Ford F150 2002 4.6 liter xl crew cab full bed,95000 miles. I have a bad vibration starting at about 30 mph, really shaking good at 45 mph and persists at higher speeds. MY first thoughts was i lost a wheel weight . Took it to Costco and got tires rotated and balanced. No change in the vibration. Next thought it must be a Ujoint. this truck has 2 rear driveshafts and a center bearing replaced 3 u joints and the center bearing. No change in the vibration. You feel the vibration In the seat first . Tires are bridgestone P235 70 r16 about 25000 miles and look new. Out of ideas!

 

Has the rear end been under water in the past? If it's a LS and if the fluid has broken down or been contaminated......

 

No dont think it could have been that I have changed the fluid twice, Once when i first got the truck (21,000 miles) and again about 50k miles after an axle and bearing rear bearing replacement.

 

Yeah I doubt it then...

You can inspect the driveshaft for a missing weight (s) front and back. All I can think of at the moment. Look for like a round or oval clean spot on the shafts themselves.

 

Could be an issue with the transmission. If you have exhausted all easier issues might want to consider a transmission fluid flush.

 

Road tested the truck got it up to 45 Put it in neutral foot off the gass no change in vibration.

 

Have you checked your wheel bearings?

 

That is tomorrows project.

 

When checking the wheel bearings check the e-brake might still be slightly engaged as well. Long shot but worth checking since you’ll have the wheels off the ground.

 

Sure sounds like an out of round tire to me (slipped belt, football sized lump)
Especially if you feel the vibration at 35 miles per hour, in the seat of your pants
Look for a football sixed lump on one of the tires, as you rotate the wheels around on a jackstand
Pretty damn common to see a slipped belt on a radial tire these days
U joints and driveline woes generally won't show up until speeds of 50 and above, then get progressively worse as speed increases
Same with tire balance, speeds of 60 and above is where wheel weights come into play