1966 GT Modulator Vacuum Line - Ford Mustang Forum
 
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post #1 of 10 (permalink) Old 09-03-2012 Thread Starter
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1966 GT Modulator Vacuum Line

Hello All, Been reading the forum for a while and this is my first post...Love the forum..One of the best forums I read and participate in...Thank you!

just got my 66 GT coupe back from paint shop..Also has rebuilt 289 (boy she sounds great)...They forgot to hook up modulator vaccum line... I have a non original manifold and think the original line went to the carburetor...(No taps in the manifold)..I have the Holley 4160 carb...

So, question then, is where does the line hook up on the carb...I know which is the spark advance...The vaccumn line on the back of the carb is hooked to the hole in the valve cover. On the right side of the vehicle is another port at rear of carb. I{ hooked the modulator vaccum line to this one and it still doesn't change gears. On the lower front passenger side is a small port. And two ports about mid way on carb. The top is plugged off and lower one is open...(Saw one phote oin internet where there is line hooked between these two...

Reason for asking all this is car won't change gears abviously...

Thanks all for allowing me on the forum and for advice as well...have a great Labor Day..
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post #2 of 10 (permalink) Old 09-03-2012
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The modulator line should hook to the manifold, not the carb. I have never seen a manifold that did not have a vacuum port somewhere, so it might be capped off. What kind of manifold is it? If you have a brake booster, you can use a T-fitting to tap into manifold vacuum where the booster line connects to the manifold.

Bear in mind that I am not familiar with Holleys (I stick with Ford carburetors), and am not sure what that myriad of ports is for. I am only sure of the way Ford intended for it to work. If there is a way that Holley intended to run the modulator off the carburetor, I am ignorant of it and have never seen it, but that doesn't mean it can't be.

Joe
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'72 Grande, 351C, Motorcraft 2100, FMX, 2.75
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post #3 of 10 (permalink) Old 09-03-2012 Thread Starter
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I have the Edelbrock 289 Stroker Intake....Just looked again with a mirror....The vacuum line going from the valve cover is hooked to the back of the intake below the carb....Isn't that supposed to be hooked to the carb directly and not the intake....If that is the case that would free up the port on the intake for the modulator vacuum line....I think....Can someone conirm maybe? Thank you!
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post #4 of 10 (permalink) Old 09-03-2012
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Confirmed. Running PCV to an intake runner is bad juju. Since there is airflow through it while the engine is running, it leans out whatever cylinder it's going to. There is no actual airflow through the modulator line, though, only a vacuum signal.

In short, you are absolutely correct.

You may have to adjust your idle mixture slightly richer once you have it hooked up correctly, since there will be slightly less venturi vacuum pulling fuel through the idle circuit. (Unless that's just an Autolite/Motorcraft thing!)

Joe
'65 Coupe, 302, Autolite 4100, C4, 2.80
'72 Grande, 351C, Motorcraft 2100, FMX, 2.75
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post #5 of 10 (permalink) Old 09-03-2012
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There are two "types" of vacuum. Manifold and ported. Manifold vacuum comes from the piston going down in the cylinder with an intake valve open. Ported vacuum is simply from the air moving down the throat of the carburetor.
You want to connect the modulator tube to manifold vacuum. This can sometimes be found on the carb also. Find a rubber cap and see if it has a lot of suction at an idle. If so that is manifold vacuum.

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post #6 of 10 (permalink) Old 09-03-2012 Thread Starter
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Well, I changed the line from the modulator to run off the intake....Car still won't change gears? What should I try next?
Thank you!
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post #7 of 10 (permalink) Old 09-03-2012
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I would use a hand vacuum pump to check the modulator and line for leaks and blockages. Start with the simple (and best of all, easy & cheap!) things first.

Joe
'65 Coupe, 302, Autolite 4100, C4, 2.80
'72 Grande, 351C, Motorcraft 2100, FMX, 2.75
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post #8 of 10 (permalink) Old 09-04-2012
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u may need a new modulator valve if the vaccuum signal is good and there are no blockages or leaks in the vacuum line. Just a question before you do that, what was done to the tranny while the motor was out? was it in good shape before?

One last thing, make sure the fluid level is correct if you changed the converter or if you emptied the old one.

The modulator valve can also be adjusted through the vacuum nipple to increase or decrease the shift point.

hope you get this resolved quickly.
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post #9 of 10 (permalink) Old 09-04-2012 Thread Starter
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I had the tranny overhauled before the engine was done...like 4 years before and quit working on the car....Tranny has maybe 5 miles on it....I doubt the modulator was changed....I am going to try vacuum test, then try adjusting the modulator, then....if that doens't work keeping asking question on the forum...Will post an update.....Thanks again!
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if it has been sitting for 4 years, u may have rust on the bands and they are stuck to the planetary gear housings, or valves that are stuck preventing proper fluid movement for shifting. run a transmission conditioner product like lucas. or transx or trick shift fluid to help loosen things up. u might have to loosen up the bands to free them and then readjust.
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