Bad gear box on mower deck?

[Yellowvette]

I have a 60" John Deere lawn mower deck and while mowing the blades stopped working. After taking the deck off the mower I have found that the PTO does run when the switch is pulled. But when I spin the PTO shaft attached to the gear box, the blades do not turn? If I turn the blades they all turn by hand very easily, but every so often when turning the blades the PTO shaft jerks a small bit? Does this mean that the gear box has some broken gears in it? Is the only fix a new gear box? This gear box does not have any kind of shear pin to look for does it?
Thanks for any help anyone can give, the gear box is expensive, but if it is what I need, that is what I need!

 

[yankeerider]

Welcome to TBN! Does your deck have 3 blades driven by a belt? What condition is the belt in? How tight is the belt? I doubt the problem is in the gearbox, because those gears are pretty stout. It's more likely a sheared key and roll pin on the gearbox output shaft. When that happens, the pulley that drives the belt tries to fall off the shaft.

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[GManBart]

I'm not familiar with that deck/gearbox...do you have a picture of it? If you do need a new gearbox, don't assume it has to come from a Deere dealer. It very well may be a gearbox made by another company, like Omni, who make most of the mower/cutter gearboxes out there. If that's the case, you can buy the exact same item for much less than if you get it from a dealer.

While it's a different setup entirely, I just replaced the gearbox on a King Kutter brush hog, and paid only $175, delivered, for a factory new, OEM Omni gearbox, which is what it had originally. The only difference is the paint, which you can fix easily. If I'd bought the gearbox through KK, it was something silly like twice as much!

 

[yankeerider]

GMan, I replaced the output shaft on the gearbox of my Deere 60" mower. The shaft was about $80. The damage was external to the gearbox where the output pulley had been wobbling on the shaft after stalling the tractor when the blades hit rock ledge. The expensive part was that pulley at $140.

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[radioman]

I'd check to see if you have a shear bolt . that bump/chatter you feel could be the shear bolt rubbing at that one spot inside the pto shaft. I would see if you can turn the blades and see the shaft spin on gear box. OR it might be a sheared keyway/woodruff key on the pulley wheel.