What makes a tapered roller bearing get pitted?Pic

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Chris142

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My boss has a 40ft diesel pusher motorhome. He noticed a growl so he brought it to our shop today. I tore into it and found a dead wheel bearing on the right front.

This axle is the same as the ones on the 18 wheelers. The bearings are lubricated by 80w90 gear oil. It's a very HD setup.

Looks like the outer bearing started to come apart and when it contaminated the oil the inner bearing ate the contamination which damaged it too.

The coach only has 58K on it. Oil was full and other than the metal sparkles looked ok.

The semi trucks get hundreds of thousands of miles with this same setup. I'm wondering if they were too tight?

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My mess. This is how I spent my morning lol.

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Was there a seal leak which allowed the lube level to be too low, or was the seal compromised and let in dirt and mud?
 
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mostly due to dirt or moisture, improper installation/preload, inferior manufacturing, wrong type of grease (to a much lesser extent).

I bet ya Kesta can give better answer..

Q
 
Originally Posted By: MolaKule
Was there a seal leak which allowed the lube level to be too low, or was the seal compromised and let in dirt and mud?
The inner seal was fine. The outer was fine plus it has chrome covers that cover the hub so I don't see how dirt or water could have gotten in it.

No leaks and it's never been ran low on oil.
 
Can you get a better picture and show detail? What do the races look like?

Any corrosion present inside the bearing cavity?

For the rollers to spall in a taper bearing something horrible must've happened.

For now I'll say that most premature bearing damage comes from improper installation.
 
+1 to what Kesta requested (re: need clear picture).

Also a picture of the outer bearing race surface (please set your digital camera to take macro shots, focus better that way too).

Quest
 
Looks like preload or end float to me. Have seen quite a bit.

Just for grins, chek the brand of your bearing race and cone. They could be different. Sometimes on these truck axles the race is installed by the hub supplier and the cone by the vehicle or axle oem. Not uncommon in that type of application and occasionally problems such as your can happen due to such. Timken, SKF, or NTN usually will not warranty a mis match but the final assembler should.
 
Sorry. The only Camera I own is my little Cellphone and it's pics ain't the best.

The bearings and races are Timkin. Made in USA.

I cut the cage off the inner cone today. 1/2 of the inner cone is ruined. I can see where the rollers were when it got damaged.

Can moisture form inside the hub? Not boil off because the oil never got hot enough to boil it out?

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The damage is quite advanced. This is called a "load zone spall", which you probably already know intuitively.

Moisture would result in a characteristically shiny raceway. I don't see that in the picture, or any other evidence of moisture damage.

The roller spacing in the spalling suggests the bearing may have been brinelled... either hammered on, or a hard hit on a curb. Brinelling can easily lead to spalling.

The damage seems even across the width of the race and rollers. This suggests the bearing did not go into clearance.

It's a good bet that the bearing preload was too tight (negative clearance). So you initial gut reaction is likely correct. Check the large end of the rollers and mating guiding flange surface. You may see wear on those surfaces. Who installed these bearings?

I still need more resolution to make a better diagnosis.

As a side note, this is one of the reasons the bearing industry has moved from serviceable double tapers to self-contained hub units that came preloaded from the factory. It reduces mistakes made during installation or servicing. There were too many clients with damaged bearings claiming "bad bearing" when it was really "mechanic error".
 
Would the fact that this was the right side of the coach mean anything? I assume that this side gets more bumps such as hitting curbs and potholes?

Could a good hit start the damage and as the bearing rolled around it just go worse everytime it went over the damaged spot?
 
Originally Posted By: Kestas
Who installed these bearings?

These are the original bearings. This was the 1st time that the front end has been apart. I believe it's a Rockwell axle just like the one in my Peterbilt.
 
Originally Posted By: Chris142
Could a good hit start the damage and as the bearing rolled around it just go worse everytime it went over the damaged spot?

Yes.
 
Originally Posted By: Kestas
Originally Posted By: Chris142
Could a good hit start the damage and as the bearing rolled around it just go worse everytime it went over the damaged spot?

Yes.
good! Job security for me
lol.gif
My boss can just keep hitting stuff.
 
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