SAAC Forum

The Cars => 1968 Shelby GT350/500/500KR => Topic started by: shelbydoug on June 29, 2020, 09:27:04 AM

Title: Thermostatc vacuum switch
Post by: shelbydoug on June 29, 2020, 09:27:04 AM
The vacuum tower on top of the thermostat housing.

What is it supposed to do? How do I test it to see if it's working?

On a manual shift car, it's my understanding that 1) when cold it is completely closed 2) the engine vacuum goes to the bottom port 3) vacuum advance to the middle port 4) top port to timed vacuum on the carb?

Is it supposed to re-route vacuum depending on engine temp?
Title: Re: Thermostatc vacuum switch
Post by: Krelboyne on June 29, 2020, 10:42:08 AM
I Believe that it blocks vacuum until operating temperature is reached.
Title: Re: Thermostatc vacuum switch
Post by: shelbydoug on June 29, 2020, 03:28:19 PM
I presumed that but I have one on the bench and am trying to make it work there. So far, no good.

I've never seen engineering data specifically stating that it opens at a specific temperature.

Operating temperature could vary depending on thermostats.
Title: Re: Thermostatc vacuum switch
Post by: CharlesTurner on June 29, 2020, 04:11:28 PM
Checked the Ford shop manual?
Title: Re: Thermostatc vacuum switch
Post by: J_Speegle on June 29, 2020, 04:29:26 PM
In Ford training and in state/national emission training manuals didn't find anything that specified an exact temperature range. Can offer the following description as to how it works (in some applications the lower port is just a filter)

(http://www.concoursmustang.com/forum/gallery/14/6-290620162533.jpeg)


And Ford's testing process for service personal from the period

(http://www.concoursmustang.com/forum/gallery/14/6-290620162602.jpeg)

Hope this helps
Title: Re: Thermostatc vacuum switch
Post by: shelbydoug on June 29, 2020, 05:08:36 PM
Checked the Ford shop manual?

What I see in the Shop manual is just the vacuum hose diagram. I see no reference to what temp it opens or begins to open at.

I am presuming that the Ford reference "to carburetor" means to the timed vacuum port and  not to manifold vacuum at the carburetor?

Perhaps termanology has changed since then but this is a little oonfusing.

Again, there is no mention of NORMAL operating temperatures? Considering the location being on the radiator side of the thermostat housing I think it will open as the thermostat opens but if it is set to work with a 192 thermostat, how will it work with a 160?
Title: Re: Thermostatc vacuum switch
Post by: J_Speegle on June 29, 2020, 05:36:54 PM
I am presuming that the Ford reference "to carburetor" means to the timed vacuum port and  not to manifold vacuum at the carburetor?

The diagram Ford showed in the description identifies (both manifold and carburetor) the port connections based on the application they choose for this publication. Connections for other applications would differ.  The full engine vacuum diagrams would answer that question for your given application.

Title: Re: Thermostatc vacuum switch
Post by: shelbydoug on June 29, 2020, 06:53:07 PM
I have them but they DON'T differentiate on "carburetor vacuum.

However, thank you for attempting to help here. I do appreciate it. ;)
Title: Re: Thermostatc vacuum switch
Post by: Krelboyne on June 29, 2020, 11:54:30 PM
The test is watching idle speed to increase and for the temperature light to get lit.  :o
Title: Re: Thermostatc vacuum switch
Post by: shelbydoug on June 30, 2020, 08:57:13 AM
That would be one way but now have two of them and can't make either open using a heat gun on the workbench.

I'll eventually get to the bottom of this. I was just trying to take a faster route to the solution and answers.

I should also point out that the shop manual shows four different hose routings depending on on BB, SB, auto or manual trans. On the surface the differences make no sense since there is contradiction in function under different routing.

I don't doubt their acuracy. I doubt my ability to understand the application of English language terms.

I often cut the technicians some slack and leeway in their attempts to explain technical details. It often strikes me as Einstein trying to write Shakespear. Both geniuses of their own just needing another genius to interpret WTF they just said and that ain't me?  ::)
Title: Re: Thermostatc vacuum switch
Post by: Bob Gaines on June 30, 2020, 10:36:39 AM
That would be one way but now have two of them and can't make either open using a heat gun on the workbench.

I'll eventually get to the bottom of this. I was just trying to take a faster route to the solution and answers.

I should also point out that the shop manual shows four different hose routings depending on on BB, SB, auto or manual trans. On the surface the differences make no sense since there is contradiction in function under different routing.

I don't doubt their acuracy. I doubt my ability to understand the application of English language terms.

I often cut the technicians some slack and leeway in their attempts to explain technical details. It often strikes me as Einstein trying to write Shakespear. Both geniuses of their own just needing another genius to interpret WTF they just said and that ain't me?  ::)
Have you tried suspending the vacuum switch in a pot of water on a stove top? Have your vacuum lines attached out of the water to check air flow from. The water temp can more easily be  monitored compared to a heat gun. Just a thought .
Title: Re: Thermostatc vacuum switch
Post by: Royce Peterson on June 30, 2020, 12:08:12 PM
Yes this is the right way to test both the vacuum valves and thermostats. It also is a great way to test temp sender units.

Bear in mind Ford had to meet federal emission standards in '67 and '68 depending on where the car was going to be sold. So the installation hook up does vary by application. You may find that it performs better in one of the other methods of hookup now that the car doesn't need to meet any specific specs.

That would be one way but now have two of them and can't make either open using a heat gun on the workbench.

I'll eventually get to the bottom of this. I was just trying to take a faster route to the solution and answers.

I should also point out that the shop manual shows four different hose routings depending on on BB, SB, auto or manual trans. On the surface the differences make no sense since there is contradiction in function under different routing.

I don't doubt their acuracy. I doubt my ability to understand the application of English language terms.

I often cut the technicians some slack and leeway in their attempts to explain technical details. It often strikes me as Einstein trying to write Shakespear. Both geniuses of their own just needing another genius to interpret WTF they just said and that ain't me?  ::)
Have you tried suspending the vacuum switch in a pot of water on a stove top? Have your vacuum lines attached out of the water to check air flow from. The water temp can more easily be  monitored compared to a heat gun. Just a thought .
Title: Re: Thermostatc vacuum switch
Post by: shelbydoug on June 30, 2020, 12:32:50 PM
No boiling water yet!

If it works the way I think it is supposed to, I actually like the idea of it closing the vacuum to the vacuum advance at idle.

It gives me tuning options.

Also I THINK that it switches at some point from engine vacuum to timed port vacuum. That's really what the question initially was getting at.

Either way, I'm ok with it. I probably will need to do the hot water thing to determine at what temp it opens and if it is simgle stage or dual.

I like the idea that it is still installed in the original thermostat housing. It is appropriate for a '68.

Now if I can only find a yellow plastic overlay for the ignition coil, like the battery top idea, I'd be happier.

Unfortunately, although looking great, the Marti Autolite spark plug wires crapped out already. Too bad. They looked great in the AUTOLITE cap.

I haven't thought about the original spark plug wires in 45 years. I was innocent then. I never realized how FREAKIN' BAD the original wire engineering was back then?  ::)
Title: Re: Thermostatc vacuum switch
Post by: J_Speegle on June 30, 2020, 01:15:57 PM
.........Bear in mind Ford had to meet federal emission standards in '67 and '68 depending on where the car was going to be sold. So the installation hook up does vary by application. You may find that it performs better in one of the other methods of hookup now that the car doesn't need to meet any specific specs.

Keep in mind that this depends on your local/state agencies and their law. Here in Calif the requirements are still there

But that doesn't have any affect of figuring out Doug's challenge
Title: Re: Thermostatc vacuum switch
Post by: Royce Peterson on June 30, 2020, 02:23:19 PM
Not just at idle. Any time the throttle is closed the vacuum signal to the distributor drops to a lower value, regardless of RPM. Decelleration for example. The only time the distributor vacuum advance would see manifold vacuum is during an overheat situation if it is all working properly.


No boiling water yet!

If it works the way I think it is supposed to, I actually like the idea of it closing the vacuum to the vacuum advance at idle.

It gives me tuning options.

Also I THINK that it switches at some point from engine vacuum to timed port vacuum. That's really what the question initially was getting at.

Either way, I'm ok with it. I probably will need to do the hot water thing to determine at what temp it opens and if it is simgle stage or dual.

I like the idea that it is still installed in the original thermostat housing. It is appropriate for a '68.

Now if I can only find a yellow plastic overlay for the ignition coil, like the battery top idea, I'd be happier.

Unfortunately, although looking great, the Marti Autolite spark plug wires crapped out already. Too bad. They looked great in the AUTOLITE cap.

I haven't thought about the original spark plug wires in 45 years. I was innocent then. I never realized how FREAKIN' BAD the original wire engineering was back then?  ::)
Title: Re: Thermostatc vacuum switch
Post by: shelbydoug on June 30, 2020, 04:47:34 PM
Not just at idle. Any time the throttle is closed the vacuum signal to the distributor drops to a lower value, regardless of RPM. Decelleration for example. The only time the distributor vacuum advance would see manifold vacuum is during an overheat situation if it is all working properly.


No boiling water yet!

If it works the way I think it is supposed to, I actually like the idea of it closing the vacuum to the vacuum advance at idle.

It gives me tuning options.

Also I THINK that it switches at some point from engine vacuum to timed port vacuum. That's really what the question initially was getting at.

Either way, I'm ok with it. I probably will need to do the hot water thing to determine at what temp it opens and if it is simgle stage or dual.

I like the idea that it is still installed in the original thermostat housing. It is appropriate for a '68.

Now if I can only find a yellow plastic overlay for the ignition coil, like the battery top idea, I'd be happier.

Unfortunately, although looking great, the Marti Autolite spark plug wires crapped out already. Too bad. They looked great in the AUTOLITE cap.

I haven't thought about the original spark plug wires in 45 years. I was innocent then. I never realized how FREAKIN' BAD the original wire engineering was back then?  ::)

That's ok with me. I don't see any disadvantage to that function.
Title: Re: Thermostatc vacuum switch
Post by: Corey Bowcutt on July 01, 2020, 08:32:06 AM
This has been a very interesting and informative thread.  I have a related question.  If you have electronic ignition does the vacuum advance still function?  I understand having it all hooked up to look correct but was wondering if it is actually doing anything?

Corey
Title: Re: Thermostatc vacuum switch
Post by: Royce Peterson on July 01, 2020, 08:41:33 AM
Electronic ignition (Pertronix etc) replaces the ignition points as a method of charging and discharging the coil. It has no effect on anything controlled by vacuum.


This has been a very interesting and informative thread.  I have a related question.  If you have electronic ignition does the vacuum advance still function?  I understand having it all hooked up to look correct but was wondering if it is actually doing anything?

Corey
Title: Re: Thermostatc vacuum switch
Post by: shelbydoug on July 01, 2020, 09:13:12 AM
Electronic ignition (Pertronix etc) replaces the ignition points as a method of charging and discharging the coil. It has no effect on anything controlled by vacuum.


This has been a very interesting and informative thread.  I have a related question.  If you have electronic ignition does the vacuum advance still function?  I understand having it all hooked up to look correct but was wondering if it is actually doing anything?

Corey

+1.
Title: Re: Thermostatc vacuum switch
Post by: shelbydoug on July 12, 2020, 11:19:33 AM
There are several hook up diagrams in the 68 Shop Manual.

By trial and error, I have determined that the engine vacuum goes on the bottom, the line to the carb "timed vacuum" is in the middle and the distributor vacuum advance goes on top.

If you put the distributor vacuum advance in the middle as the engine gets hot it will advance the distributor and raise the idle rpm about 400 rpms.

For me that doesn't work.

The tree seems to open at around 160 water temp. Apperently it is two stage? I don't know at what temp the valve distributes vacuum to the vacuum advance. I haven't gotten hot enough yet.