Kubota HST Input Shaft Splines Stripped

Hysyde · Aug 2, 2020

While mowing with my old Kubota F2100 front mount mower the other day I came to a abrupt halt accompanied by a grinding noise. It didn't take long to figure out that the coupler coming from the engine/clutch was spinning on the input shaft for the HST.

Replacing the through bolt only got me so far (I snapped 3 to finish the yard) and I switched to a grade 10.9 (up from 8.8) which only got me so far as well.

I realize I brought this on myself as I use the tractor to pull heavy loads of wood out of the bush, and will often rock it back and forth when getting stuck in snow/mud ruts. Not what this tractor was designed for, but it's been a tough machine, taking this abuse for years.

I wondering what my options might be at this point. A look on the Kubota parts finder page puts this shaft at nearly $1200 which is a lot of money to invest in this old girl (about 3500hrs on the meter). Pluis this isn't a job I see doing myself. Pulling the HST doesn't look too bad, but I don't intent on splitting the case myself.

Could I have the shaft built up with weld and new splines machined?

What about welding the coupler right to the shaft, since it's ruined anyway?

Also, what is the purpose of the grease fitting for a coupler that doesn't move on account of the through bolt?

Any recommendations are appreciated.

5030 · Aug 2, 2020

Gonna go out on a limb and say the coupler (like the ones on mine are made of soft steel whereas the shaft is heat treated). I've replaced my couplers before, they cost 45 bucks each from the dealer and mine takes a roll pin, not a bolt. I believe they all take a roll pin from the factory, not a bolt.

Hysyde · Aug 2, 2020

5030 said:
Gonna go out on a limb and say the coupler (like the ones on mine are made of soft steel whereas the shaft is heat treated). I've replaced my couplers before, they cost 45 bucks each from the dealer and mine takes a roll pin, not a bolt. I believe they all take a roll pin from the factory, not a bolt.

Definitely a possibility and probably something I should try first, as it likely needs replacing either way.

I believe it's a bolt as the parts diagram show a bolt and locknut (and looking up the bolt it describes an M6 bolt).

Hysyde · Aug 2, 2020

I think I under stand the grease fitting now as it appears the coupler has a ball joint of some kind, I guess to accommodate whatever driveline flex there is.

5030 · Aug 2, 2020

Bet it's softer than the spline shaft, like mine is. Kubota isn't dumb about such items.

pmsmechanic · Aug 2, 2020

See if you can't find a browning taper lock hub assembly the same size and spline count as the input shaft. If so then take part #40 to a machine shop and have the hub welded on. Reattach to your input splines and tighten down the taper lock. Chances are it will never come loose again.

Actually a friend of mine did this on the splines of a hydraulic pump. He didn't even use a splined taper lock and the assembly held without slipping.

WranglerX · Aug 3, 2020

IT appears the the parts 40 and 50 are part of a CV joint.... IF you are blowing shear bolt/pin 100 then it may be easy to replace the CV joint and not have to deal with $1200 shaft....

Dale

Hysyde · Aug 16, 2020

I had "my guy" pull the HST and the shaft comes out relatively easy once you have the HST out. Both the shaft and the ball-joint coupler were demolished.

We talked about various options, many of which he was not comfortable with as he wanted to ensure it didn't end up with imbalance or vibration that could wreck (even more) very costly HST components.

Before I ordered a new shaft, he told me he was going to stop by a machine shop he deals with to see if they could re-spline the shaft. I'm guessing they were going to give it a shot, as I haven't got a call back.....

Hysyde · Aug 16, 2020

Again, I was disappointed that this shaft would have failed, then I remember how many times I had gotten bogged down in the mud and snow with a thousand pounds plus behind me. Nevermind the countless years of plowing abuse (II use a blower now on another tractor).

Industrial Toys · Aug 16, 2020

I'm shocked you get along with those turf tires in that terrain and envirnoment. Snow, maybe not so bad, but turfs and mud don't get along.

I had a pretty heavy duty Gravely walk behind. It too wore out the wheel hubs, that went on splined axle shafts. I guess castings are pretty soft by comparison to the hardened shaft.

radios1 · Aug 16, 2020

I can't imagine the shaft being $1200, that's crazy!. my friend had a dodge transaxle for a B body shortened to fit an A body, cutting the axle tubes, welding up, and cutting and re-splining the shafts costed $200.. btw, you are abusing the mower, it's not a tractor!..

4570Man · Aug 16, 2020

If they’re both steel I’d be inclined to weld it. But I wouldn’t doubt if the coupler is cast. Maybe you could drill the hole bigger and bolt it so the bolt isn’t as likely to shear.

5030 · Aug 16, 2020

Reminds me of the song, 'I fought the law and the law won. You abused it terribly so now you get to pay for the abuse.

Industrial Toys · Aug 16, 2020

The six inch or so one side of the axle, drive shaft in my E-Gator is about that much!

Hysyde · Aug 17, 2020

Industrial Toys said:
I'm shocked you get along with those turf tires in that terrain and envirnoment. Snow, maybe not so bad, but turfs and mud don't get along.

I had a pretty heavy duty Gravely walk behind. It too wore out the wheel hubs, that went on splined axle shafts. I guess castings are pretty soft by comparison to the hardened shaft.

4Wd, a diff lock, and occasionally chains on the front tires, really helps.

Hysyde · Aug 17, 2020

radios1 said:
I can't imagine the shaft being $1200, that's crazy!. my friend had a dodge transaxle for a B body shortened to fit an A body, cutting the axle tubes, welding up, and cutting and re-splining the shafts costed $200.. btw, you are abusing the mower, it's not a tractor!..

It's a fine line between working it and abusing it. Getting it stuck in the bush and rocking the hydro back and forth violently to get it out is abuse, but I wouldn't classify using it as a "tractor" as abuse necessarily. They're pretty robust machines.

I'm going to try to avoid using it as a skidder/bush machine, but the rear steering makes it agile through the trees. Much more so than my 1210 with a FEL on it and no power steering. More so than the ATV too. Looking at options for a "straight" pulling SCUT, but kind of hard to justify under the current circumstances.

Hysyde · Aug 17, 2020

4570Man said:
If they’re both steel I’d be inclined to weld it. But I wouldn’t doubt if the coupler is cast. Maybe you could drill the hole bigger and bolt it so the bolt isn’t as likely to shear.

Any bigger and I'd be worried about the shaft breaking. Not a lot of meat left if I did that.

pmsmechanic · Aug 17, 2020

Hysyde said:
It's a fine line between working it and abusing it. Getting it stuck in the bush and rocking the hydro back and forth violently to get it out is abuse, but I wouldn't classify using it as a "tractor" as abuse necessarily.

I wouldn't classify rocking the hydro back and forth as abuse to the input shaft of the hydro unit. The engine isn't changing rpm's and the shaft is running at a constant speed. The back and forth all takes place within the hydro unit. In this case the hydro isn't broken. The input shaft is.

ruffdog · Aug 17, 2020

A strong cheap fix may be to saw cut item 40 (flex joint) perpendicular to the cross bolt so it can be squeezed to the shaft. Then, use a clamp collar next to the bolt to squeeze the flex joint to the shaft. You would have to measure the OD where the cross bolt goes through. Here are the clamp collars:

McMaster-Carr