Front tires caused axle failure...?

[dieselscout80]

I bought a used Kubota m5400 earlier this year. The previous owner had put some 15x19.5 loader wheels and tires in the front. Replacing the original 9.5x22s. it was really nice to have such a wide front tire, for loader work and wet ground.

I double checked online, and the rolling circumference of the original tires was listed as 117". The 15x19.5s was either 118 or 120" depending on which website you believe.

Well not long after I ground up the right side hub and bevel gears, bearings, etc. Parts alone...$3,600!!!!

So now I'm thinking it must have been the tires. But was it? Maybe it was more the width of the tire as opposed to the circumference? Or maybe just the weight? These wheels and tires weight like 150# each.

Anyways I'm not going to leave it in 4x4 anymore, only when it's really needed.

But before I get a new set of front rubber for the old, narrow wheels, I wanted to make sure with the group it was the necessary move.

Thanks

How did the previous owner use it?

It may have to do solely with how that person used it tractors with loaders are not bulldozer, but are sometimes used like it with failed components as a result.

 

[crazyal]

How did the previous owner use it?

It may have to do solely with how that person used it tractors with loaders are not bulldozer, but are sometimes used like it with failed components as a result.

That's the rub. Did the PO let the oil level get too low and then just filled it up? Did the PO use the loader a lot and/ or drive it in 4wd on pavement? Without answers to these kids of questions debating if incorrect tire size was the cause is pointless. I had a bearing go on my dozer for the rear drive sprocket. It happened in the middle of a muddy field with no way to get it out without driving it. Being as careful as I was it still tore up the gears pretty badly. The oil level was fine. The bearing was at the end of it's life. Things do fail. If you are worried about the other side I would jack up the front to see if there's any play in the axle or an unusual noise. You still could replace the bearings on the other side before one fails. 3000 hours is starting to get up there.

 

[rScotty]

I would not leave your tractor in 4wd all the time no matter what. The reason is because it creates a lot of stress in the driveline every time you turn.
When the 4wd is locked in and you turn, the front wheels are traveling different distances in the turn from each other and different than the rears, so you create bind all the time. When you have a loaded bucket and you are turning in 4wd, you are really stressing the system. Plus you can wear the tires a lot faster.
I am not saying that leaving it in 4wd is what caused your trouble, but it didn't help. I would guess having those wide tires stuck all the way out probably stressed the bearings and one thing led to another. Based on what you said your circumference numbers were, I wouldn't think you would be introducing so much lead that you would break the driveline.

For what its worth, I don't ever use my 4wd unless I need it, and then I lock it in and as soon as I don't need, I unlock it. Actually, for what I do, I seldom need it.

That's how I do it as well. Even if the tires are perfect and the ratio is too, there is still drivetrain stress in 4wd just because that lead/lag is a slight positive ratio rather than being zero.

Any load in the FEL bucket makes this worse and that wear just keeps getting built up and multiplied on high traction surfaces. Pavement is a high traction surface because of friction, black top even more so. But we've all seen high traction mud or even deep snow.

Tractors have 4wd assist; it isn't automotive type full-time 4wd. The 4wd design most tractors use has some serious compromises because it lacks a center differential. Basically it is there for when you need it. It wasn't designed to be used all the time. The less 4wd is used, the longer it will last.
rScotty

 

[5030]

Exactly Scotty. Een in an automotive situation, continuous use of all wheel drive in a not needed situation accelerates tire wear, suspension and drivetrain stress and reduced fuel mileage. Why AWD vehicles have a selector to disengage the front (or rear) differential and driveline.

 

[Diggin It]

I'm never in 4W and Hi ... always Lo. And I don't try to run fast, mostly due to my hills and rough ground. When I have to cross my blacktop driveway, I creep and try not to turn any more than I have to.

 

[Oldpath05]

All you guys that hardly ever use four wheel drive makes me wonder why you even have a 4 wheel drive tractor to begin with. Me, I hardly ever use 2 wheel drive, it's in 4 wheel most of the time and lots of times I'm in diff lock. very few times I get on a hard packed flat road. To me it's just turning gears in oil, the rear end has tuning gears in oil, the front end has tuning gears in oil, all the gears are in oil and turning.

2nd thing is, sub compacts like mine have open differentials front and rear, no limited slip like pickup trucks so there is no wheel hop in turning corners so at best I have 3 wheel drive, but it is important put the right size tires on a 4x4 tractor. Gears in oil with right size tires shouldn't break, if they do it's a design flaw but gears in oil do ware in time. Strange there are still 70 year tractor with gears in oil still going.

 

[rScotty]

I'm not sure we are talking about the same thing. The problem with tractors in 4wd is that tractors don't have a center differential in the shaft that connects the front and rear axles. If they did have that extra third differential, that would allow the front and rear driveshafts to turn at different rates.

As is, the the front and rear driveshafts are locked together by whatever the pre-set ratio is in the transmission, front and rear diffs, and tire size. So the only way to take the stress off the drivetrain is when a tire slips on the ground. If you normally operate in 4wd without problems that's probably what is happening.... the tire can slip if it needs to. If that can happen - and the design is good - then the main thing that you will see is early wear on the front driveshaft U joints.
rScotty

 

[thoner7]

Well I reached out to Kubota corporate, and they weren't helpful at all.

Unfortunately the safe thing to do is go back to stock, which will make my loader useless for half the year, because of the narrow tire width.

 

[Oldpath05]

What kind of help did you ask for, they should've given you tire size specs with tire options.

 

[MHarryE]

Did they start leaking oil before the catastrophic failure? When my L5740 started leaking oil onto the inside of the rims, I checked here and found it not unusual when doing a lot of loader work like load and carry. As I caught it early, no damage other than failed bearings. My dealer said he has one customer who brings the drives into the dealership as they fail (yes, it is that frequent). They replace the bearings, he reinstalls and goes on.

The axle shaft is like a lever working on the bearings. If the center of the wheel is over the midpoint of the bearings, the bearings are loaded equally. Widen the tire and that load line moves away from the midpoint. If it’s outside the outer bearing, the outer bearing is handling all the load designed to be carried by 2 bearings. Move the load point out further and the outer bearing is loaded even more than the weight carried by the wheel due to leverage. Bearing life is a factor of the cube of the load so just a little shift causes a large reduction in bearing life.

Your tire radius difference is insignificant. Your tire width is very significant. But the tractor went 3600 hours before failure. I do realize that part of those hours were with the standard size. If you replace the bearings before they fail to the point that they damage the gear, you can keep using the wide tires. Kubota uses that style final drive on the front in order to get a tight turn radius. My M7 has much wider fronts than the drive tires on my L5740. To make it work the M7 has a different style final drive - a planetary - and the turn radius is a country mile. But it can withstand the load. However it is not robust enough to use duals on the front like you see on so many over 250 HP tractors.

The following is an excerpt from diagnosing failures like yours:


Increased Offset – Most oversize tires are on wheels that are offset so the tires don’t rub. This moves the load on the bearing to the outside, so the load on the bearing is no longer centered.
Increased Leverage – A larger tire is a longer lever. A heavier tire puts more force on the lever. A long lever with more force behind it puts greatly increased leverage on the bearing and hub.