VW Rabbit brake servo. The brake servo (or booster) helps the master cylinder to create the required brake line pressure by using vacuum from the engine to apply extra pressure. If you need extra effort on the pedal to stop your Rabbit it is time to replace your brake booster servo. This remanufactured ATE brake booster measures 9.5" in diameter, and is not adjustable where the fork meets the brake pedal assembly. The studs for the master cylinder are 2.4" apart.
While installing this VW brake servo you will want to have new brake fluid ready. If you still have the original master cylinder installed on your Rabbit, consider purchasing a new one at the same time. You will the the master cylinder disconnected to complete the booster installation.