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