With tire pressures set to VW spec, (take your pick from inside the door
jam, I run fronts at 40 and  backs at 48) you must be pretty darn close to
the 3mm F to R tire size difference (Tim describes below) that will cause
the Syncro's viscous coupling to begin to engage, no?

Do you think that the VC/front differential setup is somehow "calibrated"
to deal with the difference in tire diameters as a result of specified
front/rear inflation pressures?

Or perhaps the figures below indicate the sensitivity of the VC system as
designed but not necessarily as actually implemented in production
vehicles?

However, the notion of the VC being "detuned" a bit to enhance its
longevity in the face of inevitable real world situations (slow tire leaks
that you don't notice, mis-alignments, etc) just does not seem like a very
German engineering solution (American yes, German, no).

Or perhaps nobody really took into account this Syncro specific requirement
when they wrote up the inflation reccomendations in the first place (which
for me - as a software tester - is an all too believable scenario), and
we've all been driving around ruining our VCs because we don't have all 4
tires inflated to the exact same pressures.

Any thought on this?

Oh, and by the way, how does one tell when their VC has failed.

Paul Uu

At 6:56 AM -0700 4/21/1997, Tim Smith wrote:
> Couple of test points from a tech paper by VAG.
>
>- braking tests showed up to 23% improvement in stopping distance due to the
>syncro 4WD system over same vehicle in 2WD.
>
>- a difference of greater than ~5 RPM across the coupling will initiate lock
>up process.  Such a difference occurs with 3mm tread wear diff. F to R on
>175/70/13 tires at 160kph. check those tires/pressures folks.
>
>Tom