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Old 10-24-2007, 08:46 PM
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Th350C Modulator hook up

Is it alright to run all vacuum rubber hose from Modulator to Carb? I see pictures of trannys that run a short hose on each end of a steel line. Is this mandatory for some reason?

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Old 10-24-2007, 09:05 PM
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The steel is more robust. Won't collapse. Harder to cut, burn, kink, or melt.
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Old 10-24-2007, 09:28 PM
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Quote:
Originally Posted by bartamos
Is it alright to run all vacuum rubber hose from Modulator to Carb? I see pictures of trannys that run a short hose on each end of a steel line. Is this mandatory for some reason?
The hard line is way less prone to develop leaks. A leak in the vacuum source creates BIG problems for a Turbo 350 ( or any transmission with a vacuum modulator )

It also looks a good bit more professional and less " rigged "
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Old 10-30-2007, 06:31 PM
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All of the above, plus the fact that the factory hard line is designed to prevent fluid from being gulped through the intake in the event of a modulator diaphram failure. The hard line is raised at the point of entry similar to a reverse pea trap in your lavatory j pipes. We had a SB block Camaro that would blow a huge puff of smoke out the exhaust at highway speeds every two miles or so. I finally checked the modulator and there was the problem , busted diaphram. Use the hard line if you can find one . Buy one for a mid eighties 1/2 ton pick-up with a TH350 .
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Old 10-30-2007, 07:19 PM
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Thanks much. I also want to know if it is OK to attach at the rear of carb. I see some attach into the manifold? any difference.? I will get some brake line and custom bend it for my application. 1974 454 Big block/Th 350 in a 1956 GMC Carryall. Keep the info coming.
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Old 10-30-2007, 07:28 PM
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the modulator needs direct manifold vacuum hook up
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Old 10-30-2007, 07:43 PM
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So that big honkin vacuum port at the rear base of the carb where I have a tee, one side to brake Diaphragm and other to tranny Modulator is no good? Should I find a threaded port on one of the intake channels?
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Old 10-30-2007, 08:57 PM
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Quote:
Originally Posted by bartamos
So that big honkin vacuum port at the rear base of the carb where I have a tee, one side to brake Diaphragm and other to tranny Modulator is no good?


Should I find a threaded port on one of the intake channels?

that is correct, it is best to not tee off or share vacuum with another item for the trans modulator.
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Old 10-30-2007, 09:23 PM
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Manifold

Yes, it needs to be hooked directly to the intake manifold. Some factory set-ups actually have restrictions in the line to "meter" the vacuum signal . I use straight full-time manifold vacuum through a small nipple around 1/8 " I.D.
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