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TH400 modulator on '72 350

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Old Oct 1, 2021 | 02:56 PM
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Default TH400 modulator on '72 350
I replaced rather than adjusted my modulator, and instructions for the new one stated that 'great care was taken to adjust this to factory specs', however now the transmission will not shift out of 1st gear. Just wondering if the new one is mis-adjusted and that enough can be done adjusting to get this tranny to shift again. I have the adjustment instructions and wonder is any members can tell me how much change will be realized by turning the screw 1 turn, 2 turns. I believe I need to turn the screw clockwise to get it to shift and shift smoothly. Thanks for any help with this.
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Old Oct 1, 2021 | 03:40 PM
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Did you hook up the vacuum line? That's all I could think of.
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Old Oct 1, 2021 | 04:35 PM
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Originally Posted by 69FASTFUN
Did you hook up the vacuum line? That's all I could think of.
yes, it's hooked up.
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Old Oct 1, 2021 | 05:15 PM
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If you didn't already put a hand held vacuum pump on it and see if it holds vacuum. also check your vacuum line all the way to the the other end at the engine and make sure there are no leaks. one time about 25yrs ago when i had toi have my trans replaced the shop forgot to connect the other end of the vac line to the manifold and it would not shift out of first at least not up to 5000rpm.
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Old Oct 1, 2021 | 08:43 PM
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jChances are the "new" modulator should be used as a door stop... Take it back and get one that works.
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Old Oct 1, 2021 | 08:54 PM
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Originally Posted by 7T1vette
jChances are the "new" modulator should be used as a door stop... Take it back and get one that works.
dang it, didn't occur to me; sure hope I can find the old one, at least it worked better than it's replacement
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Old Oct 1, 2021 | 09:06 PM
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Originally Posted by 69FASTFUN
Did you hook up the vacuum line? That's all I could think of.
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Old Oct 1, 2021 | 09:13 PM
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Another vote for the vacuum line......possibly blocked somehow. If it's hooked up, the modulator will generally work throughout its adjustment range, with the shift points just changing a little.
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Old Oct 3, 2021 | 01:14 PM
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Originally Posted by C3 Stroker
Another vote for the vacuum line......possibly blocked somehow. If it's hooked up, the modulator will generally work throughout its adjustment range, with the shift points just changing a little.
wasn't blocked, the connection from car to new rubber hose on modulator was bad, was not holding vacuum because of connection sizes. Good to go now
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Old Oct 4, 2021 | 10:35 AM
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Glad it was an easy fix. Also glad you didn't get a 'lemon' with the new modulator.
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Old Oct 4, 2021 | 11:05 AM
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Originally Posted by 7T1vette
Glad it was an easy fix. Also glad you didn't get a 'lemon' with the new modulator.
You and me both brother
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