I have a 2005 F 150, 2 wd, 5.4 L, 108,000. In the last few months I have noticed an odd low frequency vibration that occurs between 45 and 55 mph. It seems to come from the rear end as I can see the tailgate bouncing up and down in the rear view mirror. I had Big 10 tell me the factory steel rims were bent, but if that were the case it seems like the vibration would occur at all speeds, more so at higher speeds. Anybody run across something like this before? Also, at 65 mph or higher I get a higher frequency vibration through the steering wheel. Could this be wheel bearings? Any help would be appreciated. Thanks.
A vibration that is speed sensitive helps diagnosis the problem. In this case the vibration is between 45 and 55 MPH. This sends me right to the drive shaft. It could be a bad center bearing, worn universal joint and even the drive line angle could be responsible to the problem.
Remove the drive shafts and check the movement of the joint in the shaft. It may be fee moving in one direction one way and be stiff in the other.
Other problems can cause the problem like the rims as you mentioned, a tire tread or belt in the tire could of separated, out of balanced tire, the list goes on.
Check this suggestion out and let us know how you make out.