Vacuum source turbo 400

Discussion in 'The "Juice Box"' started by suntreemcanic, Jul 13, 2020.

  1. suntreemcanic

    suntreemcanic Well-Known Member

    Where is the proper source for vacuum to my Turbo 400 switch pitch transmission. My engine is a 425. Do I use a port on the intake manifold or at the base of the carburetor? The rebuild manual does not discuss this.
     
  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    It doesn't matter at all, as long as you connect it to manifold vacuum and you have a secure leak free connection. Stock, it connects to the back of the intake manifold same as later Buick V8 engines. From the 1966 Chassis Manual,

    1966ST400ModulatorLine.jpg
     
    Last edited: Jul 14, 2020
  3. telriv

    telriv Well-Known Member

    It really doesn't matter as long as it's getting vacuum. On an original TH400 with an AFB the vacuum connection was at the right rear of the carb. The fitting that fit that connection only had a approx. .060" hole to allow the nec. vacuum so that changes in throttle input wouldn't have such a huge effect causing a constant up & down shifting of the modulator valve.
     
  4. suntreemcanic

    suntreemcanic Well-Known Member

    I have access to the intake vacuum through an 1/8 inch pipe fitting on the intake manifold in front of the carburetor. I like the idea of not constant shifting. I will measure the diameter of the passage hole in the 1/8 pipe plug. Thanks Larry and Tom! Oh Tom I think in a couple more weeks I will try out those pistons of yours, I should have my car on the road finally.
     
  5. telriv

    telriv Well-Known Member

    Larry,

    The pic posted is NOT a "NailHead" as the starter is on the right side not the left as in a "Nail".
     
  6. telriv

    telriv Well-Known Member

    suntreemcanic,

    I will need ALL the nec. specs. for pistons as they are ALL CUSTOM MADE for your particular engine specs. & can ALSO be customized for your particular build at NO EXTRA COST. It's usually a 4-6 week time frame.

    Tom T.
     
  7. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    I got it from the 66 Buick Chassis Manual. How about this one?

    1966ModulatorConnA.jpg
     
    Last edited: Jul 14, 2020
  8. suntreemcanic

    suntreemcanic Well-Known Member

    Tom, I bought a set of your pistons from you about 6 most ago. I have ran the engine on a stand but I hope to be driving the car in a couple weeks. I have a 2500 mile trip for it in September.
     

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