Powerglide vacuum hose purpose?

[Hair]

My power glide has a vacuum hose and it is not hooked up at all, just hanging there, but it still shifts into high gear just fine, so it seems. So what does the vacuum hose do?

[rsavage]

For modulator valve. Helps transmission to determine shift points based on loads etc. Google it. Hook it up.

[AussieinNC]

The modulator should be plumbed using a rubber hose onto the modulator, transitioning to a metal tube heading up the the intake manifold, where it transitions back to a short section of rubber tube that fits over the small manifold fitting that is ported to full manifold vacuum.

The modulator may have been leaking trans fluid via its rubber diaphragm...if your engine start blowing smoke after you connect the modulator, change it out. If you buy a new one, choose a "Red Stripe" adjustable unit...suggest a
https://www.amazon.com/Rostra-51-030.../dp/B002NLRQ24

If you remove the old modulator, you will find a removable hollow pin in the inner end of the modulator...make sure you place the tube inside the new modulator before your screw it in...make sure you use a new gasket.

At the manifold end, make sure the port hole into the manifold is clear and open to the manifold...you can use a paper clip to probe the fitting.

Hope the above helps