Vacuum Line Connections - Pontiac GTO Forum
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post #1 of 10 (permalink) Old 07-06-2014, 08:29 PM Thread Starter
 
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Vacuum Line Connections

I finally put the stock intake and Qjet on my 68' LeMans 350 with 2 speed and A/C. I followed this attached drawing I found for the vacuum hookups...is this right?

With this hookup my 2 speed trans is not down shifting when you stomp on the accelerator. I have the trans vacuum line hooked to a 3 nipple deal threaded in the backside of the carb. one straight out is for power brakes that I dont have yet and the other 2 come out the side one for the trans and the other is hooked to the #2 line from the TVS.
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post #2 of 10 (permalink) Old 07-06-2014, 09:21 PM
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The transmission vacuum modulator is used to activate the up-shift points on the transmission, the kick down circuit for a st-300 is activated by a switch attached to the accelerator pedal. Do you have a wire connected to your transmission?

Randy


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post #3 of 10 (permalink) Old 07-07-2014, 08:33 PM Thread Starter
 
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Yes I have a wire attached to the side of the trans. When the car did this before it turned out to be a blown fuse in the fuse box marked Trans and Gauges.

Here are some pics to go along with my above post as to how the vacuum lines are hooked up. Do you see anything out of place?
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post #4 of 10 (permalink) Old 07-08-2014, 03:46 PM
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05 nailed it. The vacuum connection is what makes the transmission up-shift early at part throttle ("early" meaning earlier than it would if you had your foot in it --- if you want to prove it's working, disconnect that vacuum line, plug the leak, and drive the car. You'll see what I mean.)

If you aren't getting the downshift, check that fuse again - and the wiring to the kickdown solenoid on the transmission.

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post #5 of 10 (permalink) Old 07-08-2014, 06:16 PM Thread Starter
 
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Ok, thnx Bear I will double check the fuse and move down the line if it checks out ok.

Also this has been converted to HEI so single vacuum hookup on the advance

The Intake and Qjet are a 1969 and I assume that my 1968 TVS is just fine with it??
Do you know how I should plumb my vacuum lines? I can't find a diagram any place.

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post #6 of 10 (permalink) Old 07-08-2014, 07:46 PM
 
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here is a link to some diagrams, they are for a firechicken, but they are similar.

68 Vacuum Diagrams (Again) | Drivetrain | Firebird Classifieds & Forums (1967, 1968, and 1969)
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post #7 of 10 (permalink) Old 07-08-2014, 08:15 PM Thread Starter
 
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I may have found my down shifting problem. The accelerator pedal is not engaging the kick down switch on the back side. I don't think it is travelling far enough because I am using the throttle cable and cable bracket as well as the throttle arm from my 2 bbl on my Qjet. I have been trying to find out if there is a difference in these parts and so far I don't find any listing for 2 bbl but all the listings I find specify the new parts are for 4 bbl.
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post #8 of 10 (permalink) Old 07-08-2014, 08:20 PM Thread Starter
 
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Those vacuum diagrams are fantastic thank you so much it helps a bunch.
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post #9 of 10 (permalink) Old 07-28-2014, 09:13 PM Thread Starter
 
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Ok, figured out the downshifting problem...I had to change the throttle arm on the side of the carb and change the throttle cable bracket. Turned out the accelerator was not travelling far enough to engage the kick down switch on the back of the pedal. had to change the cable bracket because the on from my 2 bbl intake did not reach down to the intake bolt where it mounts.The throttle arm is what really did the trick allowing the cable to hook up properly and travel the way it should. Everything functions now.
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post #10 of 10 (permalink) Old 08-14-2014, 06:57 PM Thread Starter
 
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This may not be anything new for you guys but I found that the TVS is marked as to where the vacuum lines get connected. If you look closely next to each port on the TVS there are initials printed that tell you where they go. Such as, CA=carb advance, CR=carb retard etc..
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