Output Shaft or Bearing

[Yardsale]

'01 Job 1, 176,000 miles.



I have been trying to diagnose a vibration for over a year. This begins at 77 MPH and continues until I slow-down from fear that something will fly through the floor.



I recently re-geared the differentials, which helped localize possible sources (vibration now at lower speed, which excludes axles as a possible problem area).



I tried pulling, prodding and jiggling all the rotating drive parts, but couldn't determine the source.



I have balanced both drivelines and replaced all U- and CV-joints. Then, just for fun, I went pulling, prodding and jiggling again. Now it seems that the transmission output shaft has some play. (Sometimes, you just gotta wait for a failure to know what’s wrong.)



The shifting is a bit slow, but not terrible. Other than this, it’s fine.



I am taking it to the shop for diagnosis. Here's my question: With the amount of miles on the vehicle, if it is determined to be something output shaft-ish, might it be best to get the transmission rebuilt (with a few improvements) or let it be? I suspect that the output shaft fix would be a fairly low-cost item, so applying any labor to the rebuild would be a minimal cost reduction to doing a rebuild later.



Thoughts?

 

[Yardsale]

I took it to the shop and they checked the driveline angles. Said that the front and rear angles were farther off then they would liked. They raised the rear of the transmission a bit to correct.



Then they put the rear on stands and ran it. Three was an incredible vibration and noise. The front of the driveline could be seen moving. Replaced the U-joints. Vibration remained.



Checked the transfer case rear output shaft for play and it was suspect. Rebuilt the transfer case (new bearings, chain and seals). Found the transfer case rear output shaft bearing with more play in the case than acceptable. There is polishing in the case from the bearing moving along the output shaft. Had the rear driveline balanced to ensure acceptable balance and run out.



Drove it without the rear driveline and still felt the vibration, although it was less pronounced it was within the same speed range. I believe this eliminates any front-end parts. I think the added mass of the rear driveline accentuates the vibration that is in the transmission or transfer case.



Reinstalled the rear and removed the front driveline. Drove it and the vibration is still there at the same speed range. The vibration is a bit less, but probably due to the new transfer case output shaft bearings.



I know there is a TSB (05-20-11) on a vibration between 75 and 80 MPH. The repair is to replace a steel driveline with an aluminum driveline. I think this is a band-aid that covers-up another defect by reducing the mass of the driveline and raising the speed at which the vibration can be felt. Maybe raising the speed enough so that the governor kicks-in and the vibration is not felt, but only because the speed where it would be felt cannot be reached. This may seem a bit cloak and dagger, but who knows, it could be.



I am trying to determine what could be the culprit. Assuming that the both drivelines and the front and rear axles, and associated parts are okay, my current theory is that the problem is either the transmission output shaft, bearing or housing or the transfer case output shaft or housing.



So, what’s left? Is there maybe an inherent defect in the transfer case housing? If so, can this be repaired – are all transfer case housings defective??



Is it possible that a defective transmission output shaft, bearing or housing can affect the transfer case output shaft, bearing, or housing? It seems to me that this is probably not the case and that maybe the transfer case housing is now defective due to the beating it has been taking over the miles.



Any ideas?