Bleeding the brake hydraulic system (VW Passat B4)

Bleeding of the brake hydraulic drive should be performed in all cases when during the performance of any work the hydraulic drive becomes leaky. The brake hydraulic drive should also be bled when the brake pedal becomes "soft" or when several presses of the brake pedal are required for effective braking.

Warning

1. It is prohibited to unscrew the nipples for bleeding the hydraulic circuit of the rear wheel brakes when the brake pedal is pressed or the pressure accumulator is charged.

2. The pressure of the charged pressure accumulator of the rear wheel circuit is 180 kgf/cm². Therefore, before performing any work on the brake system, discharge the pressure accumulator by pressing the brake pedal at least 20 times.

3. When bleeding the hydraulic drive, it is prohibited to turn on the ignition, except in specially indicated cases.

4. To fill and restore the brake fluid level, use only fresh fluid of the specified brand.

5. When bleeding, constantly restore the normal fluid level in the tank.

Bleeding of the front wheel circuit is performed on both front wheels, for which remove the protective caps from the air release nipples. Clean the nipples from dust and dirt.

Place a transparent tube on the head of the brake nipple of the right wheel, and lower its free end into a container filled ⅓ with clean brake fluid. Press the brake pedal to create pressure in the brake gas system. If you do not feel resistance when you press the pedal, slowly and continuously press it until pressing it does not require any effort. Unscrew the nipple by ½ a turn with the pedal pressed all the way. After this, the assistant should slowly press the brake pedal and slowly release it, while the liquid together with the air will be forced out of the system through the hose into the container. Repeat this process until bubbles stop coming out and clean liquid starts coming out of the hose, hold the pedal in the pressed position and tightly screw the nipple to release air. Remove the hose and put a protective cap on the nipple.



Repeat the operations for the left wheel.

After bleeding, restore the brake fluid level 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. Bleeding of the rear wheel circuit is performed on both rear wheels, for which remove the protective cap from the bleed nipple, put a transparent tube on its head and lower the free end of the tube into a container filled with brake fluid. Press the brake pedal, with the pedal pressed, unscrew the bleed nipple and turn on the ignition, which will cause the ABS pump to turn on. Wait until the air bubbles with the liquid stop coming out, then release the brake pedal and screw in the bleed nipple.

Turn off the ignition and wait until the ABS pump stops before bleeding the other rear wheel circuit.