Re-routing TH350 Vacuum Modulator Vacuum Line...What Size Vacuum Hose ?

Tynan918

Royal Smart Person
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Aug 2, 2021
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I'm re-routing my vacuum modulator vacuum lines because it was 3 way routed into the vacuum canister ball on the passenger side of the engine and then to the full vacuum port on the carburetor...

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I'm told this is wrong and my transmission vacuum modulator isn't getting the full vacuum requirement being routed like this. I was told to get an intake manifold tee fitting and run the vacuum modulator straight to the T fitting on the intake manifold to provide the full manifold vacuum required for the modulator.

I bought this intake manifold tee fitting, one end is 3/8 for my brake booster and the other end is 1/4 for my transmission vacuum modulator.

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I also bought 10' of 1/4 vacuum hose, but after removing the old hoses I see the hose size is 3/16...

Can I still use the 1/4 hose on the vacuum modulator or will I need a reducer fitting at the vacuum modulator to make it fit the vacuum modulator nipple ?
 

mikester

Comic Book Super Hero
Mar 10, 2010
2,649
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Small town NY
I dont remember the size of the hose going to the modulator. Its been a while but I can probably let you know tomorrow. A few things though. The fitting on the manifold will feed the modulator and the vacuum ball at the same time with a plastic T fitting inline. The larger nipple on the fitting should go to the booster.
In the video I see a PCV valve. What is that hooked to ? And why do you have a vacuum gauge ? The other thing I noticed. It looks like you have something going on with the vacuum line to the distributor. Whats that about ? You also need to make sure the line going to the modulator will be away from the header and exhaust.
 
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Tynan918

Royal Smart Person
Thread starter
Aug 2, 2021
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The fitting on the manifold will feed the modulator and the vacuum ball at the same time with a plastic T fitting inline.
What is the ball used for ? I'm told to eliminate it because I don't have AC...

In the video I see a PCV valve. What is that hooked to ?
PCV is hooked to the back of the carburetor.

And why do you have a vacuum gauge ?
Adjusting my vacuum advance canister.

The other thing I noticed. It looks like you have something going on with the vacuum line to the distributor.
Disconnected and plugged it off to set base timing and adjust the vacuum advance canister.
 
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airboatgreg

Comic Book Super Hero
Oct 2, 2016
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3?16 to 1/4" Run it off the tee from the intake manifold or rear of carb. The vacuum ball is a reservoir to allow the heater to move doors to defrost
 
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