Bleeding the brakes is required if the system has been opened in any place, or air has entered it in another way. Before bleeding the brakes, remove dirt and foreign bodies from the bleed valves and remove the reservoir cap.
If only one wheel cylinder or caliper has failed, it is usually sufficient to bleed only the corresponding circuit, i.e. the front left and rear right brake or the front right and rear left brake. Otherwise, bleeding can be started with both the front and rear brakes, but it is best to follow the sequence recommended by the manufacturer: rear left, front right, rear right and front left brakes. For pumping without assistance, there are many devices in car dealerships. When using one of these devices, you should be guided by the instructions for it. Otherwise, you need to resort to the help of an assistant.
1. After removing the boot, put a transparent hose on the appropriate bleed valve. Lower the other end of the hose into a bottle filled with some brake fluid.
2. Ask an assistant to press the brake pedal to the floor. Open the bleed valve half a turn with the pedal at the floor. Watch for brake fluid flowing out of the hose.
3. When air bubbles stop appearing in the liquid, the air has been removed. At the last roll, leave the pedal to the floor and close the bleed valve. Release the pedal slowly.
4. Do the same operation on the other bleed valves in the given sequence.
You should pay attention to the fact that it is necessary to monitor the level of brake fluid in the reservoir so that air cannot enter the system through the reservoir. Never fill the tank with liquid pumped out of the system. Do not use brake fluid that has been in an unsealed container for a long time.