| Spindle failure evaluation [message #282948] |
Thu, 23 July 2015 13:39  |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma:
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Executive Summary: I believe it was a bearing failure.
The bearing were service about 18,000 miles and two years ago and the temperatures of brakes and bearings were checked at a stop in Hot Springs less than thirty miles before the incident.
Yesterday was a "recovery day", something I have not needed since the Mills Trophy Race of 2004.
The coach is outside our door and we are in the process of unloading it one handful at a time.
I am not done, but when I got to the Jenkins spare cover in the rear bedroom that is currently storing all the left over parts (we came home without a spare on the back) I looked in and the spindle was on top, so it came in.
Well, I stood it on my desk and took a series of close pictures at about every 45°. Those and the post cleaning set are available at:
https://www.dropbox.com/sh/u2hcicqd71xvoqf/AACCzf2z9lCqNF1WDxhe0H-Ya?dl=0
It is pretty obvious that the post clean start at 225.
They are not in the GMC photo archive because I am not sure it is worth burning storage for this - yet - and then maybe then not the whole set.
The picture group 217~219 makes it look very much as though the there was some damage to the threaded area that may have release the bearing from its setting. I will go into this more down the page.
If one has done much failure analysis, then one knows that nothing gets cleaned until it absolutely has to be as there may be evidence that can be cleaned away. That was a case here. But, I had to do a "blow it off with brake cleaner" to get it clean enough to carry on board.
I studied my only part for some time and then took it out the the microscope in my shop. It was then painfully obvious that I could not identify anything of interest through the remaining grease. So, it got a brass wire brush job in the parts washer and then another brake cleaner pass.
With 10X magnification, it was clear that the threaded area had been damaged fast and hard as some of the major diameter was scuffed off, the minor diameter was untouched and there was very little upset into the thread. Scratch one thought.
There was a concern that the tabbed locking washer might have rotated. This is right hand side. If it did rotate, it cause the bearing clearance to be tight enough to instigate such a failure. So, I also looked long and hard for evidence of that mode. This would have to leave witness marks in the threads and none was found.
After looking and passing off all the expected failures, I began again to look at those same picture you can see (until about the end of the month). That is when I noticed a feature that is clearest in images 220 and 227. Those gray bands are an artifact of Molybdenum Disulfide being loaded and smeared in the metal surface. For it to exist as it does after cleaning means that severe heat and load existed at some point. They were not there lat time it was open. This is what happens when MoS2 is preventing a metal to metal seizure. This would not happen under normal loads. There is/was no evidence of distress to the inner bearing area.
Ego, I am willing to conclude that the failure instigated entirely with the outer bearing, and it then damaged the stationary washer, retainer and nut enough to release the entire assembly. But, unless the "Lost" note on the area Craig's list pays off, I will never have any better evidence.
We were traveling on rough road in Arkansas or I might have recognized a change in sound (yeah -right) and ride in advance.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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