Tractor Repair: Drive line problem, broken shaft, clutch disk

Question
1963...Ford 4000...gas...Was operating and heard something snap loud...quit moving....though I snapped a axle....jacked up and spun each rear wheel by hand and can see ring gear turning through rear end fill hole...I can't see the pinion gear with out taking apart...no grinding when spinning wheels either...what couples the transmission to the pinion gear in the rear end??   Any idea what may have snapped??  Oh the pto works alright

Answer
  Start the engine and try to shift it into any gear without pushing in the clutch.  If you can grind gears, then you know the clutch and transmission input shaft are OK and the transmission is turning.  If it won't grind gears, then the input shaft is not turning and the clutch disk or input shaft could be broken.  You can either remove the transmission cover and look inside while turning the engine over, or split the tractor and inspect the clutch.  If it does grind gears, then the problem could be between the transmission and rear end such as a broken shaft or coupler.  The pto is independently driven off the flywheel so it is not affected.