81 300sd sudenly lost all trany function
 

it happened after slowing down for a turn .I accelerated and the engine and trany did not respond I then rolled to a stop and checked all positions and still no response I then checked the shift rod and the yolk and those were fine I am curious as to what internal issue could cause this symptom.any help will be greatly appreciated.

Forgive me for asking the obvious, but the fluid level is ok?

yes
 

\fluid level is ok/a little high imn wondering torque converter?

If the vehicle refused to move after coming to a stop, the problem sounds like a B-2 piston. My vehicle did the same thing - I went to accelerate out of a light, and the engine just revved and revved. With that being said, you must first check to ensure that:

1. There is enough fluid in the transmission.
2. If enough fluid - when was the last time the tranny fluid filter was changed? A severely clogged filter could restrict fluid flow sufficiently as to cause a non functioning transmission.
3. Was there any unusual vibration, noise, etc, preceding the failure?
4. Will the vehicle move in reverse? If not, the B-2 piston is not the only problem.

see www.dieselgiant.com for a better explanation of the B-2 piston, and a procedure for fixing if this is indeed the case.

As stupid as it sounds and since it happened on a curve. Take precautions and have a look to make sure the front part of the driveshaft is not turning with the transmission in drive.
It is very unlikely something further back than the transmission let go but never totally impossible. There have been cases of driveshaft welds letting go, Rear ends dropping out suddenly but very unusual on your model, or a cv joint disengaging with not too much fuss. Again highly unlikely just not to be overlooked.