JD 720 Mo/Co.. need help

Have a John Deere 720 Mower Conditioner, during first cutting this year, on the last field, the sickle cutter bar stopped moving. The reel and the rolls move, but not the cutter bar. I should note that the mowing conditions in that field were real wet, even muddy in some parts.
My local JD dealer wants to tell me that there is a driveshaft that runs from the initial gear box, down to the gear box that runs the cutter bar, but it is belt driven. I tightened the belt, that didn"t work. The pulley that runs the cutter bar gear box moves MAYBE an inch back and forth when you grab it and move it with both hands.
Does anyone know of a shear bolt/pin or a key that may have broke? I"m really hoping it"s not the gear box, I really can"t imagine that would be a cheap fix. Either way, second cutting is shot, making 2013 the worst year for hay in our books.

As always, any help is appreciated

Well first off whoever you talked to at the dealer ship thought you have a disk MO-CO. They do have a drive shaft that runs the cutter bar gear case. Now for your problem.

1) Remove the sickle drive bolt/pin from the gear case arm. Just like you do when you remove the sickle.
2) See if the gear case will turn now. If it does then your drive system is OK. Your sickle is stuck in the guards. I have seen them do this is wet muddy conditions. There just gets to be so much crap in the guards that it wedges the sickle bar tight. I have had to pull the sickle out with another tractor before.
3) If it still will not turn. Loosen the Sickle bar drive belt. See if the knife gear case will move. If it does not then you have bearing out in it. If it moves you have a problem in the main gear case.


I would bet on the sickle just being stuck tight with junk/mud/wet grass. It will do this worse with worn guards or lose hold downs. The stuff starts to build up under the knife and it just gets worse. If it is the sickle stuck and you are back home just wash it out with a pressure washer. Then remove the sickle and repair any worn parts for next year.

Second to JD's info!

JD I can't thank you enough. The problem was exactly that there was junk built up. What a relief I had when that gear case moved freely. I ended up taking the sickle bar right now, along with all of the guards. I still have a handful of bolts that I will end up cutting off. Again, what a relief. Thank you. You saved me a lot of time, headache, and money!