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75 chevy tranny shift...

Discussion in 'GM Powertrain' started by dzmolek, Dec 1, 2009.

  1. dzmolek

    dzmolek New Member

    hi,
    i have a 1975 chevy 3/4 2x4 that i took pulled the engine and tranny out of and put a 350 out of an 1986 into it and used the 1975 tranny on it. I got the truck running before i pulled the old engine and the tranny shifted fine into all gears. Now that I replaced the engine and put the tranny back in it will not shift unless u manually shift it on the column. Otherwise if you leave it in D and take off it wont shift out of 1st. I hooked up the kickdown cable onto the carb just like it should be. Can anyone help me with this problem? Is it a lack of tranny fluid? or is the tranny shot? Thanks for your input....
  2. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    You probably have a missing vacuum line to the I assume 350 transmission. Make sure you have manifold vacuum to the modulator. When you pull the line off the modulator the engine should speed up. If not then you have found the problem.
  3. dzmolek

    dzmolek New Member

    where on the tranny is the modulator located?
  4. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    On the back of the transmission passenger side.

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