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Hi Volks,
    I have no syncro and do all my off roading with an 8n ford tractor. But
couldn't ignore the syncro thread any longer. I have no practical knowledge
of syncro except it seems to me they are a pita to work on compared to a
2wd. I have helped pull an engine and a front differential.   I have some vw
service training books from fellow list member David Drew, thanks David.
This is what they have to say about vc and this is  a quote.

    When the speed difference between the two shafts becomes greater than 6
percent , which could happen if the rear wheels lost traction on a road
surface, the outer splined plates connected to the flanged shaft begin to
cut or shear the silicon fluid.  The shearing action of the fluid causes
internal heat and the result is a sharp increase of the fluid's viscosity.
It becomes more difficult for the fluid to become sheared and the coupling
locks up.
    Because of the rapid rise in temperature and pressure, lock-up occurs
very quickly. In about 1/10 second or 1/4 turn of the tire.
    Power is transmitted between the plates with fluid as a medium.

Unquote. The book has a graph that shows the fluid can go from goes from a
minus 30 degrees C to 100 degrees C nearly instantly.  Note.  The flanged
shaft mentioned above is connected to the front differential.
Darrell