# What am I missing here???



## 1968 Q8 (Jun 9, 2011)

The first pic is of the engine from the seller's ad when we bought the car.

The second pic is of the engine the night we picked it up.

In the first pic, on the right side of the t-stat housing, there is a post with what looks like vacuum lines attached, but when we picked the car up, no post or lines, just a wire.

Can someone let me know what WAS there...

Thanks.


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## chuckha62 (Apr 5, 2010)

In the first pic, it appears that the sender is on the driver's side of the T-stat. Did they swap the sender and the vacuum tree from one side to the other?


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## rickm (Feb 8, 2012)

hey, thats a thermostatic vacuum control switch. those lines go to vacuum advance on distributor and carb. see if the nipples for those hoses are now plugged. whats this guy tryin to pull on you? temp switch mounts on drivers side of intake.


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## rickm (Feb 8, 2012)

there is another component in that system on pass. side of intake between dist. and carb. it changes vacuum from ported to manifold for full dist. advance.


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## 1968 Q8 (Jun 9, 2011)

So, does this mean my vac-advance isn't working? here's a few more pics.

pic 1 - Is that the temp guage sending unit on the left of the t-stat, if so, why doesn't my temp guage in the rally cluster not work? Doesn't really matter, cause there is an a/m temp guage under the radio...is that what's in place of the vacuum tree???

pic 2 - the metal bracket beside the carb, is that where the lines SHOULD be?

pic 3 - vacuum line in the centre is from the brake booster, and blue stripe is vacuum source for hideaway system

pic 4 - this line has a check valve and runs from inside the firewall straight in to base of the carb the intake.

Where shoul I be seeing the vac-adv lines? Do you guys see them at all? Would I be experiencing driveability issues....cause it still hauls ass...


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## rickm (Feb 8, 2012)

should have already asked but what year is your gto? looks like you got a g.m. h. e. i electronic ignition distributor.


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## 1968 Q8 (Jun 9, 2011)

1968 400 CID, what is h.e.i. ?


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## rickm (Feb 8, 2012)

thats why all those components are missing. he changed to electronic ignition. there no longer needed. im sure i runs nice but its not stock. dont know if it matters to you.


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## rickm (Feb 8, 2012)

google general motors hei electronic ignition or look in summit racing .com


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## 1968 Q8 (Jun 9, 2011)

No kiddin' eh...

ah well, no biggie.

But does that mean the advance is electronic? where would the signal come from to advance/retard, the module i guess?


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## rickm (Feb 8, 2012)

dont be bummed out about it . alot of guys change over to it. it actually performs very well and is reliable. i just find it odd he changed it in the middle of selling the car. if your not a stickler for originality. happy motoring and good luck with your gto !


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## 1968 Q8 (Jun 9, 2011)

Thanks for all your help Rick, i really appriciate it!


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## BearGFR (Aug 25, 2008)

Ok... that valve with all the lines in the very first photo in your thread is a temperature sensitive vacuum control switch. It's intended to regulate the amount/type of vacuum that the vacuum advance mechanism on the distributor "sees" depending on the temperature of the engine. In your later photos, I see what looks like two electric temp sending units. Did he perhaps add a temperature gauge to the car? A gauge needs a different kind of sensor than a switch ("idiot light") does so perhaps that's what's going on here - he left the light intact and added a gauge, and needed an additional spot to install the gauge sensor so he used the port for the vacuum gauge.

It's only a problem if you care tremendously about whether the car is 100% original or not. With the original vacuum control in place, it only "did things" when the engine was cold. Once the engine gets up to normal operating temp it effectively did nothing, so don't worry that not having it is doing bad things to your engine. Just make sure that the vacuum advance mechanism on your distributor is connected via hose to a vacuum source on your engine -- there's a big debate over whether the source "should" be a ported or a non-ported source -- but the real answer is to try both of them then use whichever one your engine seems to "like" the best. i.e. best throttle response, best idle quality, best mileage, etc.

Remember there are two "kinds" of advance in a normal distributor (including non-computer controlled HEI). There's vacuum (comes into play only at part throttle and is intended to improve economy, emissions, etc) and mechanical/centrifugal (varies depending on engine RPM only and is used to "time" the spark so that it occurs at the optimum point in the compression stroke for getting a good burn for optimum torque production).

Both kinds were replaced on engines that have complete computer control of ignition timing.

Bear


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## lars (Sep 28, 2004)

Bear makes some good, accurate comments. Just a couple additions to his excellent evaluation:

The vacuum control valve you are missing is actually a fairly useful and neat piece of equipment: When the engine is cold, the valve prevents any vacuum advance from being applied to the distributor: Retarded timing (no vacuum advance) makes the engine run hotter, so this assists in getting the engine up to temperature as quickly as possible (thus lowering emissions by reducing the amount of time the engine is not at operating temperature). Once the engine hits normal operating temperature, the valve shuttles over to the "ported" vacuum position, applying ported vacuum to the vacuum advance. Ported vacuum does not provide any vacuum advance at idle, thus running combustion temperatures up higher for lower emissions. Ported vacuum will apply normal vacuum at light throttle cruise as the throttle blades are slightly opened, so you still get the mileage benefit of vacuum advance at cruise. The third position is the "hot engine" position: If the engine temp goes too high, the valve will apply straight manifold vacuum to the vacuum advance, even at idle (like in stop-n-go traffic), thus lowering engine temperature and prevent overheating. Once engine temp is back to normal, it will cycle back to the "ported" vacuum position again.

For a paper discussing the principles and benefits of vacuum advance (ported versus manifold vacuum), drop me an e-mail request for my paper on "Vacuum Advance Control Unit Specs and Facts." This is a paper I have written jointly with known automotive design engineer Duke Williams - we are both contributing tech authors for several autmotive technical journals and publications. You can also request my "Engine Vacuum Explained" tech paper for an overview of the different types of vacuum and their uses. These papers dispel some of the myths and incorrect information floating around about vacuum advance and its operating principles, and the papers are currently used by some of the automotive technical colleges as teaching aids on this subject matter (I'm on the Education Curriculum Board with Lincoln Tech).

I would really recommend you try to locate one of the functional vacuum switches - see if the guy who sold you the car kept it in his garage. It's nice to have all the original equipment for these cars, regardless of how you choose to hook up your vacuum advance. The fact that you have an HEI distributor is completely irrelevant for vacuum advance control - it operates the same as your original points distributor (see if your seller has the original distributor as well...)

Good luck with the car!

Lars Grimsrud
[email protected]


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## 1968 Q8 (Jun 9, 2011)

Wow. Well done guys. Thanks to all of you who responded, as I am of the "younger enthusiasts" I have very little knowledge of these systems, thanks for the tech lesson!

Happy motoring!


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