I remember reading about some F250s having a vibration caused by a chassis harmonic? Can't find anything about it. Anyway, here's where I am...
2015 F250 supercab 4x4 8' bed 6.2L gas.

Intermittent vibration between 60 and 75 mph. The vibration feels about 5-10 hz. Lasts about 5 seconds, then stops about 5 seconds, then happens again. But sometimes, won't happen for a few miles. And on very smooth roads, doesn't occur or is VERY VERY faint. At the other other extreme, it's very annoying.

Rims (without tires) have been measured for balance and run-out, and are within spec. 2 sets of tires, both having been road-force balanced, and little or no change. Tire pressure doesn't seem to change it, and changing damping in the adjustable shocks doesn't seem to change it.
Pulling a trailer seems to change it, a little.

I'm considering getting some sulastic shackles to see if that dampens the vibrations and/or changes the harmonics. But...that's a $400 guess.

Anyone heard of this or had this same/similar problem?

 

This may or may not help you, and I know it’s a different animal, but here goes. I noticed a very similar vibration after I lifted my truck, I used tapered blocks and should have used flat blocks. This was enough to change my driveline angle and cause the vibration. I’ve also had u-joints cause a vibration like the one you have.

You out put a trailer on and it loads the rear of the truck, that changes driveline angle. I’m wondering if this could be your problem.

 

That's a great observation! I have 2" lift blocks in the rear.
Pulling those rear lift blocks isn't that difficult.

THANKS!! Food for thought for sure.

Also, I've checked the u-joints several times. They seem ok.

 

I sure do hope it’s that easy for you, I know how crazy a vibration will drive me. I’m imagining that you might be the same. Also, does your pinion flange have multiple bolt locations? One thing I tell my mustang buddies is to mark the driveshaft/pinion flange location, then unbolt and turn it to the next hole. That change the driveshaft to pinion gear indexing and sometimes that fixes vibrations too.

 

I hope so too! I'll send beer if it works out.
I'll check the driveshaft flange.

 

If you don't want to read all of this I don't blame you.
I think the root cause of the chassis resonance at 70-80mph was the frozen front driver's side lower caliper slider pin...this a known trouble spot with these trucks. It was keeping just enough pressure on the pads to drag on the rotor and it showed up at 75mph.

Your on your own from here I didn't proofread this,
Please join me on my journey from hell last July:
This is my diary written last year of the BS.
Truck was very close to being pushed off a cliff with a rag hanging from the gas tank, still could happen.
It's still not 100% as I think its pinion bearing time thanks to the incompetent stealership tech. The truck currently has 85K miles on the clock. 2011, 6.2.

Here we go....start reading this from the bottom up..see red font below.

-Sept 15th, More time on my back. Pinion flange has up/downplay! Are you kidding me! About .010-.015” Had to Discon the driveshaft to feel it. (again!) Didn’t have a large enough socket for the pinion nut. Had to go to Sears and purchase a new ¾” drive socket set 2 additional sockets and one additional short extension. $240. Tightened pinion nut approximately 70* so almost ¼ turn to get rid of all the run-out. Dropped the diff fluid. It looked like butterscotch. Not burnt more like water contam. The cover looked like it might have had a small leak at the top from the factory. 3 pints of 75-140 Valvoline. Road test was encouraging. Took it to/from work 120 miles. Much better but I still hear a warble resonance that has a sinusoidal sound at 75-80mph. I think the pinion bearings are damaged and will eventually need replacement. Or the driveshaft needs to be rebalanced or there’s another bearing going somewhere. I’m gonna drive it for now. $240 socket set +70 dif fluid= $310 plus 4 hours my time not including the run to sears. Stealership replaced the pinion seal at 38K and the GD useless tech didnt set the pinion up correctly. Again another job I farmed out and have to go back and fix correctly MY SELF! Disconnected the rear drive shaft AGAIN and road tested with just the front shaft. Noise gone. Looks like Ill be gutting the rear axle. Might as well replace the rotted brake plates...or just push it off that cliff.

-Sept 1st, Problem still not solved. Thinking maybe brake rotors are rotted and unbalanced. 4 new rotors 2 sets of pads. $360, 6 hrs.
While installing brakes (last wheel of course) I found a bad slider pin on the bottom side!!! F-ing $14 pin was likely the root cause of all of this! Of course, its Saturday and nobody open sells just the pin and boot, must buy the whole caliper and bracket! Enough money dumped into this POS! So I heated the pin and managed to get it out. It was stuck. Cleaned it up, salved it up with copper anti-seize and RTV’ed the torn boot and noticed a pinched caliper piston boot. RTV’ed it too. Dam truck! Rides much better now. But still some resonance at 70-80mph.

-Sept 1st. Took shaft out again. Inspected joints. All ok. Centered them better, pushed caps together to make sure there was zero movement/play another 4 hrs.

- August 29, 4pm to 7pm. Dunn tire another spin balance! Free of charge. The road force didn’t catch all of it one tire was 3 oz off. 3hrs. Road test, still not right.

- August 28, 3pm to 7pm. Dunn tire, $90 road force, worse than the initial spin balance! 4hrs.

-August 22, 8am until 4pm, Dunn tire, $540 for 4 new tires plus $60 for other crap, road hazard, and alignment. 8hrs. Michelin warrantied all 4 tires...Prorated this is what it cost. New rubber vib still there.

-Aug 21st Took shaft out again as I noticed the caps on the trans side were not seated well. Ujoint had play! They were pushed too far towards the clips causing joint play. Took back to Fleet pride they simply knocked it with a hammer to tighten up joints and handed it back to me, gah! Vibration still there.

-August 20, My time and gas to R&R the driveshaft and deliver to a shaft shop, $125, Spun balanced the rear driveshaft installed 2 new U joints. No change in vibration. OEM Ujoints were fine, but they have to be removed to balance the dam shaft.

-August 3, 4 new Rancho 9000 series shocks $400. 2 hrs. Better. A vast improvement over Ford shocks. Vibe still there.

-Starting around mid-July had four different shops spin balance the newer Michelins with zero luck. You could see 2 of the tires hop. That's 4 x 60 dollars so $240 in wasted time and money. 6 hrs



37+ hours of MY time wasted for a 14 dollar slider pin!

Rear Shaft in and out 10X!

$2,125 in parts.

Another $160 for new battery cuz it couldn't wait to shizt the bed

$2,185 total in a month and a half to fix this...lovely truck. This is mostly my labor so double that $4300 at a shop or stealership.
Im buying a Yota!

 

I had my own experience with this when i replaced my OEM Michelins with a cheap set of Nankangs Conquerers ATs. Obviously Chicom tires. The tread was great and worked well in the snow as they were severe weather rated. My vibration started at about 45 mph and stopped at just over 50 mph. Then I had a slight one at about 70 mph. I had the rear two replaced as that's where the vibration came from. Same thing again. I ended up buying a set Of Michelin Defender LTX M&Ss and it went back to the smooth OEM ride. My conclusion is that cheap tires from China do not help these trucks and probably exacerbated the problem that can happen with longer Ford trucks. These trucks from different years, esp with the longer wheel bases, have the potential to do this. There's all kinds of causes as well. Here's some old threads for you to read through:

https://www.ford-trucks.com/forums/1...40-45-mph.html


https://www.ford-trucks.com/forums/1...pping-tsb.html


Here's the seaarch i did:


https://www.ford-trucks.com/forums/s...rchid=29071767