Help me find this #%*+ vibration

The culprit: 1999 F-250 diesel. 450k miles (not a misprint)

The basics: violent shaking over 65 mph.

The history: it's been doing this for over 150k miles. Never could find it- usually drive slow and avoid it.

Feels like: a badly out if balance tire or tread separating, however:

The monkey wrenches: it's been through 3 sets of tires, multiple rotations and balancing, new shocks, brakes, and thorough suspension checks. No change. AND:

It's inconsistent. It shows up when the drivetrain is not under strain (like cresting a hill). I can make it go away by feathering the gas, giving it some brake, or turning hard ( I think...a little hard to proof at 70 mph). It will go away by itself in 10 or 15 seconds (but then return). And it's not really a vibration, it's more like a lurching- violent forward and back movement that is not felt in the steering wheel.

No visible wear or damage in any suspension or drivetrain component.

It's got me stumped. Never before have I been able to describe a problem in such detail without diagnosing it.

Thoughts?

Throttle position sensor? Bad injector?

I dunno, I think Curtis is the man you need to talk to.

Yeah. I'm hoping he'll check in

Carrier bearing or a U joint is my guess.

Does sound driveline related, does "drivetrain compent" include u joints and drive shaft stuff?

Have the wheels been changed? Lug nuts could be the improper type for the wheels, allowing a little bit of slop at higher speeds.

I had a buddy who's Jeep would shake up a storm, but ran good, idled fine, and no drive-line slop. Turned out to be the lugs.

Brokeback wrote: Does sound driveline related, does "drivetrain compent" include u joints and drive shaft stuff?

Yes

Is this similar to the "death wobble" on jeeps? Maybe a bad steering Damper?

Look for a missing balancing weight on the driveshaft. Usually, they paint the shaft after tacking on the weight so if it came off, you'll see a square of bare metal.

Death wobble. Common 4x4 problem with lifts. Caster gets out of whack, causing scalloping of tires. Even without a lift it can happen. When is the last time it has been aligned? Make sure if it has a panhard bar setup that those bushings are in good shape, as that can allow the whole axle to vibrate.

And semi related to pheller's post I had a buddy who had a factory steel wheel that wasn't cut properly, making it off center. Haunted him forever.

In the absence of an easy solution, borrow a go-pro and mount it under the truck to see if you can see the vibration.

The thing i would do in your position is have someone drive next to you and tell you if any of the tires start visibly shaking when it's happening.

Check the pinion angle.

I dont know if this could be the problem, but I thought I mention.

I used to feel the same symptoms on an automatic car. It vibrated at light throttle, usually higher speeds and no load. The problem went away after I completely changed the fluid. I emptied/refilled the transmission 3 times with a quick drive in between to let the transmission shift through the gears. I think it was the torque converter that wouldnt lock up properly all the time.

PHeller wrote: Have the wheels been changed? Lug nuts could be the improper type for the wheels, allowing a little bit of slop at higher speeds. I had a buddy who's Jeep would shake up a storm, but ran good, idled fine, and no drive-line slop. Turned out to be the lugs.

+1, a buddy of mine had this happen once.

It sounds like a driveline shudder since you mention the steering wheel does not shake when this happens, the first place I'd look is a bad transmission mount. While you are at it, check the engine mounts carefully too. If any of them are oil soaked or 'soggy' (soft with a lot of cracks) replace them.

Its just a cracked front cross member. I think Ford has a TSB on it. No big deal if your not driving it. It may have a safety recall on it. If so Ford may do it at no charge.

Have the trans checked for clutch lockup pulsing.

I know you said driveline was good, does that include driveshaft splines and/or tail shaft slip yoke? And bushing?

If also take a look at the harmonic balancer and a accessories. 450k is a lot of use for the rubber in te damper. Vibrations can travel through the driveline making diagnosis tough.