BX23 Ujoint / new vibration question

[Ex Five 0]

Hello to all tractoring dudes. I am reaching out to our collective knowledge base to get some answers regarding a repair/operation issue involving my 12 year old 800 hour BX23 TLB.

Sorry for the long story, but I wanted to include as much background data as possible.

The slope of my property requires 4WD use for most areas. Towards the end of last summer, while mowing with a 48 landpride rear mower, I noticed that I had lost drive to my front wheels. A look under the tractor immediately disclosed that I had lost middle Ujoint for the front drive shaft. I backtracked the area that I had mowed but was unable to recover the lost part. I ordered a replacement ujoint assembly and roll pin and completed the simple repair.

The next time I mowed, I noticed a vibration when the 4WD was engaged. Since I had also recently replaced the front tires, I chalked up the vibration to the tread on the new tires (the old set were essentially baloney skins)

Now, I am noticing that what I thought was tire tread vibration, is in fact only present when 4wd is engaged. I did a test by putting the tractor up on stands and testing for the vibration by running in 2wd and 4wd. The test confirms the source of the vibration is somewhere in the front wheel drivetrain.
I have also found the lost ujoint and have attached several pics of its condition when it was found. Note that there is a portion of the roll pin still in place.

So I have 2 questions:
1) How is it possible to shear off the roll pin without damaging the Ujoint splining.
2) What sort of damage also occurred to the front drive train during the ujoint event that has led to the vibration?

I would luv to hear your thoughts, suggestions and advice.
Brian

 

[Henro]

When you install a u-joint it must be "timed" to match the other u-joint. Maybe you got it wrong. If wrong there will be vibration. Timed means the physical relationship between the two u-joints is important.

I lost a U-joint on my bx2200 last summer. Same issue, the roll pin sheared off after about 1200 hours. It happens. Not sure why...

Do an on line search for u-joint timing, or something similar. This may give you the answer...

Edit: after buying and installing a new u-joint, I found my old one on the top of the mower deck. So I have a used but still apparently good spare now...

 

[Dave_eng]

If a pto shaft cannot telescope easily, the forces can shear off a roll pin. The roll pin is not failing from a rotational force otherwise the splines will also be damaged.

Modern pto shafts are designed so they cannot be assembled "out of phase." Perhaps by having a space where there is no spine or by the shape of the male and female halves of the shaft

Dave

 

[Henro]

Modern pto shafts are designed so they cannot be assembled "out of phase." Perhaps by having a space where there is no spine or by the shape of the male and female halves of the shaft

Dave

Dave,

That may be the case with PTO shafts but it is not the case with the front drive shaft on a BX Kubota. At least not on mine.

There is only one hole in the shaft that the u-joint attaches to using the roll pin, and multiple spline positions where the shaft goes in the other end of the u-joint. Without proper care the odds are probably 10 to 1 it will be installed out of phase to some degree.

I only know because I went through the same issue with my BX2200...but did not suffer a vibration problem because I knew the importance of u-joint orientation.

 

[Dave_eng]

Dave,

That may be the case with PTO shafts but it is not the case with the front drive shaft on a BX Kubota. At least not on mine.

There is only one hole in the shaft that the u-joint attaches to using the roll pin, and multiple spline positions where the shaft goes in the other end of the u-joint. Without proper care the odds are probably 10 to 1 it will be installed out of phase to some degree.

I only know because I went through the same issue with my BX2200...but did not suffer a vibration problem because I knew the importance of u-joint orientation.

Glad to discuss further with you.

To be clear that we are talking about the same two joints where phasing is important, I have attached a marked up photo. The two yellow arrows are the U joints which must be in phase. The other halves of those joints can connect to shafts at any angle

It seems quite improbable that Kubota's designers would use a design which could permit incorrect assembly right from the factory. Assuming the roll pin is the only component transmitting shaft torque, all that would have to be done as a design would be to drill the hole for the roll pin slightly off center and then the parts could only go together one way.

Dave

 

[Henro]

Dave,

I do not know what that drive shaft is from, and I do not doubt it may be splined in a way that prevents assembly other that in one orientation.

My recollection is that the front drive shaft on the BX Kubota has splines evenly spaced, and actually can be installed in multiple orientations, when inserted in to the U-joint.

I am familiar with the type of splined shaft that has one flat spline on it, that ensures it can only be assembled one way. I do not recall that being the case with the BX Kubota front drive shaft in my case. I did spend time making sure I got the orientation right when I replaced mine. Would not have had to worry about it if it could have only gone together one way.

Since the OP has a vibration problem after replacing the lost U-joint, and may not have paid particular attention to the time between the two u-joints, it seems likely he may have assembled it out of phase.

But I have a BX2200, and his is a later model.

Perhaps someone that knows for sure can add something.

But in my case there is absolutely no question that, had I not been careful, I could have installed the replacement U-joint on my BX out of phase.

Edit: The roll pin does not transmit torque, it simply holds the u-joint in position on the shaft. The splines on the shaft transmit the torque. The other end of the u-joint is free and slides on the shaft. This is on the transmission end. I do not recall if the axle end had one roll pin or two.