StorminMatt

I have to admit that I have NEVER worked on an F150 before. But a friend of mine is experiencing vibration while driving the truck, ESPECIALLY during acceleration. My first instinct was that one (or more) of the u-joints is probably bad. But after getting under there, none of the u-joints seems to be worn or 'sloppy' - they are all tight. On the other hand, it seems like there is LOTS of movement in the driveshaft. The center bearing moves a pretty good deal inside the rubber that supports it - DEFINITELY enough that it is quite visible to the naked eye. Also, there is LOTS of movement in the slip yoke - it makes a DEFINITE 'clunk-clunk' sound as you try to move the driveshaft back and forth. I don't have a known-good F150 to compare it to. But I compared it to a Toyota Tundra (which also has a two piece shaft). And there is VERY LITTLE movement in the Toyota, and no clunking. Can I assume that this movement is excessive? Also, if there is excessive clearance with the slip yoke, I'm assuming that transmission output spline might be excessively worn?

Moose_God

I'd replace the center bearing then....sounds like your culprit.