B26 repair of broken u-joint on front drive shaft at HST output

[rScotty]

Good on you for even thinking of doing the repair yourself. You seem like a logical guy so I can't think of any reason you could not do it as well as the Kubota shop. Hopefully it is just unbolting, pulling apart, pressing pins, and rebolting. There shouldn't be any machine work, pressure, or special measurements required. I would research it more before cutting for access....

If you go for it, just go slow and keep parts in separate baggies and in order. Take pictures & notes.

Doing any new job like this, I have always found a parts book with good exploded artistic illustrations to be much more helpful than the shop manual.
There are some good shop manuals out there, but even with those I find it is the exploded diagrams that help more than the text.

How is the U-joint affixed at both ends? Splines? Pins? Bolts?

BTW, what do you think caused the failure? Normal cause of this type of U-joint failure is drive shaft "windup" due to being in 4WD with heav loads on high traction surfaces.
A symtom that the shaft is getting too much windup is if the tractor is difficult to shift OUT of 4wd.

The complexity you are showing makes a strong case for the alternate design used on older 4wd compacts pre-2000 or so. On those, the front shaft was a splined 2 piece shaft inside a telescoping dust cover. Very accessible, although some did require loosening the front axle & sliding it forward - but that is easily done. With that type design, front shaft U joint repair was an afternoon job.
Good luck, I'll enjoy following along.
rScotty

 

[SamWalton]

Does the driveshaft have a slip joint to allow for suspension travel?

I don't think. It looks to be a fixed measurement between shafts. The second u-joint is fixed through the bell housing.

 

[SamWalton]

Good on you for even thinking of doing the repair yourself. You seem like a logical guy so I can't think of any reason you could not do it as well as the Kubota shop. Hopefully it is just unbolting, pulling apart, pressing pins, and rebolting. There shouldn't be any machine work, pressure, or special measurements required. I would research it more before cutting for access....

If you go for it, just go slow and keep parts in separate baggies and in order. Take pictures & notes.

Doing any new job like this, I have always found a parts book with good exploded artistic illustrations to be much more helpful than the shop manual.
There are some good shop manuals out there, but even with those I find it is the exploded diagrams that help more than the text.

How is the U-joint affixed at both ends? Splines? Pins? Bolts?

BTW, what do you think caused the failure? Normal cause of this type of U-joint failure is drive shaft "windup" due to being in 4WD with heav loads on high traction surfaces.
A symtom that the shaft is getting too much windup is if the tractor is difficult to shift OUT of 4wd.

The complexity you are showing makes a strong case for the alternate design used on older 4wd compacts pre-2000 or so. On those, the front shaft was a splined 2 piece shaft inside a telescoping dust cover. Very accessible, although some did require loosening the front axle & sliding it forward - but that is easily done. With that type design, front shaft U joint repair was an afternoon job.
Good luck, I'll enjoy following along.
rScotty

Thanks for you help. I did purchase the PDF shop service manual which provided many new pictures which have clarified many things. I posted some of these screen shots. What I have learned is the drive section I need to repair is in a fixed distance design. Previous I thought I could detach the second u-joint but it actually goes through the bell housing.

One consideration, which is a long shot would be if all u-joint pins were removed on both sides at the HST and also the pin holding the drive shaft at the second u-joint. It may be possible to break down the replacement u-joint and insert the drive shaft into all required yokes and push them past the pin positions as to provide enough room to reseat the replacement u-joint into it's seats and replace the bolts and holding collars. The real question on this possible solution is how much room can be gained if the three shaft to yoke connections are pushed beyond it's pinned locations?

Because the u-joint is broken I am able to slide the drive shaft almost completely out of the front u-joint at the bell housing.

A second possible solution is to machine and weld in some sort of telescoping coupling to allow clearance to complete the repair.

 

[SamWalton]

I have been told by Kubota the service to replacement this u-joint will cost at minimum $1100. They have never done this repair to a B26. I purchased the PDF service manual and learned what i could. I previously removed the hydraulic tank and was able to remove the parts after removing the stopper bolt. The remaining half of the u-joint is still on the shaft of the HST. This stopper bolt retains the bearing and u-joint which is pressed into the bearing and also the plastic cover. While handling the parts I noticed the spline shafts can penetrate beyond the pinned locations providing what may be enough room to do the repair without the damaging tear down. I will open the bottom plate to complete the repair. If necessary I will have the shaft made to be collapsible with lockability at full extension.

 

[rScotty]

Sam, I've been studying the pictures you've posted and am kind of confused. Is there some sort of intermediate gear box between the HST and front axle? It almost looks as though the front driveshaft is offset laterally from the front axle pivot point.... but that doesn't make mechanical sense at all for a U-joint design.

So I'm confused. Can you help with a real basic tutorial on the way the B26 is set up? Is that center case or whatever it is even necessary for your application?

Here is a diagram of the way the M59 front axle is driven. The transmission output and the front axle input are on the same centerline and rigidly held. There are no U joints.
However, take a look at the couplers # 020 & 030. They are capable of handling twice the horsepower of the B26, and best of all are already machined. It might be easier to make external splines to match than to try to machine a coupler. Or maybe find an imperial dimension equivalent.
rScotty

 

[SamWalton]

Sam, I've been studying the pictures you've posted and am kind of confused. Is there some sort of intermediate gear box between the HST and front axle? It almost looks as though the front driveshaft is offset laterally from the front axle pivot point.... but that doesn't make mechanical sense at all for a U-joint design.

So I'm confused. Can you help with a real basic tutorial on the way the B26 is set up? Is that center case or whatever it is even necessary for your application?

Here is a diagram of the way the M59 front axle is driven. The transmission output and the front axle input are on the same centerline and rigidly held. There are no U joints.
However, take a look at the couplers # 020 & 030. They are capable of handling twice the horsepower of the B26, and best of all are already machined. It might be easier to make external splines to match than to try to machine a coupler. Or maybe find an imperial dimension equivalent.
rScotty

The B26 design uses two spline shafts and two fixed offset u-joints. The front axel pivots at the center of this drive shaft. The U-joint at the bell housing has a pressed baring which hold everything with the stopper bolt.

View attachment 690869View attachment 690869

 

[Username Taken]

Looks like you're gonna be okay.

One word, I don't know much about Kubota but I can tell you that when we had the same (similar) problem on our JD 2305, the broken U-Joint beat the snot out of the yoke and damaged it badly. To the point it looked really weak. Mostly because -- It was.

I thought, "No problem, those splined yokes are a dime a dozen."

Not. JD uses a proprietary spline. No other spline will fit. The Driveshaft cost $800 and we were lucky to find one. Couldn't find a junk shaft to cut the splined ends (yoke) off of. No way.

Make sure Kubota isn't doing the same thing. Make sure (if you need new splined ends) that standard will fit before you get too involved.

We took days and days tearing that POS apart and when I discovered the price of the driveshaft, welded it up and put it all back together. Held up until it got sold. Told the buyer the whole story beforehand. He didn't care.

JD can forever and always kiss my goat-smelling butt over that. It's okay to make proprietary fittings and parts but make sure they're available and don't rip people's heads off when they need them. Sears did that. They'd have somebody like Whirpool make their appliances but make them design-in proprietary replacement parts available only at Sears. I stay away from those kind of people if at all possible. They even did it with toilets. I know.

I would hope Kubota has more class than that

 

[dfkrug]

The Driveshaft cost $800 and we were lucky to find one. Couldn't find a junk shaft to cut the splined ends (yoke) off of.

Yeah, I hate that. But I also try to work around it with substitutions and custom machine work. A machine shop can cut splines on a shaft or broach female splines.

JD is the worst I have run into, tho there are some seriously spendy OEM Kubota parts. I remember finding a substitute tie rod end for a JD 4300 that I still had to customize to fit. I am currently fabbing up a small hyd cyl that Ditch Witch prices at $700. Nuts.

 

[SamWalton]

Looks like you're gonna be okay.

One word, I don't know much about Kubota but I can tell you that when we had the same (similar) problem on our JD 2305, the broken U-Joint beat the snot out of the yoke and damaged it badly. To the point it looked really weak. Mostly because -- It was.

I thought, "No problem, those splined yokes are a dime a dozen."

Not. JD uses a proprietary spline. No other spline will fit. The Driveshaft cost $800 and we were lucky to find one. Couldn't find a junk shaft to cut the splined ends (yoke) off of. No way.

Make sure Kubota isn't doing the same thing. Make sure (if you need new splined ends) that standard will fit before you get too involved.

We took days and days tearing that POS apart and when I discovered the price of the driveshaft, welded it up and put it all back together. Held up until it got sold. Told the buyer the whole story beforehand. He didn't care.

JD can forever and always kiss my goat-smelling butt over that. It's okay to make proprietary fittings and parts but make sure they're available and don't rip people's heads off when they need them. Sears did that. They'd have somebody like Whirpool make their appliances but make them design-in proprietary replacement parts available only at Sears. I stay away from those kind of people if at all possible. They even did it with toilets. I know.

I would hope Kubota has more class than that

"Make sure Kubota isn't doing the same thing. Make sure (if you need new splined ends) that standard will fit before you get too involved."
Great point, I plane on trying to install the stock parts hopping the spline over shoot will allow assembly. If it is not possible I will simply try other simple adaptations.

 

[SamWalton]

I purchased a Plasma Cutter (Tosense CUT50P 50A Non-Touch). Not pretty on my first try but did the job. Gained access and was able to learn I need basically an extra half inch to allow the u-joint installation. I am hoping to get the drive shaft shop to move the spline and stop to allow an additional half inch of penetration.