Attention! Hydraulic fluid is poisonous. If the liquid comes into contact with the skin, immediately wash it off with water. If liquid gets into eyes, seek medical attention immediately. Some types of fluid are flammable and ignite on contact with hot objects. When working with the hydraulic system, observe fire safety measures. In addition, hydraulic fluid can ruin a car's paintwork and dissolve some plastics. If liquid spills onto plastic or paint, wash it off immediately with water. And finally, this liquid is hygroscopic (absorbs moisture from the air), so don't use old fluid. When replacing or topping up, use only the recommended type of fluid and store it in a sealed container.
Note. BMW recommends using a pressure bleeder to bleed the hydraulic system.
Basic information
1. The operation of any hydraulic system is possible only in the absence of air in its circuit. This is achieved by removing air (pumping) hydraulic systems.
2. When bleeding the hydraulic system, add only clean, fresh fluid of the recommended type. Never reuse liquid. Before starting work, purchase the required amount of liquid.
3. If there is even a small chance that another type of fluid is filled in the clutch or brake hydraulic system, the components of the brake system and clutch drive must be flushed with the recommended type of fluid and all cuffs and hydraulic seals should be replaced.
4. If the fluid level in the reservoir is too low due to leaks and air has entered the hydraulic system, repair the fluid leak before pumping.
5. Apply the parking brake for easier access, then raise the front of the vehicle and place it on secure stands (cm. "Lifting and placing the car on supports").
6. Turn out screws and remove protection of a case of the engine for simplification of access to the case of a transmission.
7. Make sure clutch hoses and lines are secure and hydraulic bleed screw is tight. The clutch bleed screw is located on the rear side of the clutch slave cylinder. Access to the screw is carried out from under the car, on the left side. Clean the screw and the area around it from dirt (pic. 6.7).
8. Remove the cap from the hydraulic reservoir and add fluid to the MAX mark. Replace the cover and tighten it slightly. Make sure that during pumping the liquid level in the tank does not fall below the MIN·mark. Keep in mind that the reservoir feeds both the hydraulic clutch and the brake system.
9. A pressure bleeder is recommended to bleed the system. Alternatively, you can use any brake bleeder tool without a second person (You can purchase this tool from an auto parts store). Such devices greatly facilitate the pumping process, and also reduce the risk of air entering the hydraulic system during pumping. If you do not have such a device, you can use the method of pumping the hydraulic system together (This method is described in more detail below).
10. If you are using a bleeder or other tool, prepare the vehicle (as described above) and bleed the system following the tool manufacturer's instructions, as the procedure for bleeding depends on the type of tool being used. Bleeding methods using the most common fixtures are described below.
Pumping
Main Method (pumping together)
12. Prepare a transparent glass container and a piece of rubber tube, which is tightly put on the screw for pumping, as well as a wrench to remove the screw. For work you need an assistant.
13. Remove the cap from the bleed screw (if it exists). Put the wrench and tube on the screw and lower the other end of the tube into the glass container. Pour clean liquid into the container so that the end of the tube is immersed in it.
14. During the entire bleeding procedure, monitor the fluid level in the master cylinder reservoir and do not allow it to drop below the MIN risk.
15. Ask an assistant to press the clutch pedal several times, then press the pedal and do not release it.
16. With the clutch pedal depressed, loosen the bleed screw approximately one turn and let the fluid with air drain into a container. The assistant must keep the clutch pedal depressed and not release it without your command. After fluid stops flowing out, tighten the screw and have an assistant release the pedal slowly. Add fluid to the master cylinder reservoir.
17. Repeat the procedure described in p.p. 15 and 16 so far. until the liquid flowing out of the tube no longer contains air bubbles.
18. After bleeding is complete, tighten the screw securely. Don't overtighten it.
19. Temporarily remove the hose from the screw and set the container aside.
20. Turn away two nuts of fastening and take out the working cylinder of coupling from the case of a transmission, without allowing an excessive tension of a hose.
21. Reattach the tubing to the bleed screw and dip the other end of the tubing into the container of liquid.
22. Position the cylinder so that the screw is facing vertically upwards and back it out approximately one turn. Slowly push the plunger into the cylinder until all air bubbles are expelled from the cylinder.
23. While holding the plunger in the recessed position, tighten the bleed screw.
24. Let the pusher slowly return to its original position. Do not allow the plunger to move quickly, as this can lead to air entering the working cylinder.
25. Remove the tube and wrench from the screw and place the protective cap over the screw.
26. Install the working cylinder in place and tighten the fastening nuts to the required torque.
Bleeding with a check valve
27. As their name suggests, these devices consist of a hose that has a check valve built into it to prevent air and fluid from flowing back into the hydraulic system. Some of these devices include a transparent container, which makes it easier to observe the air bubbles escaping from the hydraulic system.
28. The device is put on the screw for pumping, which is then turned away. After that, you need to sit in the driver's seat and slowly press and release the clutch pedal until then. until no more air comes out of the hydraulic system.
29. Keep in mind that the bleeding process with this tool is so easy. that it is very easy to forget about the need to maintain the fluid level in the master cylinder reservoir.
Pumping under pressure
30. Such devices usually use compressed air from the spare tire for their work. In some cases, the air pressure in the tire needs to be reduced from normal. Read the instructions for using this device carefully.
31. The device includes a container with liquid under pressure. After the fluid container is connected to the master cylinder reservoir, the bleed screw must be removed and the fluid allowed to flow out until then. until no more air bubbles come out.
32. This method is preferred because this tool has a large fluid reservoir that prevents the fluid level in the master cylinder reservoir from dropping.
All Methods
33. If air still remains in the system after bleeding, remove the working cylinder (see paragraph 4), without disconnecting the hose from it, push the piston and turn the cylinder so that the bleed screw is facing up. Repeat the pumping procedure.
Note. Fix the piston of the working cylinder so that it cannot move out of the cylinder.
34. After priming is complete, wipe off all traces of spilled fluid with a rag, make sure the bleed screw is securely tightened, and put the protective cap on the screw.
35. Check the fluid level in the reservoir of the main cylinder and bring it to the required (cm. "Weekly checks").
36. Discard the liquid that remains after pumping. Never reuse this fluid.
37. Check the operation of the clutch pedal. If an elastic resistance is felt when pressing the pedal, this indicates the presence of air in the hydraulic system and the need for additional pumping. If the hydraulic system does not bleed after several attempts, this indicates excessive wear on the master or slave cylinder seals.
38. After finishing work, install the engine crankcase protection and lower the car.