97 PSD, 4x4, F350, 4D, 5spd std.

While accelerating a vibration can be heard and felt through the floor. It goes away when I let off or get to cruising speed.

I havent had a chance to crawl underneath (its raining).

I think it maybe the carrier bearing.

 

sounds like a carrier bearing or u-joint

 

Yep - my first thought is carrier bearing - then check your u-joints. Also - while you're under there - check the transmission mount - I had one of those go on my old truck, and it actually took out both my front and rear driveshaft u-joints 'till I figured out what the problem really was!

 

Well......we think it is the flywheel. I aint happy. Dont they cost like $1200?

 

If it's the flywheel than the vibration will be ENGINE RPM RELATED. Never from vehicle speed. You would be able to duplicate the vibration just revving the engine in neutral. Driveline vibration is always vehicle speed related, and in most cases, you can put it in neutral, coast, and still feel the vibration. I have to go with all the other posts here, you have a bad U-joint or something that is getting skewed under load and creating the vibration.