Front wheel bearings failed L5740

[MHarryE]

Calculating the bearing life is not so simple as looking at the basic load rating. Part of the life equation (revolutions) is a factor of (dynamic load rating/equivalent load)cubed. If the bearing load is the rated dynamic load, this factor is simple - one. If the bearing load is one half of the rated load the life will be 2 cubed or 8 times longer than if running at rated load. Now drive on a side slope and thrust load is added and these bearings are not designed for high thrust loads. Life calculations get very complicated as an example I had the load histogram taken from field test data for a drive. Bearing life was the critical parameter. I gave the histogram data in percentage time at given loads having broke my data into 30 different load ranges. When looking at the computer generated results, only the 3 highest loads were significant. Combined they represented only 5% of the operating life but that cube factor becomes so significant. Yes I run my tractor hard. Bearing life was a concern do I routinely loosed for leaks. I had hoped for better but I am not extremely disappointed with my bearing failure.

 

[Complete Turf Care]

I spent all day loading big rolls of sod into the planter. I estimate these rolls weigh about 1000-1200 lbs each. Hopefully, I didn't break any more bearings.

I did seem to feel a 'chatter' from time to time. I'm thinking that may be the gears that were chewed up pretty good on the first side that I changed.

Well, more work for the tractor today.....I hope it holds up.

 

[SPYDERLK]

I spent all day loading big rolls of sod into the planter. I estimate these rolls weigh about 1000-1200 lbs each. Hopefully, I didn't break any more bearings.

I did seem to feel a 'chatter' from time to time. I'm thinking that may be the gears that were chewed up pretty good on the first side that I changed.

Well, more work for the tractor today.....I hope it holds up.

View attachment 430516

The gears will be fine. ... Just raise the fronts and feel for play occasionally. You dont want any more bearing parts running around loose in there.

 

[rbargeron]

I'd like to offer the group a different mental image of what's going on in a ball bearing - and how failure starts.

Imagine rolling a bowling ball along on top of a bed. After one run, there isn't much evidence of the ball rolling across it. But after many back and forth trips of the ball, the sheets and other coverings get stretched a bit, the top internal layers of the mattress become frayed.

In a ball bearing the same thing is going on - the bearing surfaces are hardened so the deformation is tiny, but it's real. In the grains a few layers below the surface the shear displacement can be significant. The accumulated damage can get to where the ball or the race develops lateral cracks, and microscopic chunks of material break out. After enough of that goes on the bearing gets rough and noisy and eventually may shatter.

The biggest single factor in a bearing's life is how many internal metallurgical defects it has from new. The mean time to failure at "rated load" may be few million cycles, but the standard deviation is large. Sometimes a visually perfect looking bearing has an internal flaw and fails very soon, even at low load. But the average life of the whole bearing population is very long so it's considered an acceptable situation, given the cost of a major redesign of the manufacturing process or a costly inspection program to examine each one made.

Many machines use tapered roller bearings instead of the ball type. Rollers have line contact instead of point contact so the stress is distributed and lower. Car manufacturers switched to tapered roller wheel bearings 65+ years ago when new cars shipped by rail were arriving at dealers with failed ball bearings (from the constant hammering of rail splices). But tractors haven't followed their lead. Kub uses ball bearings extensively and has apparently never seen fit to change.

All of this said, my bet is that for every tractor with a failed wheel bearing there are many hundreds that are fine, even those lifting big loads.

 

[David Devuono]

From many many years of off-roading where water\mud is what we went looking for, I have had a few bearings go out in my days. They always gave plenty of warning. It might be in a large tractor that you have to use a pry bar and dial indicator to see that wear. I know on my B3200 I surely would never hear nothing till it broke due to the HST wine. If those bearings were wearing out, they would have caused some play and took out the oil seal before a major failure. I am guessing its a stress failure. From what I read, a Sod bale is likely less than 1,000 lbs so should not be a workout for your tractor. Also from off-roading experience, we knew that by going with a wider rim that pushes the tire out, you put more stress on the wheel bearings. If I was paying for the repairs, I would not do this work in the future without a verified 1500 lb counterweight. (I am scared now and going to add concrete to my counter weight)

With respect to the chipped ring gear, it will shed metal bits at an excelerated rate. I would try and get a super magnet or two installed to hold some of that metal. Maybe stick one to the drain plug?

 

[MHarryE]

When you said car manufacturers switched to tapered rollers and tractors never followed their lead I was surprised. The first front wheel drive cars in America switched back to ball bearings. I checked and verified - the most popular car in America today, the Toyota Camry, uses a double row ball bearing for the front wheels.

I won't dispute that in general, tapered rollers have longer life, but they have limitations such as speed. Unlike a true spherical roller, they have slippage and generate heat. High speeds and tapered rollers do not mix. Wheel bearings, however, are not high speed.

So it comes down to packaging. Ball bearings do not require precise clearance or preload (depending on load) like taper rollers. They run cooler so lubrication is not as critical - lubricant deterioration.

So our 60 year old Farmalls have tapered rollers and fail if overloaded or not properly serviced. I assume Kubota had a reason for selecting ball bearings (any bearing supplier or bearing design handbook will guide a person through the selection process). Being Japanese, however, they may not realize how North Americans treat their equipment. My experience in Japan, though limited, found very focused operators. They do not tend to use machines to the limits. Can this result in under-designed designs? One would think with all their North American experience they would have learned by now many North Americans use their machine to 110% of its limit.

 

[rbargeron]

........The first front wheel drive cars in America switched back to ball bearings.......

Always nice to read your informed posts Michael. You may be retired but you're not a "former" engineer, you still have an active practice! As often happens I posted a comment without acknowledgment of contrary facts. Bearings are a big subject - maybe several library shelves (or servers). Mostly I was trying to get people away from thinking the first time they lift something heavy their bearings will fail. Years ago I looked into Hertz contact stresses for crane rails & wheels that see 250,000 psi. Failure starts well below the surface - similar situation with rolling bearings. Take care, Dick B.

 

[Complete Turf Care]

Well, it's been just over 3 years, and it happened again today. Right front wheel fell off. Bearings are gone. I guess I am putting too much weight on the front with the loader.

 

[MHarryE]

Well, it's been just over 3 years, and it happened again today. Right front wheel fell off. Bearings are gone. I guess I am putting too much weight on the front with the loader.

Not too much load, too much load for long bearing life. Reducing the load will increase bearing life, but a person could weigh replacing bearings every 3 years versus carrying half bucket loads. Fortunately the bearing is an easy job for do it yourselfers. My dealer told me he has a customer hauls in the front drive assemblies every 2 years and has them rebuilt. Uses his Grand L in a low clearance building to clean manure and feed large bales.

 

[Complete Turf Care]

Ordered the parts today from Messicks. About $575 for everything. The most expensive part is the bevel gear at about $280 and the 'axle' is about $150. My wife works at a local tractor dealer (not a Kubota dealer) and that's where it is being repaired.

Last time this happened, the opposite side went out a week after the first one. I'm hoping this doesn't happen again.