I know in principle one should always use specialized rollers for that, but those may not be always available. I am aware of two methods: oposite rotating rollers (diff crown remains stationary) and a road test.
I was also wondering if there is a real danger for the Viscomatic, since it might be considered as a non-permanent 4WD system. I understand that with high differential loads between the axles the system might be overloaded (heat, viscous coupling, strain on the panetary gear and the casing, etc.), but it's a viscous coupling on the other hand, so there is no 1-to-1 mechanical gearing to worry about as in some other 4 wheel drive cars (within low speeds the measurements are usually done at, that is).
Yet another issue is, since the rear diff in the Q4 is of the limited slip type, rollers which turn the wheels in opposite direction could potentially damage it, as I suppose.
In my case, I had one brake test done without any special consideration (I had no choice, sadly), and the second one I did was with testing left and right wheel independently, which I am not sure if is helping at all. Luckily, then my 4WD was still most probably disconnected (yet another option would be to pull the fuse and make the car FWD only for the time of the inspection).
What is your experience? I'm sure all of this is valuable and interesting information for everyone.
