Bronco L6-300 4.9L VIN Y 1-bbl (1983)
Distributor Advance Unit: Description and Operation
Vacuum Spark Advance Mechanism
The vacuum spark control mechanism can provide spark advance if a single diaphragm assembly is used or spark advance and retard if a dual
diaphragm assembly is used. The diaphragm assembly used depends on the engine calibration.
Single Diaphragm Assembly
SINGLE DIAPHRAGM ASSEMBLY
The single diaphragm assembly, Fig. 11, also changes the armature to stator relationship to give spark advance. The stator assembly position is changed
by means of vacuum being applied to the diaphragm assembly. Vacuum applied to the diaphragm assembly causes the diaphragm and attached
diaphragm rod to move, compressing the advance spring, which controls the rate of advance. The movement of the diaphragm rod, which is attached to
the stator assembly, makes the the stator assembly move with respect to the armature. This changes the initial armature to stator relationship set during
initial timing, causing spark advance. The stator assembly is mounted on the lower plate assembly which with the diaphragm assembly, is attached to the
distributor base.
