Lesson3/Learning Event 1
FIGURE 26. VACUUM TIMING CONTROLS.
Vacuum advance mechanisms are not used on tactical wheeled vehicles, but they are commonly
used on civilian-type vehicles and on Army staff cars. This type of advance uses a vacuum
chamber which is connected to the intake manifold and a vacuum diaphragm which is linked to
the distributor plate. There is a diaphragm spring on the vacuum side of the diaphragm.
When the engine is not running, air pressure on both sides of the diaphragm is equal. The spring
pushes the breaker plate to the retarded position.