Please give me any suggestions as what the problem could be.

My truck is a 2005 Ford F150 XL 4.2L single cab. It all started when I replaced my tires. I have a vibration that makes my bed bounce between 50-55 mph. The vibration is felt when accelerating and slowing down at the same speed. Since then I have changed my rims, shocks, u-joints, new tires again. My transmission rebuilt but the problem was there before and after. New front and rear shocks. I recently changed lower and upper ball joints.

According to the dealership when my truck was still under warranty they replaced driveshaft and differential (I really don't think they did anything).

Could it be the driveshaft?

Thanks for any input.

 

Anyone?

 

It could be driveshaft...
Is it felt in the steering wheel?

 

No, you can feel it on the back of the truck and see the bed bouncing.

 

I have a bad hop in the rear too however it only occurs when braking. In my case I suspect brakes. If you have balanced your tires recently the only thing that comes to mind is that one of your new shocks are defective of the wrong size. If the bed is shaking so much it would have to be tire hop and if the tire is balanced And in good shape that would mean that the shock is not doing what it should be doin and the truck is bouncing on the spring

 

Mine does the bumping to when I give it gas at about 55 up

 

The problem has existed before and after new shocks. New rims and new tires so that will rule out a bent rim or bad tire.

Can a defective shock do that and just at certain speed?

 

Well it's usually around that speed that you can tell that your tires are out of balance and if your shocks are shot they won't stop the tire bounce and the hop can get pretty violent. Now if you noticed no change of any kind when you swapped shocks then perhaps it's something else. I would at least inspect shocks to make sure there are no visible oil leaks. Like I mentioned in my previous post I have an unresolved vibration in the rear but only during moderate braking. I had a prior very strange high frequency vibration at around that speed and it turned out to be tire balancing and it had only been around 5k miles since my prior balancing but I guess that was enough.

 

I have posted about this many times. No one can ever seem to find the answer to this problem. My truck has done it since the day I pulled it off the lot. With only 11 miles on it.
I had it back to the dealer many times with changed wheels, tires, rebalance of the drive shaft, etc. Always around 50 mph. Only the drivers side rear bounces.
Now I can only assume, and we all know what that means, that it has to be something that affects the balance of the tires. I say this only because if I have them balanced, it will drive smooth for about a week or two. then, back to the bounce. And that's about 1,000 miles. I drive a lot.
I usually just try to avoid that speed. If anyone ever does figure this one out, I'm sure there is money to be made. LOL

 

Same thing happens to my truck. Maybe a better shock or leaf? To make the rear suspension a little more stiff. Who knows. It is annoying that we can ride our trucks with out keeping and eye on the speed. Or what could be different in the suspension that makes our trucks behave like this. And for sure my truck didn't do it when I bought it. The only reason I don't get rid of my truck is because it's already paid!