I have a 1998 F150 2x4 4.6 auto S/C long box with 258000km
Friday morning after a long drive the day before the It just started shaking with bad vibrations from the seat up through the steering wheel and dash. The truck seams to not to have any power but it also shifts fine.
This happens when getting up to speed and staying there. When you get off the gas the vibrations stop, if you shift into N every thing is fine. If I drive with the overdrive off it doesn't seem as bad. When you step back on the gas the shaking starts.

It was wet Friday morning and my 1st thought was the wires were wet and there was a bit of misfiring. But after shaking for 15km it was just as bad.

Any help would be appreciated

 

Hi and welcome to the site!

I would start with the U-joints on the drive shaft. Inspect them for wear. Next I would look for loose motor mounts and tranny mounts.

Good luck,
Lee

 

i recently had the same problem. During acceleration no vibration but at constant speeds it had bad vibrations. Torque converter was the problem.

 

I have one universal loose on the front,there are 3 total. My mech. said the plugs might be the problem. I'm due for a tran. oil change any way so it's going to a tanny shop in the morning. I've got fingers and toes crossed that it is only electronic or the plugs.

 

It wasn't the tranny. I changed the plugs and the vibrations have stopped.