I got an 08 FX4 with the 5.4L with 3.73 gears. Only 22000kms on it and not even a year old and I have a vibration problem. No this is not the tires problem like 50 million other people have. Here is what I've come up with. Above 120 kph when completely off the throttle I get a vibration through my seat. Similar to going over rumble strips on the side of the road. The vibration goes away as soon as you touch the throttle. Shifting it into neutral does nothing to make the vibration go away. When you lock out overdrive and have your foot off the throttle there is no vibration but when you add a small amount of throttle comes back and goes away as you add more throttle. It seems to get worse the longer you drive on the highway. In addition i get a cyclic groaning noise when you hit 4000 rpm and is goes away at 5000. This happens no matter what the speed. I don't know if its related to the driveline vibration or not.

The conclusion I've drawn so far is either a pinion angle problem or a partially seized u-joint. This is reall annoying considering I do drive a lot through the mountains and coast down a lot of hills often picking up speed.

Anyone got any thoughts or opinions. I really need help on this one cause ford seems to be useless when it comes to problem solving issues that aren't on a tsb and I haven't turned up anything similar search over the internet.

 

sounds like a bad u joint,

 

drive shaft could be out of balance
bad U-Joint
parking brake could be sticking slightly
bad differential or ring and pinion

 

Appreciate the input. The biggest problem is getting ford to do something about it. Due to the fact that it happens over the speed limit ford can't road test it and are prevented from doing warranty work on it without confirming the symptoms. I don't know if you'll be able to feel the vibration through the passenger seat or not. I do know you can here the groaning though, at least with young ears. The one mechanic denied hearing it even though I've had two of my buddies inform me of it previously.

 

yea i know what you mean, when i worked at Land Rover, we would have customers complain about vibrations at 100mph, and our insurance wouldn't cover us if we chose to drive that fast, so it went back to the customer without any repair done.

 

I know this sounds crazy but you may want to try loosening the mounting bolts for the exhaust system and then retighten them. I recall a few issues several years ago with a few F-150 and Mustangs where the exhaust systems would distort and generate a vibration. There were only a handful of these that we found. The whole exhaust system would start vibrating at certain speeds. Loosening the system would relieve the tension and it would redistibute it when it was retightened. Sounds like yours may also be heat related as it gets worse as you drive. It's a shot in the dark but it might be the problem.

 

I'll keep that in mind and tell the dealer the next time I take it in. I hate unsolved mysteries, especially ones that involve vibrations, rattles or squeaks.