How fast was that 1 wheel spinning? I tested it and also got your results but as soon as you put it in manual and build up a bit of revs the other one will spin too, now its acting almost like a lsd. Its definitely not open.
what about that Bruckell Moonhawk mod the one with the 2.67 Open differential but I think I am going off at a tangent here...
That is a rear diff, we're talking centre diff on awd vehicles. If you go by definition. 4wd refers to vehicles with a locked centre diff (or usually no centre diff at all, usually just a transfer case) and awd vehicles with a centre diff which is not locked (usually limited slip, not always). The d15 states 4wd using a transfer case so should be locked axles and clearly it isn't.
A car with a transfer case can have an open or lockable diff too. The D15 doesnt act like its locked, lsd or open, I dont think the power is literally sent through the prop shafts / drive shafts, the wheels are just coded to act in a certain way.
I went with the definition I found online that a 4wd car has a fixed transfer case. ie: 1 shaft comes from transmission, has a pinion gear on it, a spur gear then has a drive shaft off of either side for front and rear axles. An AWD car has a differential.
Do the driftshafts ingame have any flex or softness in them or do they instantly break as soon as its damaged? i ask because it would be funny to try and drive a car that has a slightly bent driveshaft and have it thrashing around tearing up the undercarriage
They have a certain amount of movement, yes, just like real cars. But I don't think you could make the driveshaft damage the rest of the car, since beams don't have collision. Only nodes do.