A swap question:
I bought a 1985 F250 4x4 with a T-19 4spd. It originally had a 6.9l diesel engine in it and a former owner swapped a 1979 7.5 460 (externally ballanced) engine in place of the 6.9l diesel engine.
It vibrates harshly above 55 mph.
My question is there a way to tell without discounting the exhaust etc and physically pulling the transmission & transfer case?
Is the a way to tell if I have the right flywheel by pulling the access plate on the bottom of the bellhousing? If so what am I looking for.

 

Does it vibrate when you rev it in neutral?

The wrong flywheel will vibrate all the time, under load or no load, in gear or out.

If you only vibrate at 55mph+, look for bent drive shaft, bent wheel, tire coming apart, alignment issue, other bent, broken or out of kilter stuff that turns, twists, or otherwise moves when the truck is going 55+.

 

Hi 85e150six4mtod,
I tried it in neutral it didn't vibrate too bad. I can't get it past 55 mph under power.

 

Pretty sure if it was the flywheel, it would vibrate just a bad or worse in neutral. You say not "...too bad...". Are we talking buzz or paint shaker?

Another possibility is a fubar'd driveline angle. The crank and pinion need to be parallel.

Drive Shaft Harmonics

 

I checked the angles from the transfer case out put housing was at 2 degrees the drive shaft was another 2 degrees.
So I did so investigating which took all day, but it turned out being a lose dizzy cap. So I put rtv sealant on the top of the dizzy and both top and bottom of the adapter no more vibrations.
Thanks for your time and effort 85e150six4mtod.