there were some problems with the trans in late 84 and 85. most had to do with the mainshaft breaking or gears going out. it sounds to me like your shifting mechanism is gone. that happens too. tearing into the trans can be done if you are a good mechanic, but is best left to someone qualified as the re-assembly requires some precision spacing, etc. i, too have the same xlx i bought new in 85 and have had the trans rebuilt with mostly andrews gears. i hope this helps you. good luck.