Correct source for ac vacuum

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projectmidnight74

projectmidnight74

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I am attaching pics. But currents I have no vacuum to move he doors when the av unit is switched to different settings. My mechanic bud is telling me to T into the trans vacuum line and not the brake vacuum. Thought I would come here for some options and opinions. Pics attached. Brake booster vacuum is currently being pulled from intake manifold.
 

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dsteelejr

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My ‘73 C20 has one of these on the intake manifold, where in your third pic you have a a fitting pointing straight up. One port goes to vacuum modulator on the TH350 and the other is for the black vacuum canister in your first pic.
 
dsteelejr

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Pic didn’t upload on my first post
 

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dsteelejr

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Get vacuum for your brake booster from the port on the back of the carb. Ditch that straight threaded fitting for 90° elbow and point it at the brake booster. It’s easier on the hoses. Just curious, what’s the big hose on the front of your carb on the right connected to manifold vacuum port?
 
projectmidnight74

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dsteelejr said:
Get vacuum for your brake booster from the port on the back of the carb. Ditch that straight threaded fitting for 90° elbow and point it at the brake booster. It’s easier on the hoses. Just curious, what’s the big hose on the front of your carb on the right connected to manifold vacuum port?
Click to expand...
Transmission vaccum port one to the left is vacuum advance to the distributor. Middle one is pcv
 
projectmidnight74

projectmidnight74

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dsteelejr said:
My ‘73 C20 has one of these on the intake manifold, where in your third pic you have a a fitting pointing straight up. One port goes to vacuum modulator on the TH350 and the other is for the black vacuum canister in your first pic.
Click to expand...
So in theory, I could just use a single one for the ac vacuum from that intake port and move the one that's there to the back of the carb correct.
 
dsteelejr

dsteelejr

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projectmidnight74 said:
So in theory, I could just use a single one for the ac vacuum from that intake port and move the one that's there to the back of the carb correct.
Click to expand...
It will work and that’s what really matters. If you want it less cluttered and done ‘properly’ how the factory had it then get a two port manifold fitting for AC and trans and move the brake booster source to the carb and plug off the carb port that is not used for vacuum advance.
 
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Yep, you can get those fittings in a couple of different configurations.
I just installed one to supply the brake booster and transmission vacuum.
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