Brake system components (VW Passat B6)

Pressure regulator

The pressure regulator limits the output pressure to the rear brakes after the pressure has reached the maximum value in the master cylinder. The regulator is used when less force is required to be applied to the rear brakes to achieve optimum braking.

Brake fluid level sensor

The brake fluid level sensor, located in the brake fluid reservoir, turns on the BRAKE indicator lamp when it detects a low brake fluid level. Once the brake fluid level reaches the required level, BRAKE goes out.

Vacuum brake booster

The vacuum brake booster reduces the force on the brake pedal, making it easier to drive. The vacuum amplifier uses a diaphragm, which has a vacuum on both sides during normal operation. When braking, air is supplied from one side of the diaphragm, thereby creating atmospheric pressure. Due to the pressure difference transmitted through the diaphragm, the pusher moves in the direction of vacuum (vacuum), providing an auxiliary force for braking. When the brake pedal is released, air is pumped out of the booster cavity through the control valve and a vacuum is created.

Master brake cylinder

The brake master cylinder is designed for use on dual circuit brake systems. The front brake mechanism and the rear left brake mechanism are actuated by a primary piston, and the front left brake mechanism and the rear right brake mechanism are actuated by a secondary piston. The brake master cylinder combines the functions of a standard dual brake master cylinder, as well as a low brake fluid level indicator and a brake pressure regulator.

Caution: Replace all parts included in the repair kit used to service the brake master cylinder.

Caution: When installing, lubricate the rubber parts with clean brake fluid to facilitate assembly. Do not use industrial compressed air to dry and clean the brake mechanism parts. This may damage the rubber parts. If any part of the hydraulic system is removed or disconnected, bleed the brake system completely.

Note: Tightening torque values are set for dry, unlubricated fastening.

Caution: Perform all repair work on a clean workbench free of mineral oil stains.

Disc brakes on the front wheels

The brake caliper is attached to the steering knuckle with two bolts. The fluid pressure created by pressing the brake pedal is converted into braking force. This force acts equally on the piston and the caliper. As a result, the piston moves outward and the caliper moves inward, squeezing the brake disc. When compressed, a friction force is created between the friction linings of the brake pads and the brake discs, which helps stop the car.

Caution: Always replace all pads on one axle of the vehicle, even if only one pad is worn. If brake pads are reinstalled, they must be marked before removal.

When the brake pedal is pressed, the brake fluid presses on the piston, moving it out of the cylinder. The piston seal moves along with the cylinder when significant pressure is applied to the piston. However, since part of the piston seal is fixed in a groove whose shape corresponds to the shape of the seal, the upper part of the seal is deformed in the direction of piston movement.


When the brake pedal is released, the brake fluid pressure decreases and the elastic force created by the deformation of the piston seal returns the piston to its original position.

As the brake pads wear and the gap between the brake disc and the pads increases, the piston moves even further, thereby maintaining the gap. The seal may change shape later, but since the inner part of the seal is fixed in the groove of the cylinder, the amount of deformation remains the same. The piston moves further to cover the gap distance. Since the piston returns the same distance, and the rubber seal returns the piston to its original position, the gap between the brake disc and the brake pads is maintained at the required level.