Our F150 will suddenly start shaking. Usually happens at around 45 mph. Sometimes it is so bad that you have to pull over. It doesn't happen all the time but enough that you can't drive it on major roads for fear of it happening. We have had it to the dealer 4 times and they have realigned it but can't find anything wrong. It took 3 visits until they actually were in it when it happened. It has less than 6000 miles on it. Has anyone else ran into a problem like this?

I've never heard of this happening. I would take it back to the dealer and demand something be done. (Tell them your in fear of your familys and friends lives [because i would be scared if that happened])

Thanks, that is our next step. The dealer is waiting for Ford to get back them in the next couple of days and depending on their response that is what we'll have to do. I was just checking to see if there was some type of problem out there that we weren't informed about.

It could have something to do with the wheel bearings, I'm not too sure.

Thanks, we'll check that out and let you know.

I have less than 4k on my thruck and it has done the same as yours three times. Slowing down doesn't stop the shake but if you stop it goes away. I think there is a drive train problem in the rear end. I have compared the axle freeplay in mine to three others. My trucks appears to be excessive. It is going in the shop next week.

Check tire balance also. they don't always check it with an alignment.

Okay, this is probably too late for the original poster but it may help others. I bought a 2004 F150 w/ 30K on it. Drove it for two weeks and it was fine. Then I had the following happen three times, on 3 different days. Driving along I'd all of a suddne get a violent shake in the whole vehiclethat felt like the rearend was locking up. this happened when driving at 45mph, 70mph, then 10 mph. each time the problem went away by itself. The problme was actually caused by the emergency brakes!

It seems as if the e-brake is a mini drum machined into the rear brake rotor. The e-brake cables would freeze up and the brake lock on causing the rearend to shake/hop. Still can't figure out why this would happen all of a sudden while driving but lubricating the cables, remachining the drums and replacing the e-brake shoes cured the problem.