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Old Apr 6, 2007 | 07:07 AM
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what is it for

on the front of my 351M motor i have a 3 prong vacuum tree about 2.5 inches tall i was told it had something to do with heat regulating. does anyone know what it is and where the lines would go? there are no vacuum lines attached to it and i can't seem to find it on a schematic. the motor is in a 78 f-150 4x4.
 
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Old Apr 6, 2007 | 07:51 AM
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I assume you're referring to the one on top of the thermostat housing.

Mine wasn't hooked up either. After disassembly, it appeared to be a temperature sensitive switch...i.e. as the coolant warmed up, the vacuum was redirected. I imagine the temerature controlled vacuum would have gone to the choke.

However, as I said, mine wasn't hooked up, and the switch wasn't healthy, so I just pulled it out all together and used that port for a mechanical water temp gauge.
 
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Old Apr 6, 2007 | 08:03 AM
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D7AZ-12A091-A .. Distributor Vacuum Control Valve~fits 1977/79 E & F100/350 351M/400 and dozens of other applications.

It's part of the smog system, that's prolly why it isn't hooked up. These have been on most Ford cars and trucks since 1968 (there are others besides the one I listed, some have 4 ports). Many have been removed, or have had the vacuum lines disconnected.
 

Last edited by NumberDummy; Apr 6, 2007 at 08:10 AM.
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Old Apr 6, 2007 | 09:50 AM
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You may want to look at these,

https://www.ford-trucks.com/user_gal...136672&width=0

http://www.clubfte.com/users/mil1ion...mDiagrams.html


Wally Womack
 

Last edited by Pro-Street/StateTK; Apr 6, 2007 at 10:01 AM.
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Old Apr 6, 2007 | 02:21 PM
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It is a thermal vacuum switch to block cold vacuum and allow
warm vacuum flow. VCV

This should explain it visually.

 
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Old Apr 6, 2007 | 02:29 PM
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Originally Posted by tcbofade
it appeared to be a temperature sensitive switch...i.e. as the coolant warmed up, the vacuum was redirected. I imagine the temerature controlled vacuum ...
YAY!! I got one right, kind of...

Those diagrams are clear as mud to me.

Dennis, could you label the switch in question on that diagram? Pretty please?
 
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Old Apr 6, 2007 | 02:35 PM
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Directly right of the word FRONT.

This gives me an idea for a part identification album
 

Last edited by Mil1ion; Apr 6, 2007 at 02:38 PM.
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Old Apr 6, 2007 | 02:38 PM
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Thank you.

As you know, I'm about to begin a rebuild on a 400 then do an engine swap.

Seems to me that I read somewhere that I can leave most of these vacuum lines out of the plan.

I need to have a vacuum line for the distributor, one for the transmission modulator, and one for the choke....that I know of...is any of the rest of this really needed?

(Sorry for the hijack...)
 
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Old Apr 6, 2007 | 02:39 PM
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The one for the choke comes out of the intake directly below

The A/T
The Vacuum advance
A/C (if req'd)
1/2" line for Brake Booster.(if req'd)
 
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Old Apr 6, 2007 | 02:40 PM
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Originally Posted by Mil1ion
This gives me an idea for a part identification album
Sounds like a GREAT idea to me...and you are the guy to do it!!!
 
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Old Apr 6, 2007 | 02:41 PM
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Originally Posted by Mil1ion
1/2" line for Brake Booster.(if req'd)
Oh yeah...

Brakes? Who needs brakes?
 
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Old Apr 6, 2007 | 02:46 PM
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I am pretty sure they are used to switch the vacuum supply at the Dist from ported to manifold to speed up RPM if the engine starts to overheat at idle. That is how mine is hooked up and it works fine.
 
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Old Apr 6, 2007 | 06:54 PM
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Originally Posted by Mil1ion
Directly right of the word FRONT.

This gives me an idea for a part identification album
That'd be really great.

I'm still figuring this stupid vacuum schematic on my 400. I need a walk through.
 
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Old Apr 6, 2007 | 09:00 PM
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Just print out the picture and trace thru it.
 
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Old Apr 6, 2007 | 09:09 PM
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Jerm, have you not seen the illustrations of vacuum hose routing in my album ?
 
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