I have a '02 Explorer XLT 4X4 w/ the 4.0L 6 cyl, and have recently had the vibration problem arise. I can feel this low rumbling start at 30 MPH or so, and continues to the really noticable 60-70 range. My vibrations seem to be more severe on acceleration, and subside a bit on deceleration (off the gas). My truck spent 3 days at the dealer this week, and no luck. They did tell me that they checked the driveline for runout and rear diff and all is normal. I wondered if it may be torque convertor related, they said they checked it too and it is ok. They went through some other troubleshooting that lead nowhere. I guess that they checked the tires, and nothing there too. I have the truck back, and they are saying they are "awaiting service repair information", evidently that means info from ford engineering on what direction to go next.
Dang, and this vibration happens just 6 weeks after having a entirely new rear differential put in. That service took 3 weeks due to lack of available parts. I took it in then because I noticed a bearing droning sound in the rear. Evidently the rearend was eating itself up. I have heard that the aluminum diffs of the IRS have been problematic (??), which is a shame... I really love the way this truck drives.
While it was in for the rearend repair, I had them rotate and balance the tires, I can only wonder if that may have anything to do with my problems now. I read references on rotating that said to "cross rotate" tires??? I thought these days you were only suppose to rotate front to rear, because crossing makes the tires roll in reverse and can lead to tire problems like belt seperation. I am going to ask them what method they used.
If anyone has any insite, comments, or suggestions, I am open to all. Thank you, Roc

 

Did they bother checking out the rubber mounts and mounting bolts ie; tranny mount, rear differential mounts etc. I had a similar problem with my 81 Datsun 4X4 when I swapped out my final gear ration in the differential and put in a new clutch. After driving it down the street I had the same symptons. It ended being that I had the tranny mount bolts were not torqued down. Hopefully it's something simple as that. Good luck