Re: A couple thoughts

[Eliot Lim <eliot@u.washington.edu>]

the clutches are exactly what the name implies: clutches.  they work
by friction surfaces rubbing against each other.  the clutches are
pressed together with hydraulic pistons, which are in turn
electronically controlled, with inputs coming from wheel sensors,
accelerometers and the brake pedal (for deactivation).  without
the electronics, the clutches have no capability of locking.  and
that's the failure mode.  a free unlocked center diff.

the viscous coupling relies on the shearing of a viscous oil by discs
with cutouts to transmit power.  there is usually no contact but they
can be made to rub under extreme conditions if desired.  it is much
much simpler (and dumber) and has nothing in common conceptually with
the clutches.  there are no electronics involved in the heart of the
VC.

maybe you got confused by the diagrams, which do look alike.  if you
doubt jay lamm, how about the official audi v8 factory repair manual and
service training guide?  no contradiction with lamm.


eliot