VW power brake booster. The power brake servo is what provides the power assist in your Golf or Jetta. When it starts to go you will notice that much more effort is required to stop the car, or your brake pedal will go straight to the floor and barely stop the car. Servos can’t be repaired, so you will need to pick up this new high quality, direct fit replacement to make your Volkswagen stop safely again.
The VW power brake booster is not the only part of your brake system to cause your brake pedal to feel different than it did when your Golf or Jetta left the Volkswagen factory. One part would be the brake check valve, shown below, which holds the vacuum in the power brake booster, or it could be your master cylinder.