Yes, they default to low with a spring. Vacuum pulls them into high. I just stick something in the linkage at the axle to keep them in high. The factory recommendation is to park them in low range, but that is because the e-brakes were a joke and low range gives a little more engine braking power. Of course you are probably never going to park an over loaded truck on the side of a hill anyway. A chock block is the best parking brake you can get anyway. I just block off the entire vacuum circuit to the two speed. That eliminates a lot of vacuum leak problem and trying to fix stuff for which parts are no longer available.
Jerry, my Emeryville was a 5 and 3. The Eatons were air shift and the suspension was a Hendrickson rubber pad. I could out pull trucks in my class that had Roadrangers because I always had just the right gear. But using intermediate sure took its toll on power dividers. In fact I usually carried a spare. There were even times I had to make thrust washers for the planetary gears out of beer cans. The planetary gears would eat into the housing to where they would jump the sun gear on a hard pull. A naturally aspirated Cummins with a back drop manifold sure sounded pretty with a 5 and 3 behind it. The contacts on the shift know would carbon over from shifting so much. I could take the shift knob apart while I was driving and file the contacts with a match box. I with I would have had a recorder back in those days to record the sound and photograph the flame coming out of my stack. I drove that thing daily for about 10 years.
