Date:         Mon, 10 Feb 1997 19:00:03 -0800
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         bayer@sybase.com (David Bayer)
Subject:      Re: <Syncro> viscous coupling fluid !

>| However it all seems very simple to me.  A Viscous Coupling is a COUPLING,
>| not a differential.  A DIFFERENTIAL PROVIDES SLIP UNDER LOAD (ie cornering)
>| A VISCOUS COUPLING LOCKS UP UNDER LOAD AND provides SLIP under NORMAL
>| CONDITIONS.  The two are completely opposite.

	Well, since I was the one that started it this time, I would like
to clarify what I was talking about. I didn't mean replace the diff with
a VC, but instead to couple the two. The VC transmit load with a threshold
is past; in the Syncro, we are looking at a temperature/pressure threshold
that is an inherit properity of the silicone fluid used. What creates the
heat is the friction within the silicone liquid as two plates start spinning
at unequal rates. If I understand the VC correctly, there are no mechincal
"connections" when the silicone is a liquid, the two disks are allowed to
turn, one driven by a connection to the engine, the other by the front wheels
as they are turned by the ground as the car is moved forward by the rear
drive wheel. When the back wheels slip, the plate powered by the main
driveshaft starts spinning much faster than the plate driven front wheels,
and the VC locks up (now I am not sure how this works, whether the silicone
actually fills some gap between the plates and transmits the power from the
enigne across itself or if it merely pushes some gears together).
	All very nice, but the specifics of how the VC works can be left
aside in this case, because all I want is the locking up action when the
two sides spin at greater than 6% difference. Maybe my idea/dream was not
clear its first iteration. I do not want to replace the diff with a VC, but
instead add a VC across the two output shafts of the diff itself so that
when either of the two output shafts were to spin at greater than 6% of
the other, it would lock up and ineffect, lock the differential. I cannot see
where this could be a problem on a vanagon, maybe the VC should lock up at
somewhere about a 25% difference in speed or something (have to be careful
not to get the difference great enough to snap components when the silicone
fluid solidifies though I guess). Still I do not see why one could not
join the VC concept with a differential to provide an automatic locking diff.

	But I am not the right type of engineer to attempt this. Nor do
I have access to a machine shop to fabricate the pieces. So it will remain
a pipe dream (unless someone hands it to some off road race design team and
they for some reason implement one and give me a second as a favor for
daydreaming ;) ). What did interest me was hearing that the VC could be
replaced with one of those neat pull buttons to make it locking (well, it
was not offered here, I know that, so an order from I guess Austria would
be necessary, but hey, I would have three knobs and all three green dots
would light up when I had true AWD right?).
	To be serious, has anyone looked into importing one/a set of these?
Locking front diff and transfer box? Looking at the current setup, I would
expect the one change needed would be a different front final drive.
Anyone started this research? If I ever get some free time, it would be
something I would persue...

dave