Another headscratcher for you guys.

My '83 F250 has suddenly started having a very low drone/vibration while driving around; u joints and driveshafts seem solid, exhaust hangers are good.

Seems to be worse with higher speeds, but I can't quite place my finger on any specific area of the truck that vibrates more than any other.

While driving downhill on my way home today, I put it in neutral at about 60ish mph, vibration continued. Got home, parked, and held it around 2k, maybe 2500 rpm, vibration was there, or at least a very similar vibration.

Took a look at the motor mounts as best I could, but that wouldn't explain the vibration when rolling downhill in neutral, as it doesn't vibrate at idle at all.

All the suspension components are new, except for the leaf springs. Only thing I haven't replaced are the hubs/bearings, but I don't hear anything out of any of them while driving or turning.

Tires are all recently rotated and balanced.

Any idea what else might be the cause?

 

If you are sitting still in the driveway and have the vibration when revving the engine, it's not going to be suspension, tires, driveshaft, any of that stuff. Only the flywheel, engine, engine accessories, engine fan, etc. That is the only things that are moving.

P.S. If you didn't have the clutch pushed in, then some of the guts of the transmission would be turning also.

 

Right, which is why I am posting this question; my guess up to today had been suspension. I am aware of the fact that something else is vibrating after the downhill test.

And to the second point, yes I had the clutch pushed to the floor while coasting, vibration did not change with clutch in or out, in gear or in neutral, I tried each combination, I have a long downhill stretch where I do these tests.

 

yup thats a head scratcher

 

Sounds like a pressure plate issue. Not common but it does happen a spring in the plate may have broke and dislodged throwing the pressure plate out of balance.

 

How about the belt-driven accessories, or the belts themselves?

Since you can duplicate the problem while parked, have a helper hold the throttle while you watch the belts and accessories. Check the tension on all the belts. You can even remove the belts and see if there is any change. Just be careful as you can only run briefly with the water pump not turning.

 

[QUOTE=kr98664;17535202]How about the belt-driven accessories, or the belts themselves?

Since you can duplicate the problem while parked, have a helper hold the throttle while you watch the belts and accessories. Check the tension on all the belts. You can even remove the belts and see if there is any change. Just be careful as you can only run briefly with the water pump not turning.[/QUOTE]

X2 what kr98664 said.

 

Alright, a quick update:

I have confirmed the vibration is not coming from the engine; I did some testing yesterday and this morning.

What I am now fairly certain of: One of my u bolts on the front passenger spring lost a nut, so my right side is only held on by a single u bolt that is actually doing anything. So, if I'm no fool, I'd imagine that's what it is.