What's all this fuss about transaxle bearing loads?

[wallfish 15,951]

Yeah, the weakness in the axle was right at the key way. Running 10.5 duals  put a huge amount of leverage force on those axles. It was just way too much with those wide tires. I also had the air pressure in the outside tires too high. Running low air pressure in them will not transfer as much force to the axle but that's something I discovered too late.

 

The ground was not completely level and I was actually using the tractor to level the backyard and spreading about 20 yards of dirt at the time.

 

COMPLETE failure of the axle occurred. Still have the trans here somewhere, maybe I can get a pic of the broken axle

 

I agree with Sparky, adding the weight to the rim and/or tires is a much better choice overall

[DennisThornton 4,769]

I've only read about broken axles and even the cast iron axle projections on the trans case so I'm quite curious about the cause.  I've gathered that duals increase the risk and I can understand why the increased leverage could break either the axle or the case, so I like Craig, would like to know if uneven ground is the issue and could duals be used safely on flat terrain.  I'm thinking that uneven ground putting all the weight on just one outside wheel is most likely the case.

 

But what else breaks axles and cast trans housings?

I've only read about broken axles and even the cast iron axle projections on the trans case so I'm quite curious about the cause.  I've gathered that duals increase the risk and I can understand why the increased leverage could break either the axle or the case, so I like Craig, would like to know if uneven ground is the issue and could duals be used safely on flat terrain.  I'm thinking that uneven ground putting all the weight on just one outside wheel is most likely the case.

 

But what else breaks axles and cast trans housings?

[DennisThornton 4,769]

12 minutes ago, WNYPCRepair said:

 

 

Completely agree. I've always thought that thin bar of steel from the hitch pressing (bouncing) into the transaxle was a bad design

 

I've never thought of that "thin bar of steel" as anything more than just a tow bar that could handle only a nominal tongue weight, something someone could easily lift and lower like a cart or better yet a wagon.  I can't remember any WH brochure showing it carrying just weight, though I could have not only overlooked it but also forgotten.  My memory is NOT improving!  And Brian, speaking of which, did you get a TORO weight box with either of your 5XXxis?  They use not only the tow bar hitch but also really tie into the frame.  Obviously TORO didn't mean for the tow bar to take all that weight!

[wallfish 15,951]

I think you can safely run dual tires with just a few things to keep in mind.

Slide the hubs as far in towards the case as possible without touching the seal to put less stress at the key way

Use low air pressure in the outside tires and maybe even higher than normal pressure for the inside tires

Don't double up those extra wide 10.5 tires

and the rougher the terrain, the better the chance of breaking something.

[DennisThornton 4,769]

27 minutes ago, wallfish said:

Yeah, the weakness in the axle was right at the key way. Running 10.5 duals  put a huge amount of leverage force on those axles. It was just way too much with those wide tires. I also had the air pressure in the outside tires too high. Running low air pressure in them will not transfer as much force to the axle but that's something I discovered too late.

 

The ground was not completely level and I was actually using the tractor to level the backyard and spreading about 20 yards of dirt at the time.

 

COMPLETE failure of the axle occurred. Still have the trans here somewhere, maybe I can get a pic of the broken axle

 

I agree with Sparky, adding the weight to the rim and/or tires is a much better choice overall

 

That's seems to confirm what I've suspicioned.  A little less air pressure on the outside seems like a good idea too!

 

So what do you think now?  Are you or would you run duals again but with 8.5s or 9.5s?  Would you even try the 10.5s with less air pressure on the outside?  Maybe 10.5's inside and lower pressure smaller tires on the outside?  I remember seeing mismatched duals somewhere and thinking it looked odd, but maybe that was brilliance in disguise?  (Sadly, I don't always notice that...)

[WNYPCRepair 1,875]

9 minutes ago, DennisThornton said:

 

I've never thought of that "thin bar of steel" as anything more than just a tow bar that could handle only a nominal tongue weight, something someone could easily lift and lower like a cart or better yet a wagon.  I can't remember any WH brochure showing it carrying just weight, though I could have not only overlooked it but also forgotten.  My memory is NOT improving!  And Brian, speaking of which, did you get a TORO weight box with either of your 5XXxis?  They use not only the tow bar hitch but also really tie into the frame.  Obviously TORO didn't mean for the tow bar to take all that weight!

No, none of my tractors have any added weight other than wheel weights. 

Is there a reason they made the tow bar work like a hinge? I can't see any advantage to having the tongue move the slight amount it does, unless it is to prevent torque from the trailer tongue moving up and down over bumps, etc. from transferring to the mount point. And if that is the case, they should have spread it out over a wider area, or made some serious reinforcement to the transaxle case where it hits

 

[DennisThornton 4,769]

1 minute ago, WNYPCRepair said:

No, none of my tractors have any added weight other than wheel weights. 

Is there a reason they made the tow bar work like a hinge? I can't see any advantage to having the tongue move the slight amount it does, unless it is to prevent torque from the trailer tongue moving up and down over bumps, etc. from transferring to the mount point. And if that is the case, they should have spread it out over a wider area, or made some serious reinforcement to the transaxle case where it hits

 

 

Hard to believe that big snowblower worked well with no PS or rear weights!  Of course it could have had some but got removed.

 

No, I don't fully understand why the seemingly narrow hitch support nor why it swings some.  We'll have to wait for someone else to chime in...

 

However, the same supports for the tow hitch support the clevis and it certainly has to carry not only weight but also some jolts!

[WNYPCRepair 1,875]

3 minutes ago, DennisThornton said:

 

Hard to believe that big snowblower worked well with no PS or rear weights!  Of course it could have had some but got removed.

 

 

 

Well, I haven't had a chance to try it yet, so no idea how it works. Supposed to snow most of the week though, so maybe we will see. If I get off my rear and install the jack shaft and bearings

I do have about 240 lbs directly over the axle on the seat though    

[Don1977 604]

The main problem add weight add to the the tractor is wear on the axles, as the roller bearings run on the axles.

Edited January 10, 2016 by Don1977

[Ed Kennell 35,907]

2 hours ago, doc724 said:

I am pleased to see that this topic has prompted a lot of discussion.  Anyway, going back to Ed's question of yesterday about bearing life...I am not a bearing designer and going through the Torrington design catalog was enough to make my head spin...and I am too old for that.  What is significant is that since these are drawn cup bearings, there is no inner race, the needles contact the shaft directly.  The outer race is a thin steel shell which is a light press fit into the transaxle.  In order for the bearing to survive at all, the load cannot be supported by one needle.  Proper lubrication is needed to support the needle and distribute the load to the other adjacent needles.  Not any different than in a engine where the journal bearings support the crankshaft, but the crank actually rides on the thin film of oil between the crank and the bearing.  Lose the engine oil and you get a spun bearing (assuming the rings do not seize first).

 

There is not enough heat developed in a WH transaxle to cause the transaxle to seize, however, if you lose lubrication, the contact forces will be high enough to cause the needles to spall (fracture under a compressive load).  The seals in these machines were never designed for a 30 year life (or more in some cases).  All that is needed is a small breech and the gear oil will start to seep out.  Not enough to leave a spot on the floor, but as it gets hot, the viscosity goes down and more will seep out.  Pretty soon your transaxle is dry and from there everything goes down hill.

 

I am in agreement with Ed, (im)proper lube, not excess weight is likely the cause of any bearing failures.  That being said, others have raised very good points about too much weight on the rear hitch.  The local stress is very high where the hitch meets the transaxle.  It is a point (a line at best) and the contact area is miniscule.  Stress is simply load divided by the area (and don't forget the multiplication factor for the lever arms on the rear hitch).  

 

thx to all who have joined this lively discussion 

 

 

Great summary Don..... all good valid points.

[doc724 924]

Wallfish's description of the failure makes sense to me from an engineering perspective.  Without seeing the failure pix, I surmise that it was a failure in bending (not torsion).  Also, his description about letting air out of the outer tire makes perfect sense but not (directly) for the reason cited.

 

From an engineering analysis, think of the axle (half axle in this case) as a simple beam, supported on one end by the differential carrier bearing and the needle bearing somewhere in the middle.  The reaction force from the tire (actually half the weight of the tractor and all else on the rear) is cantilevered at the far end, centered approximately at the halfway point of the tire width.  When WH designed the axle this cantilevered dimension is in the order of maybe 8-10 inches (half the tire width, the length of the hub and on an 8 speed the space between the hub and the needle bearing).  If you put duals on and they are both equally inflated, the cantilever length is halfway between the two tires.  Since Wallfish told that he had the pressure in the outside tire cranked way up, I surmise that those tires were carrying all the load and the inner tires were not doing much at all.  So now the cantilever length is from the center of the outside tire to the needle bearing, maybe 2x what is was designed for.  Running on uneven terrain shifts the weight more to one side than the other, so not only is the cantilever length over the design limit, now the weight at the end of the cantilever is greater.  Add in the stress concentration (sharp edge) at the bottom of the woodruff key slot and you have the perfect storm so to speak.  Once the initial crack started at the bottom of the keyway,  everytime the axle would rotate, the crack would propagate (grow) a bit.  Eventually the axle will (and did) fail.

 

If this is what really happened, the conclusion to draw is that weight alone was not the culprit, but the LOCATION of the weight far out on the axle was the cause.   It is also possible that there was a lot of torque on the axle as a result of the big meaty tires.  If it was a torsion failure, the broken of the axle would have been a 45 degree stub.  Hard for me to think this was the cause as I would suspect that gear teeth or splines would fail, but these WH tractors when geared down can develop lots of torque (think of how many times you have lifted the front end when you popped the clutch).

 

 

 

[wallfish 15,951]

The outside tire pressure was not even "cranked way up", but they were probably filled with about the same air pressure as the inside tires, which I learned is way to high for that application during use on uneven terrain. When traveling over uneven terrain, the weight of the tractor could easily be transferred to the outer tire while the inside tire does not support anything. By keeping the outside tire basically "flat" with very low air pressure, the uneven terrain (within reason) will be absorbed by the tire flex while the stiffer inside tire with higher air pressure still carries the bulk of the weight. Something I mistakenly didn't consider when bolting on those extra tires. The reason for adding them at the time was to gain traction with a benefit of additional stability.

 

The axle was broke on an angle but my guess is it was probably caused more by the shape of the key way and not the torque spinning it. BUT, a combination of all is like you stated, "the perfect storm" and traction was definitely increased.

[JoeM 7,693]

Very good discussion on the bearings and axle strength.

I been running over 500 pound on my FEL for a couple years now. Worked the dog snot out her many times. About half the weight is on the wheels and the other half is in suitcase weight on the rear.

My yard is sloped and it makes for an interesting trip when I have a full bucket. The over hung suit case weights made the biggest difference on the hills. The wheel weights seem to add more tractive effort. No science, just seems that way. I know I started out with less weight on the wheels and the tractor had more zip. The heavier wheel weights seem to kill horse power.

The only axle issue was when I had a leaking seal. When I went to replace the seal,  found the hub was moving on the axle and wore the axle shaft enough that a new hub was to loose. Odd, the axle key was okay. I had a 1" hub bored out to  1 1/8" .002 under size at a local shop. It was tight enough that I had to heat it a little to in order to tap it on shaft.  

1 1/8" axle is a pretty stout axle size, the axles are slow speed and I figure they can good bit of abuse.

my thoughts and a buck 75 get a get you a coffee at Sheetz!

[Don1977 604]

On 1/17/2016 at 10:05 PM, oiluj52 said:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

i like your tiresVery good discussion on the bearings and axle strength.

I been running over 500 pound on my FEL for a couple years now. Worked the dog snot out her many times. About half the weight is on the wheels and the other half is in suitcase weight on the rear.

My yard is sloped and it makes for an interesting trip when I have a full bucket. The over hung suit case weights made the biggest difference on the hills. The wheel weights seem to add more tractive effort. No science, just seems that way. I know I started out with less weight on the wheels and the tractor had more zip. The heavier wheel weights seem to kill horse power.

The only axle issue was when I had a leaking seal. When I went to replace the seal,  found the hub was moving on the axle and wore the axle shaft enough that a new hub was to loose. Odd, the axle key was okay. I had a 1" hub bored out to  1 1/8" .002 under size at a local shop. It was tight enough that I had to heat it a little to in order to tap it on shaft.  

1 1/8" axle is a pretty stout axle size, the axles are slow speed and I figure they can good bit of abuse.

my thoughts and a buck 75 get a get you a coffee at Sheetz!

I like your tires. What size did you get?

 

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[JoeM 7,693]

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