Distributor Advance Unit: Testing and Inspection

Mounted on the side of the upper body of the distributor housing is the vacuum advance control unit. This unit is connected to the stator base and when operating, rotates the breaker plate, causing the igniter to move. This advances or retards the ignition timing as required.

Vacuum Advance Test:

Inspection of the vacuum unit can be done with a hand operated vacuum pump, tachometer, and a timing light.

1. Connect timing light and tachometer. Disconnect the vacuum hose connected to the unit and connect a vacuum pump.

2. Connect the timing light to #1 spark plug wire and start the engine.

3. With the engine at idle, apply vacuum and measure the amount of ignition timing advance.


Malfunction Indicators:

Excessive Advance: Weak Vacuum Controller Spring.
Sudden Advance Rise: Broken Spring.
Insufficient Advance: Impaired Movement Of stator base.
No Advance: Broken Diaphragm.


Refer to COMPONENT REPLACEMENT AND REPAIR PROCEDURES for further information.