Bad vibration/ Kubota RC72R-F30 deck

[Capt.Ron]

I have an F2560E, my deck is RC72R-F30. It's vibrating really bad. It seems to be the PTO, gear box or both.
It's possible to be an out of balance blade or bent spindle but even with the belt off the gearbox still vibrates. I tried removing the shear pin/bolt that attaches the PTO shaft to the gearbox and there still seems to be some vibration. The U-joints don't seem to have any noticeable wear so I can imagine those are bad.
It's so bad it's caused one of the mounting bracket tabs to break off where it bolts to the deck. I welded it and put new bolts all around. Now the tab has broke next to my weld.
Has anyone here experienced this problem and what may I ask did you find?

 

[Roadworthy]

It's unclear whether this is a new problem or one you've been living with. One overlooked possibility may be the way the driveshaft itself is assembled. The yokes have to be aligned correctly with respect to each other. I believe it's called phasing. If not configured correctly you will get vibration. No, I've never experienced the problem myself, I've just read of it.

 

[joecdeere]

Most Kubota shafts have a master spline to prevent that, my bet is the
shafts have worn where they slide into each other allowing the shaft to shake. I had a F-2000 and it did that too. Grasp the shaft in the middle and see how much it gives up and down

 

[Capt.Ron]

It's unclear whether this is a new problem or one you've been living with. One overlooked possibility may be the way the driveshaft itself is assembled. The yokes have to be aligned correctly with respect to each other. I believe it's called phasing. If not configured correctly you will get vibration. No, I've never experienced the problem myself, I've just read of it.

It's been an issue for about 1 year but has progressively gotten worse. As JoeCdeere said, it has a master spline that forces the proper alignment. After further inspection, I did notice that there is now some play in one of the Ujoints. There was no noticeable play a few weeks ago.
Now it's got me wondering, was it the Ujoints all along or are they just a victim of the vibration problem?

 

[Capt.Ron]

I noticed some slop in both yokes. The one at the tractor PTO and the one at the mower deck. I don't usually throw parts at a problem but I ordered new yokes and ujoints for both ends from Messicks.
They must be having a hard time finding them. It's been too weeks and I've received no notice of a delivery order being created. Hopefully they'll come through soon.
If that doesn't fix it, I'll open the gearbox to see what I find.

 

[Capt.Ron]

Bad news from Messicks. All of the parts for my PTO shaft are discontinued from Kubota.
One thought, the yoke at the gear box seems to have the most slop, if I could find the ujoints based on specs as opposed to mower and deck model maybe I can have the yoke bored and press a sleeve in so it will again be tight on the gearbox shaft.
Also, the gear box placement seems to ask for problems. It's offset from the shaft coming out of the tractor. I'm wondering if I were to rotate the gearbox a few degrees to at least make the gearbox shaft and the PTO shaft line up, would that help in reducing potential vibration once I get the rest repaired?

 

[RickB]

Having dissimilar angles on the two driveshaft u joints will increase the vibrations, not decrease them.

 

[Capt.Ron]

Having dissimilar angles on the two driveshaft u joints will increase the vibrations, not decrease them.

So you're saying that if I pivoted the gearbox so that the yoke and pto shaft were in a straight line that I would have more vibration because the other yoke isn't in a straight line as well?

 

[zzvyb6]

When the input and output shafts are CO-LINEAR (Don't have to be CO-AXIAL) then the U-joints need to be aligned with the yokes of the inner parts of the driveshaft at zero angle. Otherwise you need a phase angle to produce constant velocity. In this case (pto output and deck input), the input and output shafts are usually horizontal and point the same way from the top view, too, so NO phase angle.

 

[RickB]

So you're saying that if I pivoted the gearbox so that the yoke and pto shaft were in a straight line that I would have more vibration because the other yoke isn't in a straight line as well?

Correct.

Universal Joint Phasing | Belden Universal Joints

Phasing is the process of aligning the universal joint yokes on both ends of the drive shaft in a parallel fashion. Correct joint phasing is crucial for the assembly to operate at sustained velocity, without vibrations, in order to prevent sub-optimal operation and premature joint failure.

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