Where do you attach a vacuum hose to the modulator valve on transmission of 305 Chevy?

There isn't a single, universally located vacuum hose connection for a modulator valve on all 305 Chevy transmissions. The location depends on the specific year of the vehicle, the type of transmission (TH350, TH400, 700R4, etc.), and even minor variations within those transmissions.

To find the modulator valve vacuum connection:

1. Identify your transmission: Knowing the exact transmission type (e.g., TH350, 700R4) is crucial. This information is usually found on a tag on the transmission itself.

2. Locate the modulator valve: This is a small, usually cylindrical valve on the side or top of the transmission case. It often has a single vacuum hose connection. It might be near the shift linkage or other components. A diagram specific to your transmission will be invaluable here.

3. Look for the vacuum line: The vacuum hose will be connected to either a nipple or fitting on the modulator valve. It may be a small rubber hose.

4. Consult a repair manual: A repair manual specific to your vehicle's year and model will have diagrams showing the exact location of the modulator valve and the vacuum hose routing. This is the most reliable way to find it. Online resources like Haynes or Chilton manuals are readily available.

Without knowing the year and transmission type, I cannot give you a specific location. Improperly connecting the vacuum line can lead to transmission problems. Use a repair manual or consult a qualified mechanic if you're unsure.