This is because brake fluid is very hygroscopic. It absorbs moisture from the air, which, in addition to causing corrosion of parts of the brake system, lowers the boiling point of the fluid itself, and this can lead to brake failure during frequent heavy braking. Do not reuse the drained fluid: it is contaminated, saturated with air and moisture. Always add only new fluid of the same brand to the system as the fluid that was filled before.
Before changing the brake fluid, check the tightness of the hydraulic drive (see «Checking the tightness of the hydraulic drive of the brakes») and troubleshoot.
Brake fluid must be changed with an assistant. It is convenient to work by installing the car on an inspection ditch or overpass (no need to remove wheels).
You will need: key «at 11» for pipelines, brake fluid, rubber or transparent hose, transparent vessel, syringe.
1. Brake the vehicle with the parking brake and place wheel chocks under the wheels («shoes»),
2. If the work is not carried out on a viewing ditch or overpass, jack up all four wheels in turn and place the vehicle on supports. You can also do the job by successively lifting and removing the next wheel.
The sequence of fluid replacement in the brake mechanisms:
- right rear;
- left front;
- Left back;
- right front.
3. Turn away a stopper of a reservoir of the main brake cylinder.
4. Pump out the old brake fluid from the reservoir of the main brake cylinder with a medical syringe or a rubber bulb.
5. Add new brake fluid up to the lower edge of the filler neck.
6. Clean the protective caps of the air release valves of the brake mechanisms of the front and rear wheels from dirt...
7.... and remove the caps.
Note: Attach the hose to the right rear wheel brake slave cylinder bleed valve and immerse the end of the hose in a clean, transparent container.
8. The assistant should sharply press the brake pedal four to five times (with an interval between pressing 1-2 s), and then keep the pedal depressed.
9. Loosen the air release valve 1/2-3/4 turn. The old one will start to flow out of the hose (dirty) brake fluid. The brake pedal at this time should smoothly reach the stop. As soon as the fluid stops flowing, close the air release valve.
Note: Constantly monitor the liquid level in the tank, not allowing it to drop to the mark «MIN» on the wall of the tank. Top up with new brake fluid as needed to prevent air from entering the hydraulic drive. This ensures that the old liquid is gradually replaced by the new one without draining the hydraulic system.
10. In the same way, change the brake fluid in the working cylinder of the brake mechanism of the left front wheel by unscrewing the air release valve.
11. Repeat steps 6-9 until the fluid in the drive is completely replaced (clear fluid without air bubbles should flow from the hose).
12. Then change the brake fluid in the second circuit (first in the working cylinder of the brake mechanism of the left rear wheel, then the right front).
13. After changing the brake fluid, be sure to put on protective caps on the air release valves. Replace damaged caps.
14. Check the quality of the work done: press the brake pedal several times - the pedal stroke and the force on it should be the same each time you press it. If not, return to steps 6-10.
15. Add brake fluid to the mark «MAX» on the wall of the brake master cylinder reservoir. Close the tank with a lid.
16. After changing the brake fluid, be sure to put protective caps on the air release valves to prevent corrosion.