I am really stumped on this.

I have a 2006 5.4L 3v FX4. I have 4 brand new Firestone tires on the stock rims. I have recently took it in for balancing and alignment.

Here is what the problem is. When I start to get around 50mph I start to get a vibration from what seems like my engine, transmission or front end. I cannot narrow it down. It seems like the transmission is geared too low and the engine is having trouble keeping up. Something along those lines. There is no issues when I go above 60mph or below 45 mph. I am ready to pull my hair out on this.

Thoughts? Ideas? Anything ????

 

I had the same problem with my 05 FX4. I had previously had an alignment and wheel balance too. Turns out the wheels weren't properly balanced.

 

Bingo! Either that, or the tires are out of round.

 

I agree with the tire/rim senario.
Thats probably the problem.
However bent frames can deliver the same symptoms.
Any premature tire wear?

 

Rotate the front tires to the back and see if the problem moves. If so, BINGO. Take the tires back to where you bought them and have them checked out. Take the Manager for a ride.

 

I would but the dealership put on new tires so I dunno what I can do. This is a used truck.

 

You can lift the truck, and spin the wheels to check for out of roundness. Place a board about an eighth of an inch from the tread and spin it to see if they are truely round. If not you may have a bad tire OR a bent rim, it CANNOT be balanced.

 

I will check that out here on Monday. I will have to get my jack from my father-in-law. I have a feeling it is a bent rim, but why does it only do it at that range? Tires maybe cause the vibration at that frequency?

If it isn't the tires or alignment, what else could it possibly be.

 

A bent rim or an out of round tire can do weird things. I believe it is a frequency thing. Too slow, the vibration won't be noticed, obviously. Then when it reaches the correct rpm to reflect the vibration, it can then be noticed. When it goes fast enough with the weight of the vehicle, the tire can be hitting the road on the high spot and obtain a smoothing out point. All a guess but makes sense if you think about it. If you have any friends with the same vehicle wheel types, swap with them for a test run to see what happens.

Also checka nd make sure that the tire guys tightend the wheels down good. Human error can produce tremendous impacts!

You mentioned something about engine speed. Do you have a tach? what is it indicating during this vibration range? Maybe it's not the tires????? The tire swap with a friend would tell the tale.

 

i had the same vibration on my 2001 f150. i thought it was the drive line (i lowered it and didnt use the axal shims) but when i got my exoust done the vibration was fixed. so chech it. i dont know how but that might be it.

 

The tach is somwhere around 1500 when it does it. This things seems like it is floating on air as long as I am not driving around 55mph.

 

Try keeping it out of Overdrive and run the same test with the same speeds. Does it do it then at the same speed but different rpms? If so, I'd say tires, wheel or drivetrain related. If it does it at a certain rpm, then try to duplicate it in 2nd gear at the same rpms. If you get the same symptoms that are associated with rpms with different speeds, then I'd start looking at engine or transmission.

FYI.....A bent driveshaft or bad U-joints can cause bad vibrations but usually do not go away at higher speeds and have nothing to do with rpms.

 

like i said elsewhere, my horrible vibration issues were caused by out of align front end (camber was visibly off, the toe was in 1/2" and my caster didnt look bad visibly) i fixed all that, it came and went for some reason. later i rotated tires because i had cupping on the RF and felt it needed to go to the rear. while kicking my RF to get the wheel to unseat i noticed the wheel moved across the horizontal axis. my idler arm was loose.

now its barely noticeable.

 

I tried it last night coming home without Overdrive on. It did a lot better, but still a little bit noticable. I guess I am going to have to start harassing the dealer that I purchased it from since I picked up their extended drivetrain warranty in case something like this happened.

 

On a side note, it seems to only do this during acceleration or when I have the gas on. I am guessing it is tranny or engine related. I am gonna have to fight tooth and nail with the dealer on this one probably.