It is the ability of the Volkswagen brake master cylinder to generate pressure in the hydraulic system that provides a means for your vehicle to stop. The components in this hydraulic pressure building component are all metal except for the polymer seals on the piston. It is these seals that rupture in time; making it possible for the hydraulic fluid to slip past the piston preventing the ability of this braking device from building pressure in the system. The brake master cylinder has a prominent place under the hood of your Volkswagen. By looking on the fire wall on the driver side of the vehicle the brake master cylinder can be found mounted to the brake booster assembly. With the lid removed, the piston in the bottom of the Volkswagen brake master cylinder can be seen. When the brake pedal is being depressed, a fountain of fluid should be able to be seen rising up out of the reservoir in this braking component. When a ruptured seal on the piston is present, this fountain is diminished in size. The driver of the Volkswagen will experience a noticeable reduction in the resistance the brake pedal has when it is being depressed. This is present because of the piston's inability to hold the hydraulic fluid on one side of the piston because of the ruptured seals. Because of this pressure cannot be transported to the brake pads and shoes to assist in stopping your vehicle. A faulty brake master cylinder is the only hydraulic braking component on your Volkswagen that will not have an external leak when it is failing. That is why the driver must be aware of the symptoms involving a faulty brake master cylinder in the way the brake pedal feels to help prevent total brake system failure.