Section 2 (Ignition System - BOSCH Single Breaker (Federal)): Description
WARNING: This page is about a different car, the 1983 Volkswagen Vanagon. However, it is still accessible from the selected car via links, so may be relevant.
Vanagon Federal models are equipped with a conventional, single breaker distributor, with centrifugal advance and vacuum advance and/or retard unit.
Vacuum units may be single or dual diaphragm, and are linked to the movable portion of the breaker plate assembly to advance or retard spark.
NOTE:
Some distributors may use a dual diaphragm unit to provide retard only (vacuum advance side not used).