Pressure Testing Regulator or Proportioning Valves

Testing the pressure-regulating function of either system requires measuring brake system pressure at each wheel, using two pressure gauges with a range of at least 160 bar (2320 psi) connected in place of the brake bleeder valves. Because of the need for this specialized equipment, we recommend having this test performed by an authorized Volkswagen dealer or other qualified repair shop.

The gauges are connected to one front and the diagonally opposite rear brake to test one hydraulic circuit, and then to the other front brake and its diagonally opposite rear brake to test the other hydraulic circuit. The system must be bled at the gauges each time they are connected. Have a helper depress the brake pedal while observing the pressure readings on the gauges. The fuel tank should be full and the suspension must be in its normal resting position, either on the ground or held with spring tensioners.

Table c lists the brake pressure specifications for different conditions and models. Load-sensing pressure regulators can be adjusted by moving the bolt which attaches the spring to the rear axle bracket, to increase or decrease tension on the spring. Replace the regulator if it cannot be adjusted to operate within specifications.

Table c. Brake Pressure Specifications