on the original 400's, there was a couple vacuum switches mounted into the thermostat housing. I think one of them was for the vacuum advance to the distributor - is this correct? And if so, is it necessary to use this thermal vacuum switch for the distributor vacuum advance or can the vacuum advance be tied directly into the carb base?

 

There are myriad different types of these valves.

One each one is a raised ovate section, has an ID engineering prefix/suffix marked on it, post what they are.

Similar to this: D7AE-A1A

 

Not a 400 guy, but the ones linked to distributor vacuum I've ran across, kept vacuum advance from working till engine reached a certain temp.

 

I had one out of the T stat housing yesterday, threads were bad so I took it to an autoparts store to find a tap and the switchs are still available , fyi

 

Bill - Numberdummy (or others): i found the vacuum switches finally lol One is a Brown color with ID D7AE-B1A and the other one is yellow color marked D7AE-A1A. Both are 3 port switches. My question is: do I need either of these for the vacuum advance on a Duraspark II distributor or will the distributor not really care if I have a vacuum switch installed in the vacuum advance line that goes from the carburetor to the distributor? If I need one of them, which one and how do i connect the vacuum lines? I see there is a port marked with a - symbol.

 

The color is indicative of the activation temperature of the switch.

 

The three-port switch is for the vacuum advance; it switches out manifold vacuum vs. ported vacuum to the vacuum advance based on temperature. In my experience, you can safely forgo this switch and connect the advance directly to the spark port (passenger side on the base). Obviously it would be better to stick with the factory configuration, but from what I have seen, you can get by without it assuming your initial timing is set high enough.

A two-port switch is typically used to cut off the vacuum source to the EGR valve under a certain temperature, and if you have an EGR system then you do need this switch - and if you originally had an EGR system then you do need an EGR system.

 

Although you can hook the vacuum advance up directly to ported vacuum at the carburetor without any problems, the vacuum switch on the thermostat housing does serve a useful function.

The switch on mine is red, and it has 3 marked ports - 1, D, and 2. Port "D" is where the distributor connects to. Port "1" connects to ported vacuum at the carburetor, and Port "2" connects to manifold vacuum at the vacuum tree on the back of the intake manifold.

This switch is rated for 225 degrees, meaning the engine uses Port "1" (ported vacuum) under normal conditions. However, if the engine begins to approach 225 degrees, this switch will cut off Port "1" and turn on Port "2" to give the engine full manifold advance. What this does is speed the engine idle up, which in turn speeds up the water pump, which helps to cool your engine off faster. Once the engine is cooler than 225 degrees, the switch returns to the normal Port "1" again.

 

lariat85 - thanks for that detailed explanation, I'll keep this for reference for sure. For right now I've put in plugs into the thermostat housing where these vacuum switches go. If I have troubles with timing when engine is cold vs. hot, I'll put in the red switch I have and follow your directions.
Thanks again!