube in a container filled with enough brake fluid to keep the end of the tube immersed in it during bleeding.
12. Open the bleed valve about 3/4 of a turn and have an assistant slowly press the brake pedal to the floor and hold it there.
13. Close the drain valve and release the pedal.
14. Continue this operation until air bubbles stop coming out.
Material taken from a web resource (MERCEDESMAN.ru)
15. When bleeding the system, periodically check the fluid level in the tank. It must be filled to the top, otherwise air will get into the system again. Do not add fluid to the tank that has already been pumped out of the system.
16. Repeat the entire procedure for the second rear wheel.
17. Bleeding the front brake system is carried out in a similar manner.
18. Fill the master cylinder with fluid so that its level in the tank is approximately 6-7 mm below the top edge.
19. Check the operation of the brake fluid level indicator by pressing the black rubber bulb at the top of the reservoir (with ignition on). The light on the dashboard should come on.
20. Check the feel of the brake pedal: it should be firm and not give a feeling of dips ("viscous"), which is a sign of the presence of air in the hydraulic drive.