Odd issue here, I am kinda stumped.

On the highway WITH a passenger the truck vibrates violently over 80mph, if I then let off the gas it vibrates almost worse until it slows back down to around 65mph.

With no passenger it is as smooth as silk way past 100mph.

but then again sometimes it is smooth with a passenger, and sometimes virbrate without a passenger.....so basically it is very inconsistant.....is it possible something is moving around and depending on the day will or will not cause the vibration.....

I have ruled out the wheel/tire balance, as they cannot go out of balance on tuesday and be fine on wednesday.

Driveshaft angle is a constant and does not change when cruising at 80mph.

My only guess is a u-joint or the driveshaft yokes.....

I'm stumped.

I also have a clunk when I hit the gas while coasting off throttle on the highway.

I run a Detroit truetrac if that makes any difference.

My girlfriend is usually the only passenger in my truck....LOL so I blame her

 

Pit do you feel it in the wheel or the seat??? sounds dumb but its a way of telling front or back. You may want to check your front wheel bearings, for proper pre/load and grease. Also a pinion bearing starting to go bad. just some places to start. Artie

 

I guess someone needs to ask the question. How much does she weigh?

 

I think you are on the right track with u joint
probably have one that is seized
mitch

 

Artie I feel it EVERYWHERE but not in the steering.

the GF is not that heavy....LOL

I guess it's time to drop the driveshaft and see whats up. is there a wiggle test of some sort to test the pinion bearing?

 

I had a similar issue on my F150 (Not my L). Symptoms were exactly as you described. Solution was bad needle bearings on the u-joint. Was intermittant and progressively got worse. They were so dry and stiff that i couldn't move the joint by hand after I removed the driveline.

 

Have your girl friend rotated and balanced.

 

Sounds like the U-Joint too me as well Ian.....
Lot's of Sex will help the GF lose weight thou. I prescribe both.

 

I already tried that, she got mad and said it hurt that way !

 

u-joint = cheap

driveshaft =

but other than road force testing the tires it seems to be the thing. I have to get under there and man hadle it a bit.

thanks G

 

More spiT. s0o0ory.

 

you're a nasty dirty little boy....LOL I use mobil 1