I can't find any info on this. Could someone tell me what the master vac hose is for. The hose with the check valve. It connects to the engine (right)? If you have a pic, that would be great. Any basic info on its function would be great. 71Z. Thank you very much, TimsZ

This is the only pic I could find, and I drew in that ghetto red line to show where it connects. You may have to blow up the picture to see it.

That hose is what provides the power assist for braking via the manifold vacuum (it connects to the rear of the balance tube on carbureted models-not sure about the later fuel injected ones). When you press on the pedal, the diaphragm in the booster helps apply pressure to the master cylinder. Without that assist, the brakes would feel like they do when the motor is off; i.e. you can still stop but you have to apply much more pressure, and probably more stress to the firewall and brake pedal.

The brake master booster holds vacuum created by the fuel system under acceleration and cruising. Vacuum drops when you decelerate/brake. The check valve is critical to keeping the vacuum in the booster at this time. A master vac unit with a leaky diaphragm or hoses will not hold vacuum and you get the braking problems described above.

Thank you very much, TimsZ