Just a matter of internal resistance most likely.
Both trans are installed into vehicles, or is his on the bench?
If they are both installed and both cars are off the ground for the test, it means your diff is breaking loose sooner than his.
Out of gear means the output shaft is free to spin while the input shaft doesn't. When installed into the car, the clutch and engine will hold the input shaft still.
Spinning one flange will either make the diff break free and spin the opposite flange the other direction, or the diff will spin as a complete until, and will spin the output shaft with it (the input shaft held by the clutch).
Try this test... put both in 1st gear so the input shaft is held with the clutch, the shafts are connected through 1st gear, and the output shaft will also be held stationary as a result. NOW spin just one flange while both front wheels are in the air.
It'll spin the other flange the opposite direction. The force needed to spin the one flange will show you how tight the diff is before it wants to "break" and transfer power to one wheel or the other.
If the diff is tight, it'll want to turn the engine over. If it is loose, it'll spin easily.![]()



