WARNING
Brake fluid is poisonous - be careful when working with it. In addition, it dissolves paint and plastic, so if the fluid gets on the car's paintwork, wash it with plenty of water.
Fig. 14.11. Installing a container with brake fluid 30 cm above the bleed nipple when removing air from the front brake caliper
During the bleeding process, the reservoir must be constantly filled with fresh brake fluid up to the "MAX" mark. Make sure that the fluid level does not fall below the "MIN" mark, otherwise air will enter the system again through the filler hole. When bleeding, place the brake fluid container 30 cm above the bleed nipple - the bleed nipple will be under fluid pressure, and air will not be able to penetrate through the nipple thread into the brake system (Fig. 14.11).
SEQUENCE OF WORKS
Fig. 14.12. Disconnecting the contact connector (1) of the brake fluid level sensor from the plug (2)
1. Disconnect the central contact connector 1 (Fig. 14.12) of the brake fluid level sensor from plug 2. Unscrew the plug.
2. Bleeding sequence: front left wheel, rear right wheel, front right wheel, rear left wheel.
3. Remove the protective caps and clean the bleed nipples.
Fig. 14.13. Location of the bleed nipple with a clean transparent hose attached to it
4. Attach a clean transparent hose to the bleed nipple and lower the other end into a container partially filled with brake fluid (Fig. 14.13).
5. Loosen the bleed nipple by 1/2–1 turn. The assistant should slowly press the brake pedal, while the fluid in the system together with the air is forced out through the hose into the container. Then quickly release the pedal to its original position.
6. Wait approximately 3 seconds for the master cylinder to fill with brake fluid.
7. Repeat these steps until air stops escaping from the hose. Keep the brake pedal depressed.
8. Screw the bleed nipple all the way in and release the brake pedal. Remove the hose from the bleed nipple and add brake fluid to the reservoir.
9. Repeat this operation on all wheels.
10. Add brake fluid to the reservoir up to the "MAX" mark, tighten the cap and connect the contact connector.
11. Carefully test the brakes during a test drive.
TECHNICAL DICTIONARY
Brake fluid
Brake fluid is a mixture of glycol, polyglycol ether and several other components. It is a yellowish liquid, very toxic and aggressive towards the car's paintwork, but it does not destroy metal and rubber parts. The working range in which the liquid retains its properties is from -40 to +270°C.
Brake fluid is hygroscopic, i.e. it absorbs moisture from the air, so it should be stored in tightly sealed containers. Moisture can penetrate into the brake fluid poured into the hydraulic drive of the brake system, for example, from the air through the reservoir or microscopic leaks on the brake pipes and hoses. When water gets into the brake fluid, its properties change. Absorption of moisture leads not only to corrosion of metal parts of the brake system, but also significantly lowers its boiling point. Even with a water content of 2.5% in the brake fluid, its boiling point is approximately 150°C. This is especially dangerous during intensive braking, since in this case the brakes can heat up very much, and steam bubbles can form in the brake fluid near the hot brakes. The bubbles are compressed, as a result of which the brake pedal travel increases, and in some cases the pedal can even fall through. In this case, quickly pumping up the pressure with the brake pedal will help. This effect is especially dangerous after intensive braking when stopping the car, since due to the lack of oncoming air flow, the brake mechanisms heat up even more and such a high temperature remains for a long time.
Therefore, for safety reasons, change your brake fluid regularly. If you regularly have your car serviced at a car repair shop, changing the brake fluid is part of your routine maintenance; if you service your car yourself, you need to change the brake fluid at least once every two years.
Disposal of old brake fluid
The brake fluid used in the hydraulic brake drive is poisonous, so if it gets on your skin, you should immediately wash it off with plenty of water. If the fluid gets into an open wound or inside your body, you should immediately consult a doctor.
Brake fluid does not damage metal and rubber parts, but is aggressive to the car's paintwork. If you have drained the brake fluid from the system, it is not recommended to use it again. Do not use brake fluid from a container that has been open for a long time. Dispose of old brake fluid in specially designated places.