I finally had a little bit of time to run out to the farm to look a the brakes. I was mistaken about the two speed not having a diaphragm. It does have a small one. The supply line to the rear end does come out of the hydrovac though. You can see in the pic. A rubber hose comes out of the hydro into a tee fitting. One goes to the breather and the other goes to the two speed. When I got in the truck, I pumped up the brakes to get my pedal towards the top, then started the truck. I didn't feel any difference in pedal. Does that mean the hydrovac is bad? I did notice (and you can see in the pic) that there is a date written on the unit that make me believe if was serviced/overhauled in 2014. When I press the brakes with the engine on, I notice an change in pitch in the engine like it is using vacuum. When I turn the engine off and hit the brake a couple of times I can hear it hiss through the breather which is installed right by the seat, just aft of the door.
