Attention! Brake fluid is poisonous. If it comes in contact with skin, wash it off immediately. If fluid gets into eyes, seek medical attention. Certain types of liquids are flammable and can ignite if they come into contact with hot parts. When servicing hydraulic systems, it is recommended to consider that the working fluid may be flammable, and to take fire safety measures so. as if you were dealing with gasoline. Operating fluids damage paintwork and plastics. If liquid comes into contact with such surfaces, immediately wash it off with plenty of clean water. Working fluids are also hygroscopic (actively absorb moisture from the air). Therefore, liquids with a significant shelf life may contain impurities and should not be used. When filling the hydraulic system, always use the recommended type of fluid and drink it from a sealed container immediately after opening.
Attention! On models with ABS Ic and without ASC+T) after disconnecting the high pressure lines connecting the hydraulic unit to the master cylinder and accumulator (if it exists) the system must be bled at a specialized service station. These stations have special equipment for the safe pumping of such systems.
Basic information
1. Reliable operation of any hydraulic system is possible only after the removal of air from all circuits and components. This is achieved by pumping the system.
2. When primed, add only clean working fluid of the recommended type to the system. Never fill with fluid that has been drained from the system Before starting work, make sure that you have enough working fluid.
3. If you suspect the presence of an unspecified fluid in the hydraulic system, then in this case it is necessary to flush the circuits and components of the brake system with a clean working fluid of the recommended type, and also replace all seals.
4. If hydraulic fluid is leaking or air is trapped in the hydraulic system due to leakage, repair the problems before proceeding with the following procedures.
5. Install the car on a horizontal platform. Stop the engine. Engage first gear or reverse gear. Then chock the wheels and release the parking brake.
6. Make sure all piping and hoses are in good condition, connections and air bleed screws are tight. Clean the dirt around the bleed screws.
7. Turn away a cover of a reserve tank of the main cylinder. Pour brake fluid into the reservoir up to the mark "MAX". Install tank cap (without wrapping it). Do not forget that to prevent air from entering the system during pumping, it is necessary to maintain the fluid level in the reservoir at least above the mark "MIN".
8. You can purchase one of the kits designed for self-bleeding the brakes. It is recommended to always use such a kit, as it greatly simplifies the bleeding process and reduces the risk of expelled air and drained fluid returning to the system. If you do not have such a set, use the main pumping method, which involves the participation of two people, which is detailed below.
9. If you will use a bleeding kit, prepare the car for bleeding (see above) and follow the manufacturer's instructions. Bleeding procedures may differ depending on the type of kit. Below is only the basic scheme of its implementation.
10. To remove air from the system in any way, it is necessary to follow the sequence specified in p.p. 11 and 12.
Bleeding the brake system
Pumping sequence
11. When disconnecting individual components in any part of the system, taking precautions to reduce leaks, bleed only that part of the system.
12. If it is necessary to bleed the entire system, follow the procedures in the following order:
- A) Rear right brake
- 6) Rear left brake
- V) Front right brake
- G) Front left brake
Attention! Models with ABS (with or without ASC+T system) after bleeding the brake system, you should contact a specialized service station as soon as possible to check the operation of the brake system.
The main method of pumping with the participation of two people
13. Prepare a clean glass container, a rubber or plastic tube of a suitable length, which must be pulled over the screw for bleeding, and a ring wrench to turn the screw. You will also need an assistant.
14. Remove the dust cap from the first (according to the above sequence) bleed screws. Put the key and tube on the screw. Lower the free end of the tube into a container and pour so much liquid into it that its level is higher than the end of the tube.
15. When performing this procedure, it is necessary to maintain the fluid level in the reservoir of the master cylinder, at least not below the mark "MIN".
16. Ask the assistant to fully squeeze the brake pedal several times to pressurize the system and hold it in the depressed position.
17. With the pedal depressed, unscrew the air bleed screw (about one turn) for the exit of liquid and air under pressure into the container. The assistant should keep the pedal depressed, pressing it to the floor if necessary, and not release it without your command. When fluid stops flowing from the tube, tighten the screw and have an assistant slowly release the pedal. Check the fluid level in the reservoir.
18. Repeat the operations indicated in p.p. 16 and 17 until the liquid flowing out of the bleed screw no longer contains air bubbles. If the master cylinder has been emptied and then refilled with brake fluid and air continues to escape from the first (in the run sequence) cylinder, then before continuing the pumping procedure, it is necessary to pause (about 5 seconds) to fill the channels of the master cylinder.
19. Once the air bubbles in the fluid stream have disappeared, securely tighten the bleed screw. Then remove the handset and key. Install the dust cap. Do not apply excessive force when tightening.
20. Repeat the bleeding procedure for the remaining working cylinders (in the run sequence) until the air is completely removed from the system and the brake pedal becomes "tough".
Bleeding using a check valve kit
21. In accordance with the name, such a set contains a tube with a shut-off valve. which is designed to prevent the return of air and fluid displaced from the system back into the system. Such a kit may include a transparent container that can be conveniently positioned so that air bubbles exiting the tube can be observed (pic. 2.21).
22. This set must be connected to the bleeder screw, and then the screw must be removed. After that, you should return to the driver's seat and depress the brake pedal smoothly and evenly, and then slowly release it. Repeat the procedure until the air bubbles in the escaping liquid disappear.
23. When using such a convenient tool, do not forget to control the liquid level in the tank, which should always be at least (at least) marks "MIN".
Bleeding with a pressure bleed kit
24. Such a kit is usually powered by a container of compressed air, such as a spare tire. However, please note that the pressure will probably need to be lowered to a lower value than usual (see instructions for use supplied with the equipment).
Note. BMW does not allow operation at pressures exceeding 2 bar.
25. Attach a sealed container with the liquid under pressure in it to the reservoir of the brake system. After that, you can start pumping by simply unscrewing the screws of the working cylinders in turn (in the above sequence). Release the liquid until no more air bubbles come out of the outlet stream.
26. This method has the advantage that the large fluid container provides additional protection against air entering the system during pumping.
27. Pressurizing is especially effective when used to "complex" systems or when pumping the entire system during a scheduled fluid change.
All ways
28. After removing air from the system and restoring "pedal stiffness" wash off spilled liquid. Tighten the bleed screws securely and put the dust caps on them.
29. Check the fluid level in the tank and top up if necessary (cm. "Weekly check").
30. Discard the fluid drained from the system. It cannot be reused.
31. Check the feel of the brake pedal. Feeling "softness" throughout the pedal stroke means that there is air in the system and therefore further bleeding is required. If you repeated the bleeding procedure several times, but did not achieve a satisfactory result, then this may indicate wear on the master cylinder seals.