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Date:         Fri, 25 Apr 1997 17:11:52 -0700
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         Paul Uusitalo <puusital@Adobe.COM>
Subject:      Syncro Tire Inflation VS the VC

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


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