1969 Deville Convertible 472 vacuum lines on the distributor.

[David P. Barter]

Hello Folks,

I have a question regarding the vacuum pull offs on the distributor. I know one goes to the pot beside it. the middle one goes to the carburetor pull off and on my car someone took the third line, pulled it off what ever it connected to and plugged it. Can someone tell me what it goes to? I cannot find it in my service manual.

[The Tassie Devil(le)]

I thought that there was only one vacuum port on the Distributor.

Bruce.

[David P. Barter]

HI Bruce.

That very well maybe, but there is small three port block right beside the distributor that I cannot trace where that last line goes. Someone pulled it off where ever it terminated and plugged with a screw...

[The Tassie Devil(le)]

So you are looking at the heat-related vacuum switch that is in the block that operates the vacuum advance to the distributor when the coolant water is hot enough to open the internal port?

In this case, I cannot assist you, as I always convert any engine with this feature to full Manifold Vacuum to the Distributor for improved driveability.

The Workshop Manual should show it under Emission Controls System, and there should be a 12 Volt Speed Control Switch Vacuum Line to the centre port.

The port closest to the Block is the Manifold Vacuum port to the carby, the next is the Speed Control, and the outer one, to the Distributor.

This way, the Distributor can only receive Vacuum when the engine is warm enough, and the electrically operated Speed Control only supplies Ported Vacuum until that time.

Bruce.

[David P. Barter]

Thanks Bruce that is exactly what i was looking at. it seems that third line off the switch is supposed to go to the firewall and then in the passenger compartment to supply vacuum to the AC solution. According to this post on another site.

http://www.cadillacforums.com/forums/500-472-425-368/96263-1969-deville-thermal-vacuum-switch.html

However I like your idea and will make the change tomorrow! Thanks again for the quick response!

[The Tassie Devil(le)]

G'day David,

When you source the full manifold vacuum, go to the junction in the Intake Manifold where the Transmission Modulator line is attached, and put a "T" junction to accept the distributor hose.

Then time the distributor advance with the vacuum off and plugged, to around 8 degrees advance.  When you reattach the hose, the timing light indication will immediately jume to around 24 degrees.   This is normal.

Plus, block off the non-used ports in the carby with plugs that are available at most spare parts shops.   If you can't find any, simply get a piece of hose, and a slightly oversize ball bearing, and insert the ball in the end of the hose, to act as a plug.

Bruce.

[Glen]

The attached pages of the 69 Shop Manual should help you.     

[Scot Minesinger]

This vacuum diagram is in the Engine section of shop manual (#6 I think), under electrical.  Leaf through it by the timing section you will see this three ported vacuum switch and how it is piped.  The vacuum diagram for the car is all there in the shop manual, you just have to piece it together from the various sections.  Best to look at an unmolested original at a show, or there may be a comprehensive diagram published by Cadillac.  I got one for my 1970.  The purpose of this is to speed idle when car gets hot using manifold vacuum instead of ported vacuum to advance timing.  Common port is to distributor, the other two are ported vacuum (from the below 220'F side) and manifold vacuum from (above 220'F switched port).