In this case, it is necessary to remove this air from the brake system. The presence of air in the pipelines can also be judged by the fact that when you press the brake pedal, no strong resistance is felt.
In this case, it is necessary to eliminate the leakage and remove air from the system.
In workshops, bleeding from the system is carried out using a combined device for filling brake fluid and bleeding the brake system.
Attention! When using the mentioned device, the pressure in the system should not exceed 1 bar.
You can do without tools. In this case, the air from the brake system is removed by pumping with the brake pedal. An assistant is needed for this operation.
If you need to bleed the entire system, then you need to remove air from each wheel cylinder.
If the caliper of only one brake mechanism was replaced or repaired, then, as a rule, it is enough just to remove air from the corresponding wheel cylinder.
Vehicles with ABS
Attention! If one of the chambers of the brake fluid expansion tank has been completely emptied, for example, due to leakage or carelessness when bleeding the brake system, then air also enters the ABS hydraulic booster pump. In this case, bleeding the brake system should be carried out in a workshop using a special device.
Air removal sequence:
- A) brake mechanism of the rear right wheel;
- b) rear left wheel brake;
- V) brake mechanism of the front right wheel;
- G) front left wheel brake.
Attention! Loosen the bleeder fittings carefully so as not to strip the threads. It is recommended to apply a rust converter to the fitting threads two hours before bleeding the system or caliper. If the fitting, despite the measures taken, does not open, it is recommended to contact the workshop and perform pumping there.
Attention! During pumping from time to time check the level of brake fluid in the expansion tank. The level of the brake fluid in the reservoir must not be allowed to drop to the limit or at all, so that the reservoir is «devastated». In this case, air will be pumped into the system. Replenish the amount of brake fluid in the expansion tank, adding only fresh fluid!
In vehicles with a brake force regulator, when bleeding the rear wheel brake system, move the regulator lever.
1. Remove a protective cap from the union of prorolling of the working brake cylinder. Clean the fitting, put a clean hose on it, lower the other end of the hose into a container half filled with brake fluid (see illustration). To unscrew the fittings, use a wrench designed for unscrewing the bleed fittings, for example, HAZET 1968-N.
Attention! Keep collected liquid out of reach of children.
2. Ask an assistant to depress the brake pedal to the end («sway»), until pressure builds up in the brake system. It is felt by the increase in resistance when the pedal is depressed.
After the appearance of sufficient = pressure, the pedal should be squeezed out to the stop and held in this position.
3. Loosen the bleed valve with a spanner about half a turn. Collect escaping brake fluid in a container. Make sure that the end of the hose in the container for collecting the escaping brake fluid is constantly below the fluid level.
4. Close the bleeder plug as soon as the brake fluid pressure in the fluid system decreases.
5. Repeat pressurizing the brake system with the brake pedal. Then press the brake pedal down to the stop and hold it with your foot. Open the bleeder valve and, as soon as the pressure in the system drops as the brake fluid flows out, close the bleeder valve.
6. Repeat pumping the system on one wheel cylinder until no air bubbles appear in the liquid flowing into the container.
7. Tighten the bleeder with a washer to a torque of KG Nm, the bleeder without a washer to a torque of 7 Nm.
8. After removing air, remove the hose from the bleeder union and close the union with a dust cap.
In the same way, remove the air from the remaining wheel cylinders, while observing the bleeding sequence.
9. Fill the expansion tank with brake fluid up to the maximum mark and screw the cap onto the filler neck.
Attention! Make sure that:
- A) brake hoses are securely connected;
- b) the brake hose is fixed in the holder;
- V) fittings for bleeding the brake actuator are wrapped;
- G) there is enough brake fluid in the expansion tank.
10. Carry out a leak test of the brake system with the engine running. To do this, depress the brake pedal with a force of 200-300 N (20 -30 kg) for approximately 10 seconds. The pressure in the system and, accordingly, the resistance of the brake pedal, should not decrease. Check all connections for tightness.
11. Apply a few brakes on a light road. At least one braking operation must be performed so that the ABS is activated, which is felt by the pulsation of the brake pedal.
Attention! When checking the brake system in this way, take into account the situation on the road and keep an eye on the traffic behind you.
Attention! Brake fluid must be disposed of at designated collection points.