2001 36' U295. I've heard that there are two sources for vibrations in the driveline, the first being a failed harmonic balancer and the second a bearing failure in the tail shaft of the transmission. How do I discern which is causing my problem? I have checked the u-joints and they are good.
See if these links are any help:
Allison MD3060R P3 Carrier Bearing Fix (https://www.foreforums.com/index.php?topic=46305.msg470692#msg470692)
Rear Vibration Problem (https://www.foreforums.com/index.php?topic=34336.msg315610#msg315610)
You can take a flat pry bar or large screwdriver, pry up on the harmonic balancer and see if there's any play in it. Anything significant and a P3 fix is called for. Coach needs to be at running height to do this so best to drive rear wheels up on blocks. Raising and blocking will put the driveshaft in enough of a bind that you won't be able to move balancer, at least on my rig.