Tractor Repair: transmission, shift forks, snap rings

Question
474 international ser#2310040B101776-X- with syncro mesh transmission. transmission will go into high range and low range at same time and jams transmission. we have adjusted and check shifting gates on the outside of the transmission but this did not fix problem. we then unhooked shifting mechanism and shifted levers by hand. when this is done you can see both high and low range levers moving together and letting both engage at same time. what do you feel is the problem and what would resolve this issue. thank you for your time.

Answer
  Both shift forks in the range transmission slide on the same shift rail.  The shift rail could be broken or the snap rings that hold it in place could have broken and fell off allowing the entire rail to move, which could move both forks at the same time because of the detents.  The top cover will have to be removed to see what is wrong.