i had a long talk with my mechanic about the cause. he said that since it was so far from the oil, it just doesnt get as my lubrication as the others. In my case, i had sucked up a little water through my diff breather, so the wear and tear was accelerated compared to yours. but short answer to your question, YES IT WAS THE FRONT PINION BEARING that was WORN/DAMAGED/PITTED. i have 190k on that rear diff and its components. So i guess it could have been time for new bearings anyways. Also, he said had I waited longer, it would have eventually done some pretty serious damage (had a bearing completely failed throwing metal ˟˟˟˟˟ everywhere inside the diff)---so just keep that in mind. preventative maintenance is ALMOST always better.

 

You're right about the PM. Hopefully I can do an inspection and diagnosis before I go and buy parts or labor this time. That sounds like one nasty inspection. Maybe the stethoscope can find it without cracking any diff seals and making a mess? Thanks

 

Hmm. Finally it's spring in Milwaukee. Pulled the truck in, dropped the drive shaft, and cruised around a while in 4-Hi. NOT ONE vibration! Too much excitement for me. I've suspected my center bearing because it has plenty of play, but I thought it must be normal, since it turns smooth. A tech owes me one so I'll have him replace the center/carrier bearing for me. Maybe I'll have him do the U joints as well just for the heck of it.

Thanks for the suggesty on driving without the shaft.

 

Well, with my new carrier bearing and new rear U-joint I have no vibration. I'm pretty sure the U-joint was not the problem though. Another factor was all the built-up gunk and grease covering parts of the drive shaft. I wire-brushed away as much as I could thinking maybe the buildup had left the shaft unbalanced.

Anyway after my test drive now I notice a really faint screech in the shaft. The NAPA carrier bearing wasn't nearly as loose as my original and had a fair amount of resistance to turning. My theory is the inner bearing race spins a little on the shaft at higher speeds. That could explain other sites claiming that the NAPA replacement doesn't last - the rubber appears to fail - maybe through melting as the bearing becomes hot? We'll see.