We bleed the brakes to remove air from the hydraulic drive after it has become depressurized when replacing the master cylinder, wheel brake cylinders, hoses, tubes, and also in the case of replacing the working fluid or when the brake pedal becomes "soft".
We remove air from the system with the engine not running, first from one circuit, and then from the other in the following sequence:
- brake mechanism of the right rear wheel;
- left front wheel brake mechanism;
- left rear wheel brake mechanism;
- brake mechanism of the right front wheel.
If air gets into one of the circuits, it is enough to bleed only this circuit, and not the entire hydraulic drive. Before bleeding, check the level of the working fluid in the brake system hydraulic drive reservoir and add fluid if necessary (see "Checking the fluid level in the brake hydraulic reservoir"). We bleed the brakes with an assistant. If the rear wheels are off the ground...
...we insert a screwdriver between the piston of the pressure regulator in the hydraulic drive of the rear wheel brake mechanisms and the piston lever, fixing the piston of the regulator in the recessed position.
We clean the dirt from the brake bleed nipple of the right rear wheel.
...and remove the protective cap from it.
Using an 8 mm open-end wrench, loosen the bleed nipple. We put a hose on the fitting and immerse its free end in a container partially filled with working fluid.
The assistant should vigorously press the brake pedal all the way down 4-5 times and hold it pressed.
Using an 8 mm spanner, loosen the bleed nipple by 1/2–3/4 of a turn.
In this case, liquid with air bubbles will flow out of the hose, and the brake pedal should be pressed all the way down.
As soon as the liquid stops flowing out of the hose, tighten the nipple and only after that can the assistant release the pedal. We repeat the pumping until air bubbles stop appearing in the liquid coming out of the hose. We remove the hose, wipe the bleed nipple dry and put a protective cap on it. We bleed the brake mechanism of the left front wheel.
For this...
...remove the protective cap from the lower bleed nipple of the left front wheel working cylinder block.
We put a hose on the fitting and lower its free end into a container partially filled with brake fluid.
We remove air through the lower nipple of the working cylinder block.
In the same way, we remove air through the upper nipple of the left front wheel working cylinder block (shown in the photo by an arrow). We bleed the brake mechanisms of the other circuit in the same way.
When pumping, you need to monitor the fluid level in the tank and add fluid if necessary.
If you feel the brake pedal is "soft" and has an increased travel when you press it, this means there is air left in the system. In this case, we repeat the pumping until the pedal becomes "hard", that is, when pressed, it does not travel more than half the distance to the floor. If the air cannot be removed, check the tightness of the connections, pipelines, hoses, master and working cylinders. We tighten leaking connections, replace faulty master and slave cylinders (see "Brake system"). We replace the working fluid in the hydraulic drive of the brake system in accordance with the maintenance regulations - every three years.
When replacing, pump out the old fluid from the tank using a syringe or rubber bulb.
We pour new liquid into the tank. We bleed the hydraulic drive of the brake system until the new fluid (lighter than the old one) will not start to come out of the bleeding nipples of all working cylinders. After bleeding the brakes, bring the fluid level in the brake system hydraulic drive reservoir to the norm (see "Checking the fluid level in the brake hydraulic reservoir").