Intermittent vibration at 70-75 MPH? - SOLVED!

[kep5niner]

I’ve been chasing a vibration that has developed in the past month, at speeds of 70-75 MPH. I briefly mentioned it in @whtbronco thread, but didn’t want to derail his quest. I first suspected drivetrain, as it seemed centrally located in the vehicle, not one of the corners. The tires are new, and were smooth as silk after installation about 6k miles ago. I had them balanced and rotated as a matter of typical maintenance, and initial troubleshooting. It did not solve the vibration.

The vibration was higher frequency, almost to the point that the image in my rear-view mirror was blurry / unusable. Not in the steering wheel, but slightly in the pedals. U-joints checked and found OK. Trans, front end, rear end and transfer case all recently serviced and fluid levels correct. New bearings on all four corners. All ball joints, shocks, and tie-rod ends are good to go. Breaks are all new Motorcraft.

But on my latest 60 mile commute to the airport (all highway), the vibration inexplicably disappeared. Do I have a self-healing Expedition? Back to reality, what other ideas might it be?

 

[whtbronco]

So my vibration was inconsistent. It was always present the last few months, but sometimes kind of minor and sometimes pretty severe from my perspective. As you may have noticed I have found several contributing factors. Rear driveshaft had a very minor curve in it, the slip toke had play, the front u-joint had a tiny bit of play. I got news tires and they were balanced properly. Then I had to recheck things I already checked or replaced. It was on the 3rd of 4th check of the front driveshaft I found a failed u-joint. I saw a tiny line of clean silver metal about 1/8" from the cup on the trunnion. That u-joint had no rotational play still, but I could move the trunnion left-right(into and out of the cup). That was the source of the inconsistent vibration and it took multiple times for me to find that, just happened to be to the right place in the rotation and I saw it. Course now I think I am on the last bit of vibration with the transfer case, we'll see.

All I am saying really is make sure you check very carefully when checking, I was too quick I suppose and missed things the first time, second, third. Now having been a heli mech I suspect you are more inclined to notice the little things that some of us would miss at first.

Since you think it's a high frequency I would look at the driveshafts inward towards the transmission, maybe including pinions. The differential, axles, wheel bearings and tires should be a slower vibration since they turn 3-4 times slower than the driveshafts and such.

 

[kep5niner]

Great tip and great feedback! I have new Motorcraft u-joints on hand, so I’ll just swap those out. And appreciate the shout out, working on helicopters for 8 years definitely gets you in-tune to all things spinning / rotating. Flying them for 18 more years even more so!

 

[kep5niner]

I swapped out the main drive shaft u-joints, and took it for a test drive. No change to the vibration above 70 MPH. I still have new u-joints for the front drive shaft, but was troubleshooting to see if the main drive shaft u-joints did the trick. Nope.

Question: does the front drive shaft spin when only 4x2 is selected? I would think no - and if it doesn’t, then that can help me eliminate the front drive shaft u-joints as a possible source of vibration. Thanks fellas.

 

[whtbronco]

The front driveshaft is not supposed to turn in 2wd, but as several of us have noticed lately they do sometimes. My transfer case was not releasing properly or IWE's are faulty.

 

[whtbronco]

I just had my wife do was drive the truck about 1' back and forth while I watched underneath. The front shaft was moving right along with the rear. I then verified the IWE's were working and started testing the transfer case and found that there was no setting where the front driveshaft could be turned independently from the rear.

 

[SafariGoneWrong]

I attached a page from the 06 Ford service manual that’s the closest to what’s being discussed, I think. I’m learning a lot from the transfer case discussions.

 

[kep5niner]

Great feedback men. Looks like swapping out the front driveshaft u-joints is the plan. I may be able to get to it tomorrow afternoon. If so I’ll report back.

 

[whtbronco]

I suggest taking it for a ride with the front driveshaft removed as well. Assuming the IWE's are working correctly the front axles and diff would not rotate so those would be eliminated as well. The good news is we can drive without the front driveshaft.

If the rear driveshaft was the same design we could also pull the rear driveshaft and then 4Hi would give us front wheel drive. I used that for isolating things many times in my older trucks. I also used front wheel drive when I sheered the rear pinion shaft or the rear driveshaft twisted and broke apart from doing wheelies in my 79 Bronco, LOL. I was 16 and I had a truck that did wheelies, what can I say.

 

[kep5niner]

That’s a great idea, and could help troubleshoot the other components as well. Wheelies in a Bronco? Well done! Thank God none of this internet stuff was around back then, or I may have had quite the different trajectory than now