I have a 1990 Ford F-350 4dr p/u with a 7.3 and a international 5spd manual tranny. I hear a knocking noise from the flywheel region, when going down the road the noise comes and goes. When the noise is present @ idle, when revved the noise gains speed as well. I have good oil pressure (about 40) what could this be?

 

when was the last time you replaced your clutch?
is your pedal hard to push ?
a lot of the flywheels on these desils dont have a solid flywheel and it maybe it getting ready to come out

 

Could be a throw out bearing getting ready to puke. Does it change if you have your foot on the clutch pedal and depress it slightly?

 

We know its not the thow-out bearing and there is no difficulty in depressing the clutch....I'm stumped.

 

Time for a new flywheel.

 

Springs in the flywheel are probably worn out. Nothing to worry about though, I drove mine for another 90,000 miles after mine started. When my clutch went out I replaced the original flywheel to a solid flywheel & problem was solved. By the time I finally changed it out the vibration sounded pretty bad & caused the whole truck to vibrate, got some strange looks from people that rode with me for the first time.