Vacuum Advance

[JC Mustang]

So, I discovered that my distributor's vacuum advance control is FUBARed (to put it nicely) and there isn't a second nipple to hook up another vacuum line to (although there is a hole where I think this nipple should be). Furthermore, it doesn't resemble too closely the replacement parts I'm seeing. What's the difference between the dual and single diaphragms? Is one of these correct/better for my application (1968 289)?

Also, it appears that a previous owner decided the vacuum control valve was unnecessary as there is a plug in the thermostat cover (where I believe the valve goes) and the single functional nipple on the vacuum advance was connected to the carburetor. Would there be any reason for such a setup?

Thanks!

 

[2+2GT]

Well, you can find whatever you want here:

Mustang Vacuum Diagrams, Shelby Vacuum Diagrams

The dingus screwed into the thermostat housing was the Distributor Vacuum Control Valve. It's purpose is to sense if the coolant temp rises to 220°. If it does, it exposes the retard from manifold vacuum to ambient air. This advances the timing at idle, speeding up the fan and water pump, which cools the engine.

I suspect you want this one: