Reply to "Dual Diaphragm (vacuum advance/retard) Distributor"

Dave,

all US manufactured Clevelands were equipped with dual diaphragm dizzys throughout the 5 year production run from 1970 through 1974. This was part of the emissions controls employed in that era. Returning the vacuum/ignition system stock will not make your motor run better.

The diagram you posted is of a 1974 Pantera, which was equipped with EGR, something your car did not have. Your car would have been equipped with only one temperature controlled vacuum switch (TVS switch) for the distributor controls (called spark controls). The second TVS switch in the diagram is for the egr system, something your car doesn't have.

emissions wise, your '72 motor would have had 4 systems:

1. Positive crankcase ventillation
2. Evaporative emissions control (charcoal canister)
3. Heated air controls (air filter assembly)
4. Distributor controls (spark timing)

the single TVS switch in your car would be of the type with 3 nipples on it, and would have been screwed into the water pump, just as Jon has shown in the photograph.

Your '72 Cobra Jet also had a dual pont dizzy.

cowboy from hell