vacuum advance

[hcsstang]

I was at a local MCA show last Sun. and I was told that I should have the dual instead of a single advance. In the elbow I have a plug. What decides on which one that I should have . Every thing works with the single and I have no other holes for the vacuum lines. My car is a 302, automatic. Some one said that if you had smog devices the dual is used.

 

[GTCSMustang]

You were told wrong. It should be single advance for Mustangs with 302, 4-bbl, and automatic transmission.

Scott

 

[rvrtrash]

The plug in the thermostat housing is for a temp. switch that routes the vac. to your distributor. When water temp. increases, the switch changes the vac. source from your carb to the intake so the engine rpm will increase, driving the fan/water pump faster to help cool it off.

Steve

 

[robert campbell]

All
To my knowledge a Mustang built for California in 1968 should have the dual diaphragm distributor. This was part of the smog “stuff.” As Steve said it is in conjunction with a temperature activated switch in the thermo housing. The temperature switch worked with the distributor to alter advance curves at idle (vacuum) to curb emissions while at idle, in stop and go traffic as he engine came to op temperature. I like to call the distributor a “push me” “pull m” distributor when it has the dual diaphragm. Cars sold to DSO 72 should have them and cars sold outside of that DSO might not. In DSO 74 Seattle, this was not common. Denver cars were a special tune all of their own due to the altitude. I would doubt that your car should have a dual diaphragm.

Rob

 

[GTCSMustang]

The only small-block V-8 Mustang produced in 1968 without a dual-diaphram vacuum advance is a 302 4-bbl with automatic transmission. All other engine configurations had the dual-diaphram vacuum advance. California delivered 302 4-bbl Mustangs with automatic transmissions also had the single-diaphram vacuum advance. There should be one green striped hose coming from the vacuum advance to the center port on the thermal vacuum switch.