1981 Ford Fairmont 6cyl auto transmission.
> It is a C4 auto transmission.
>
> I started my vehicle, put it into reverse
> gear, there was a noise like a snap and that was it.
> Looked under the vehicle to see if drive shaft was turning
> when in gear, thinking it might be the differential, however
> the drive shaft does not rotate.
>
> I am assuming it is the transmission or could it be something
> else?
Probably the revese band broke. Nothing to do but have the transmisison rebuilt or replaced, or the whole car towed away to the great Fairmont grave yard.
Ed