Tractor Repair: Case 1070 powershift transmission, mechanical repair, woodlot

Question
I have a Case 1070, serial # 8678810- 5280 hrs, with a transmission problem.  The tractor has no forward or reverse motion in 4th gear.  A couple of weeks ago, we were bringing home a load of logs.  My wife left the woodlot and was heading home in 4th gear, 3rd range.  Two miles into the trip, she heard a grinding noise coming from the transmission.  She stopped the tractor and shifted into 3rd and brought the tractor home without hearing any further noise.  I then checked the tractor to determine the problem.  Hydraulic oil level was good.  Tractor moved forward & reverse in 1st, 2nd & 3rd in all three ranges but still no motion in 4th gear.  I would appreciate if you could give me some other diagnostic suggestions for the problem and items to check.  I do have a repair manual for this tractor. Also, I do all of my own mechanical repair on my equipment.  Thanks for you time and I look forward to your answer.

Answer
  That's a little unusual, it's usually the powershift that has problems, not the range transmission.  Check the shift shafts on the transmission cover and make sure they are moving OK when shifting into and out of 4th.  If it looks OK, then I don't think you have any choice but to remove the transmission top cover so you can see what happened inside.  It's not very much fun to remove the cover, it's big and thick and heavy and won't fit through the trap door in the floor so it has to be slid out the side.  Once it's removed, you can see the gears, shift rails and forks to see if something is broken.