Follow up to posting last week. "VIBRATION IN 02 S/D"
I did the following....tell me if you think it is indeed the tires.....

1) Let the truck coast down, in gear, engine running. Vibration was predictable. It showed up at around 42-45 mph.

2) Let the truck coast down, in neutral, engine running. Vibration was predictable. It showed up at around 42-45 mph.

3) Let the truck coast down, in neutral, engine off. Vibration was predictable. It showed up at around 42-45 mph.

4) Jacked up truck, ran up to speed. let coast down, no vibration. Held at steady and variable rpm's, and the only vibration was normal resonance associated with the PSD and other moving parts...no problem


Am I correct??????? I have the Firestone A/T's.... Please let me knoe what you think. I am not confident in my local FORD dealer and don't want my flawless PSD to be their chopping block.....:

 

Makes sense to me. Mine has the same problem as per the mph that the vibration starts. I have the 265 Steeltex's. I can hear them on the road, sounds like a minor version of a mud only off road tire.(slightly out of round) Plus you can see the thread joints in the sidewall running from the rim to the thread. Not a lot of confidence in these tires.

 

Oh... That vibration... yep mine does it too, almost exactly as you describe. I had a local truck shop balance and align the front end for me. He looked at the tire wear pattern and corrected for it. The truck still has some of the same drone-drone-drone sound at 50MPH, but the vibration part is pretty much gone.

I toyed with the idea of rotating front to back criss-cross to get new tires on the front... but it's hot outside.

I believe the tires are just cheap, General Grabber AW's.

My theory is...
The alignment has some aggressive settings to improve/diminish some of the characteristic handling feeling of a solid front axle.

The tires are cupping due to this.

When you get the tires around a certain speed, the frequency of the ground strike is syncing with the spacing creating a harmonic.

Any additional vibration is amplified, such as the tire out of balance.

I had the truck aligned with a little less tow-in and made sure the tires were very balanced. The sound and vibration has much improved, but I do have to admit I've gained a little more bump steer... though not much.

Robert

 

Good test! That pins it down to the front end probably front tires. The most likely source force to excite your "resonance" is simple single plane imbalance, next couple (multi plane) imbalance or out of round tire. A tire out of round can be mass balanced but produce a mechanical reaction force from rolling road contact. I remember that you wrote earlier that you had your tires balanced at <= 1000 miles. Could be that they did not balance them very well in the couple plane? Tire balancers these days are very accurate, the operator need know very little about the principals involved. Normally I would advise to rebalance the tires. But the would cost you again. How about changing the rear tires to the front, one side at a time with a retest in between. It is unlikely that all the tires are unbalanced or out of round. You might be able to identify the bad one that way. Let us know how it goes. My F250 CC PSD had a little of the same thing at 65 MPH it went away at 6,000 miles.

 

I had Steeltex R4S's for a week & noticed the truck was quieter & handled better after I switched to BFG AT KO's.

 

The tires were balanced by the same shop that does our Over The Road trucks. No charge!!!! I actually stand there and watch, or even do it myself....they hate it when I come in, so they usually just let me do it myself...These things are positively zero'd out on the balancer. I even calibrate it just before I use it just to make sure.
I am glad that I am hearing about the same problem with others. I will rack up a few more miles and see how the tires wear. I will probably run them for a while and see how things work out.

Thanks for all the helpful responses.....

CEEJAY

 

If you have factory steel wheels give them a look over for runout.At least two of mine were garbage.I replaced them with Forged wheels and new tires and it took much less weight to balance the tire and wheel assy.