The differential pinion bearing failed, the cage broke and inner race spalled. Bearing in question inner race is the rotating race while the outer race is stationary.
The strange thing about this failure is that the inner race pitted for half of the circumference while the remaining half does not appear to be damaged at all.
The outer race is not damaged and appear to be in relatively good order. Crown wheel and pinion gear teeth and supporting bearings are in good condition and were not replaced.
The park brake disk and propshaft are mounted to this shaft and it is not clear why the failure only affected half of the inner race circumference.

Have anyone seen something similar. What might have caused this strange occurrence.

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Originally posted by Stefan Minnaar:
The differential pinion bearing failed, the cage broke and inner race spalled. Bearing in question inner race is the rotating race while the outer race is stationary.
The strange thing about this failure is that the inner race pitted for half of the circumference while the remaining half does not appear to be damaged at all.

The outer race is not damaged and appear to be in relatively good order. Crown wheel and pinion gear teeth and supporting bearings are in good condition and were not replaced.
The park brake disk and propshaft are mounted to this shaft and it is not clear why the failure only affected half of the inner race circumference.

Have anyone seen something similar. What might have caused this strange occurrence.

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Hi there,
I have seen similar failures on quite different machines so it's not something unique to differentials. I have always been amazed at how, sometimes, the other track can very little brinelling damage from the debris, and not have begun the fatigue cracking cycle as well.

How were the rollers ?
The cage breakage is right on the roller pocket corners and the cage is not distorted. Are there fatigue marks at these points ?
IT was a nice save, just the bearing damage, what was it that alerted you to the fault ?

Eccentricity of the bearing and gear is unlikely as it would show up while trying to adjust the crown wheel and pinion mesh and make a noise and tail shaft imbalance forces are minor compared to gear forces.

I suspect there is an initial failure due to slag inclusions etc on the inner race that starts if off, and the sub surface shear stresses just allow the surface to be sucessively cracked off around the circumterence. Just like a car hitting the trailing edge of a pot hole in the road.

The rough surface will vibrate the rollers which in turn vibrate the cage causing a fatigue failure of the cage.

Cheers

John

Hi John,

Thank you for the reply and there is a lot of merit to your comment.

The differential by nature of operation and construction transfer the lube from final drives to the the centre portion and vice-versa. There is a certain cavity in the differential housing construction where wear accummulate making it EXTREMELY difficult to flush (since been modified but not yet on this unit) and residual particles alway accummulate here. It is suspected that some of this particles / material might have entered the bearing initiating and propagating the wear.

We do 250 hr oil analysis on the differentials and detected a gradual increase in the analytical ferrous (Fe) level as well as the PQ value (relatively crude but terribly effective method for monitoring differentials). A descision was made to pull the unit based on numerous past successes and a sound reputation of the department as a result of "good calls".

Well the rest is history.

Have a great day!

The wear pattern observed on your inner race looks like the unit may have been subjected to vibration during a period when it was not operating causing false brinelling of the race which progressed to the point of failure. Vibration induced damage i fairly common and may be incured during transport if proper precautions are not taken. This problem may have been purchased with the unit.