The 2 spd in my '46 is vacuum operated. Jeffery, I would think that if the vacuum part of the system is not operating at this time that rear would be in what ever position it was last shifted into before it lost vacuum. But, if you wanted to get it in high and drive it as is, I suppose you could manually shift it. Here is a bit of info from the 2 spd tech tip ( http://www.stovebolt.com/techtips/2-speed%20axle.htm
"Obviously the biggest thing different about the Advance Design and other older 2-speed rear axles is the vacuum shift unit itself. The easiest way to check the operation of the two speed (especially if the driveshaft is disconnected or the axle is out of the truck)is to use a vacuum source to shift the axle from one range to another while turning the pinion yoke by hand. You can feel the unit shift. A small hand operated vacuum pump is useful. On some units, the vacuum diaphragm can be removed and the unit shifted mechanically."