My 2008 f150 scab 5.4 3.73, has had a vibration since new. You can feel it in the wheel and floor, it shows up between 70-85km.At 78kmph with the ford tech meter there is a vibration at 1440rpm and 880rpm, the 1440rpm will go away once you leave the 70-85km range.

Things we have tried....

changed wheels with another new f150
switched drive shaft with another new f150
checked rear end backlash


any ideas.....Thanks...

 

I am under the impression from your post that checking for vibrations has been done while on a lift?

How about removing the driveshaft - leaving the rear powertrain isolated - to see if the vibration is motor/transmisson related? I would think that might help isolate the problem. If the problem does not present itself at that point I would think you would be looking at the rearend, or hubs more closely.

Just my 2cents - sorry to hear of your problem and good luck!