Bleeding the brakes is necessary to remove air from the hydraulic drive. Air can get into the hydraulic drive due to depressurization of the system during the repair or replacement of individual components, as well as when replacing the brake fluid. The presence of air in the brake actuator is indicated by an increased pedal travel and its «softness».
It is recommended to use a special machine for pumping hydraulic actuators under pressure in accordance with its operating instructions. If there is no installation, you can bleed the brake system by pressing the brake pedal. In this case, an assistant is needed. The efficiency of this method is lower, and labor costs are greater than when using a special installation.
When bleeding the brake system, keep an eye on the presence of fluid in the reservoir, avoiding exposing its bottom.
Before proceeding with pumping, eliminate the influence of the vacuum booster by pressing the brake pedal several times.
Remove air first from one circuit, then from the other, starting with the rear brake wheel cylinders.
Add brake fluid to the reservoir to the correct level.
Remove the protective caps from the air outlet fittings. Clean the fitting from dust and dirt.
Put a transparent tube on the head of the brake fitting of the right rear wheel, and lower its free end into a vessel partially filled with clean brake fluid. Depress the brake pedal to pressurize the hydraulic brake system. If no resistance is felt when pressing the pedal, press it slowly and without interruption until pressing requires any effort. Unscrew the fitting with the pedal pressed all the way down. After that, the assistant should slowly press the brake pedal and slowly release it, while the liquid, together with air, will be forced out of the system through the hose into the vessel. Repeat this process until bubbles stop coming out and clear fluid comes out of the hose, keep the pedal depressed and tighten the air outlet fitting tightly. Remove the hose and put the protective cap on the fitting.
Repeat operations for other wheels.
After pumping, restore the level of brake fluid in the reservoir if necessary. Do not use fluid drained from the system to fill the reservoir, as it is saturated with air, contains a lot of moisture and may be contaminated.