Replacing brake fluid and bleeding the brake system (BMW 7 Series E38)

General information

Brake fluid is hazardous to health. Do not suck it out with your mouth through a hose. Store brake fluid only in a container that is inaccessible to children.

1. Brake fluid is hygroscopic, i.e. it has the ability to absorb moisture, as a result of which its boiling point decreases over time, which, under significant load on the brakes, can lead to the formation of steam bubbles in the brake lines and reduce the effectiveness of the brakes.

2. To change the brake fluid, you will need the help of an assistant, but at a service station this procedure is usually carried out using a special device. When bleeding the brake system, the car must be parked on a level horizontal surface.

Replacing brake fluid and bleeding the brake system

1. Turn off the ignition and disconnect the ABS actuator wiring connector.

2. Remove the cap from the brake fluid reservoir (see illustrationsEngine Compartment Components).

3. Mark the current brake fluid level on the tank wall with a felt-tip pen, so that you can avoid exceeding it when replacing the brake pads. Pump out the brake fluid from the tank, leaving a layer of liquid at the bottom of about 10 mm.

Do not remove all the fluid from the reservoir, otherwise air will enter the hydraulic drive of the brake and clutch system.

4. Fill in fresh water tank brake fluid up to the "MAX" mark.

5. Thoroughly clean and remove the protective caps from the bleed nipples.

6. Attach one end of a clean, transparent hose to the rear right brake bleeder nipple and insert the other end into a container to collect the brake fluid. Pour some brake fluid into the container and make sure that the end of the hose is submerged in it at all times. Also, raise the container at least 30 cm above the bleed nipple to ensure pressure and prevent air from entering it.





Connecting the bleeding device to the rear brake mechanism.

7. Ask an assistant to press the brake pedal sharply 3-5 times at intervals of 2÷3 seconds and release the nipple by 1/2÷3/4 of a turn with the pedal depressed. After the brake pedal hits the floor, tighten the nipple. Remove your foot from the pedal. Repeat this process to pump out the old brake fluid (until a new one appears, which can be recognized by its light color).

If the liquid layer at the bottom of the tank is less than 10 mm, the system will have to be pumped.

8. Tighten the bleed screw, close its protective cap and add new brake fluid to the reservoir.



9. In the same way, pump out the old brake fluid sequentially from the remaining calipers in the following order: rear left, front right, front left.

The drained brake fluid must in any case be clean and without air bubbles.

10. Adjust the brake fluid level according to the previously applied mark

11. Press the brake pedal and check its free travel. Make sure that the brake pedal does not "sink" when you press it - the free travel of the pedal should be no more than 1/3 of its full travel.

12. Check the brakes on a road with light traffic. To do this, you should perform at least one strong braking, checking the ABS at the same time. A sign of proper ABS operation is pulsation of the brake pedal when braking.

The effect of ABS is best seen on unpaved roads.