Vibration in 2004 F150 XL

My tires were just starting to scallop at around 12thousand and caused the same problem.

I have a 04 F150 XLT and I don't have your problem but there are many many people who do...

yep the o3/04 built trucks have some issues,, the tire wear is another issue. new specs,, replace parts if u have hancock tires,,

It could be your center support bearing.. what holds the two arms of the driveshaft together. Also, a U-joint could have slipped at this position or right where the driveshaft meets the engineblock... Any sort of friction in these areas can produce violent shaking. My guess is that you may have bottomed-out somewhere... meaning that the driveshaft slammed into the ground. The only other thing that occurs to me is if your left front tire might be unbalanced...

Sounds like the rear tires. Take them to the shop and get them balanced, and rotated. IT has to be done every 6,000mi anyway, so if you havent done it yet, then its probably too late anyway. The reason rear tires do this is because of the no-load situation on the rear of the truck. Its extremely light, so the rear tires are more apt to leave the road than the front when you hit a nice sized bump. This causes uneven wear and tires to go out of balance. Also check on the things that were already mentioned about the Hankook tires and the change in specs. Pk