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Discussion Starter #1
I have just replaced a th350 in my first car. It is a 1978 Chevy Cheyenne with a L6 250........ So the transmission has less than 200 miles on it and it wont shift to third when the truck is warm. It does it fine when the truck is cold. Also it makes a whistling noise when it shifts to 2nd and when it makes this noise again the truck is warm.
 

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Get in, sit down, hang on
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TH350's used a vacuum shift modulator.
If it's not connected, it does the "late shifting" thing ... even "governor" shifting into 3rd eventually.

It's doing it's job ... holding the trans in 2nd gear when there is low manifold vacuum (ie pulling up a steep hill)

You'll want to make sure that it's connected to straight manifold vacuum, and not a ported vacuum source on the carb.
 

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Discussion Starter #4
So i found it and the manifold vacuum goes to the egr and then goes to the carb which then splits to the vacuum modulator on the tranny. And the whistle sounds like a vacuum leak is there any way to find it with ease
 

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More for Less Racer
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With the engine running, spray a little carb cleaner around every suspected vacuum leak point, engine rpm will change when you hit the leak with the spray.

You can do the same with an unlit propane torch around every suspected leak point, rpm will go up when the propane is sucked in.

Just remember to shut the torch gas off when you aren't actually using it!!
 
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