Hey Weave,
I was trying to think of how to best explain it without a lot of detail, here I go with a long version again.
The range selector is mounted high & to the drivers side on all Fuller transmissions. On yours, you should have two airlines (tiny as heck) that run from the shift lever down to the trans. For people running 13 spd Fullers, your setup with be different with 4 lines, 2 to the range selector and 2 more to the overdrive selector on the shift knob itself. Or 4 lines to the shift knob period.
First and foremost thing that causes a range selector to fail is, 1) Lack of lubrication for the range selector. The Orings are "buna n" and without the required lubricant going through the trans air system they will deteriorate over a period of time. There should also be an air system filter (very small in size) mounted to the trans that distributes the silicon based oil.
You can recognize it by the shape, it's almost like the ones you find on a commercial shop air system. If the filter plugs, which is really rare, or pressure regulator been tampered with those can lead to the range selector not working also. Usually as long as the primary air system is clean & dry you should not experience that kind of problem.
2)Broken airline at the selector or somewhere along the airline circuit to the range selector or 3) O ring problems at the range selector controller or shift knob for 13 over's. The other options would be an internal trans problem, bent range selector lever or fork.
Hope this explaination helps pardner.
