Question on different types of LSD diffs

[euro3]

OK, so there is the normal open diff (3.73)

Then there's the LSD (S3.73)

The IX has the Visko (3.73V)

And then the IX has the optional Visko Sperre (S3.73V)????

Is the above true? Up until today I though all IX's were locking or LSD. I recently pulled one, when I turn the input shaft both outputs turn at the same time. But, when I removed the output flanges to look at the locking gears I didn't find any???

I'm guessing the the visko is one type of locking set up (fluid) and the sperre is another (gear type). AND, if thats the case, then why would BMW make a Visko Sperre diff? (dual locking?)

Can anyone verify this or explain?

Thanks!

[nando]

ix has many ratios: 3.64 (europe, 5 speed) 3.73 (europe, auto) 3.91 (USA, 5 speed, also no-cat euro models) and 4.10 (USA, Auto)

all use a viscous clutch for locking.

and I don't know what you mean by viscous sperre diff (doesn't mean it don't exist though).