1970 Cadillac Coupe vacuum solenoid connecter

[Bill Balkie 24172]

Hello , I am wondering if someone can answer a question I have. I have a vacuum solenoid between my coil and distributor it has three vacuum lines hooked up to it and a two prong electric connection. On the female part of the connection it has what looks like some type of electric diode connecting the two wires on the female connecter . Have you ever noticed this on any of your cars ? Is this something that somebody rigged up in the past ? Just doesn't  look right to me . It is spliced into the connection very professionally . What is your opinion ?  Stock or some type of modification . I have added a picture .
     Bill

[Cape Cod Fleetwood]

Do you have an electrical connection going to your compressor?
I have no idea what that is, nothing like that on my car. Looks like a resistor for something.

[TJ Hopland]

Wasn't 70 one of the years that had the spark retard thing that kicked in either at a speed or in high gear?  I thought Cad usually had a speed sensor but I know other GM's used a switch in the transmission.

[Bill Balkie 24172]

Hello Laurie , of course I have an electrical connector to my compressor. My air conditioner works fine. This is a solenoid between the distributor and the  coil it has three vacuum lines going to it and one electrical connector very similar to the connector on the air conditioner compressor. However the connector on the vacuum solenoid has a electrical diode of some type.

[Kurt Weess]

The components you describe are part of the Transmission Controlled Spark Advance System designed to reduce exhaust emissions.  It shuts off the vacuum to the distributor vacuum advance during 1st and 2nd gear.  The electrical signal comes from a pressure switch inside the transmission that is closed in 3rd and reverse gear.  The components you show in your pictures are identical to what I have on my 70 Fleetwood right down to the resistor between the contacts.  My suggestion would be to remove and disconnect the solenoid and run manifold vacuum to the distributor vacuum advance.  You car will run much better on full manifold vacuum vs this system.  I've attached page 6-42 from the service manual that shows this system.  Full description can be found on page 6-43.

[Bill Balkie 24172]

Kurt ,
    Thank you so much for your response. I was not sure if this was some homemade rig by previous owner. The way the resistor was crimped to the terminals look like it was factory. I will certainly try your suggestion as soon as I can. I am not quite sure what to do with the other vacuum lines since I will be removing the solenoid. I have sent you a PM

      Bill

[klinebau]

You can remove the line from the rear of the carburetor.  This is not under vacuum and is only used to provide filtered air.  You should plug the fitting on the rear of the carburetor to prevent unfiltered air getting in the engine, but it won't affect the running vehicle if not covered.  Run a new vacuum line from the ported manifold port on the carburetor to the "C' port on the thermal vacuum switch.

This will give you "ported vacuum" to the distributor.  I won't go into the ported versus manifold vacuum argument here, but I believe this is the best configuration.  You can look up that argument on this forum and others.

[Cape Cod Fleetwood]

Hello Laurie , of course I have an electrical connector to my compressor. My air conditioner works fine.

I didn't mean to insult you, my apologies.

[Bill Balkie 24172]

Hello Laurie,
     You could never insult me .  I just sometimes reach a point of frustration .  I love reading your stories and adventures with your car . You have been around the block more then a few times with your Fleetwood and I respect the love you have for the car .  You are a nice terrific asset to this forum. And I really like the love you give to our old friend Charles.

      Bill

[Bill Balkie 24172]

Hello ,
   I really appreciate the suggestions on bypassing the vacuum solenoid. The question that I was really concerned with was this set  up stock from the factory  . Apparently it is stock from the factory but maybe not installed on all cars.   It seems like my vacuum solenoid is working fine. I have no real issues with the car. But it is interesting the recommendations from Klinebau and Kurt . As long as the system Seems to be working would it still be wise to convert it over and bypass the vacuum solenoid.  Kurt made a point that the car would run better .  Now i am up in the air about removing the Vacuum solenoid. There is nothing wrong with having the car run better . Why did G M set it up that way in the first place .  I think if that solenoid should go bad and the part can not be found the alternative would be the way to go. I like to keep things simple removing the vacuum solenoid would definitely make it simpler.

    Bill

     

[klinebau]

This is an emissions strategy intended to reduce nitric oxide (NOx).  For 1970, instead of using EGR and AIR systems, they came up with the transmission controlled spark (TCS) strategy.  The TCS solenoid will disable vacuum advance on the distributor until the transmission is in third gear.  A leaner mixture will produce more NOx and retarding spark timing will reduce this emission.

A lot of 472/500 owners like to use the pulley arrangement from 1970 as it eliminates the air pump and extra belt used in later engines.  In theory, the engine will be a little more efficient in first and second gear under part throttle with the elimination of the TCS, but how much time does the engine really spend there?  You probably aren't going to see much difference if yours is hooked up correctly and working.  Many vehicles are missing this part (like mine) as they were discarded during service.

[Bill Balkie 24172]

Hello Klinebau ,
     Thank you for all your help and research . I am going to save your post and keep it with my notes .

    Bill