I have a 66 switch pitch turbo 400 that is going behind a 66 425. The vacuum modulator gets its vacuum from the engine? But just above the vacuum modulator on the side of the transmission there is a steel pipe the size of vacuum line. What is it for? Do these two items connect some how?
Yes. At the area the bell and main case intersect about the 1-2 o" clock position is the vent tube. About 2 inches long bent down and aft.
OK that is what it is. What does it vent to? Seems like dust could get into the inside, as well as water.
It allows the case to vent pressure, and also dump excess fluid if you over-fill it. A bazillion transmissions with them, and unless your racing lobsters or up to your windshield in sand, water and dust should not be a problem. (But extra credit for thinking about stuff that might happen...)