- Open-end wrench for the air bleed nipple. For example, HAZET 1968-7.
- Transparent plastic hose with an internal diameter of 6 mm and a container for collecting brake fluid.
- About 1.0 liter of brake fluid.
Do not use DOT 5 brake fluid. Do not refill the system with used fluid.
Follow the rules for handling brake fluid, refer to Section Brake fluid - basic information and safety precautions.
Protect the environment, never pour out used oil or dispose of it with household waste. Local authorities should inform about the location of the nearest collection points for used materials.
Brake fluid absorbs moisture through the pores of the brake hoses and the ventilation holes of the fluid reservoir. As a result, the boiling point of the brake fluid decreases during operation. With a significant load on the brakes, this can lead to the formation of steam bubbles in the brake pipes, which reduces the effectiveness of the brakes. Therefore, it is necessary to replace the brake fluid every 2 years.
1. Follow the rules for handling brake fluid as described in Section Brake fluid - basic information and safety precautions.
At the service station, air from the brake hydraulic system is usually removed using a special device. The device supplies brake fluid to the reservoir under a pressure of 2.0 bar. This operation can be performed without using a special tool. In this case, air is removed from the brake system by rocking movements of the brake pedal. The operation is performed with the help of an assistant.
If air has penetrated into the ABS hydraulic unit, it is recommended to remove it at a service station. This occurs if there is a leak in the hydraulic unit or if one chamber of the brake fluid reservoir is empty or if you forgot to add fluid when removing air from the system.
2. Mark the fluid level on the reservoir. After replacing the fluid, restore the previous fluid level. This will prevent the reservoir from overflowing with fluid when replacing the brake pads.
3. Suck out the liquid from the tank to a level of 10 mm.
4. Fill the reservoir with fresh brake fluid up to the MAX mark.
Carefully open the bleed nipples without unscrewing them. It is recommended to spray the nipples with rust solvent about two hours before opening. If any nipple does not unscrew, you must contact a service station.
Air removal sequence
1. Rear right support.
2. Rear left support.
3. Front right support.
4. Front left support.
5. Attach a clean hose to the nipple of the right rear brake cylinder and place a suitable container underneath.
6. Ask an assistant to slowly press the brake pedal until you feel resistance.
7. Keeping the brake pedal depressed, loosen the union with the open-end wrench "1" on the right rear caliper. Close the union when the pedal touches the floor. Ask the assistant to release the pedal.
8. Repeat the above procedure as many times as necessary to ensure that the liquid coming out is free of bubbles. Fresh liquid is recognizable by its light color.
9. Lightly tighten the fitting. The tightening torque depends on the thread diameter: a fitting with a diameter of 7 mm is tightened with a torque of 5 N·m, a fitting with a diameter of 11 mm with a torque of 15 N·m.
10. Similarly, in the order indicated above, pump out the brake fluid from the other calipers.
While removing air, add liquid to the reservoir. It should not be completely empty. Otherwise, air will enter the system.
11. After replacing the brake fluid, press the brake pedal and check its free travel. It should not exceed 1/3 of the total pedal travel.
12. Cars with manual transmission: Since the clutch drive operates on brake fluid, the fluid in the clutch hydraulic system is replaced in the manner described above.
13. Before replacing the brake fluid, fill the reservoir to the marked level.
14. Screw the lid onto the tank.
- Are the brake hoses secured?
- Is the brake hose secured in the holder?
- Are the air bleed nipples tightened?
- Is there enough brake fluid?
With the engine running, check for leaks. To do this, press the brake pedal with a force of 200–300 N (20–30 kg) for 10 s. The pedal should not weaken. Check all connections for leaks.
15. Finally, brake several times on a road with sparse traffic. At least once, perform full braking, which activates the ABS, in particular on the ground. The operation of the ABS is felt by the pulsations of the brake pedal.
(The original source of the article is on the website BMWMAN.ru)