Rotary Mower in distress: shaft alignment?

First it started to howl when I was cutting tall orchard grass. Turned out the gearbox was full of water mixed with the oil. A little hole in the Allen screw on the top of the gearbox let water in.

With the water/oil siphoned out and new gear oil installed, it worked pretty well for about 30 hours until it dropped the nut off the main shaft (again). This time the dealer was on the ball and had two of the correct nut within 48 hours. Another five hours and it had worked up to a pretty good howl when I noticed today that the gearbox nuts were all loose.

I had dismounted the machine to save a crushed walnut sapling and I noticed the gearbox moving in a cycle as the shaft turned. I climbed onto the frame and tested a nut with my fingers. It tightened easily. I'll get to the reason for this eventually. As the gearbox orbited through its cycle, it was at times loud and at times much quieter.

When I got back to the house I tightened the bolts, only to be greated by a grating symphony from the rear rotor. A shaft joining a universal gear shouldn't need to be aligned, should it?

I'm tempted to loosen the nuts and play with the gear case while the shaft is turning, just to see if there is a sweet spot where it doesn't grate, but I'm afraid of making a mistake and getting eaten by the pto shaft.

Is it a big job to rebuild a gear case? I can't see any way to take it apart and I discovered last summer it has metric threads, an Italian product.

Thanks,

Rod

In a situation like that, with a mounted mower, I would think that the input shaft of the mower should be parallel with the output shaft of the tractor. The mower/box could be left or right, above or below the tractor's output shaft, and still be parallel. So long as it's parallel, the angles on each end of the shaft cancel each other out. When you have a shaft set such that the angles do not cancle each other, you get a lot of vibration and "hop" in the drive line. However, this generally leads to the U-Joint heating and failing. So....

I would look towards the bottom end of the mower. Is there a chance that there is a blade broken or otherwise out of balance? I don't know how that particular mower is set up, so I'm only guessing. If it has swing away blades, could one be stuck inwards, and have a smaller cutting circle, smaller orbit, and thus less "throw" relative to the opposing blade? When you say the gear box is orbiting, that makes me think it's a balance issue of some sort. I think the gear box, on your mower, is just the weak link that's now showing the symptoms of one problem or another. Don't know if I was any help, but it's some food for thought.... Good luck.

Rod

If they move smoothly and quietly, it may be time to put new bearings in the gearbox ( and seals ).