John and others,

On Thu, 1999-06-24 15:01:00 -0400, John wrote:

> ...
> When performing tight turns at low speeds, the rotational speed of the
> front axle will be less than that of the rear axle which should cause
> the viscous coupling to lock. This is normnal.

No, the rotational speed of the front axle will  be greater than that of
the  rear  axle,  and no,   in  this   situation  (different  rotational
velocities caused by  a tight turn at  low  speed) the  viscous coupling
should not lock.

I'm well aware that almost all Syncro drivers agree  that this is normal
behaviour, simply because that's the way their Syncros  are acting.  But
up to now all Syncro drivers who  really replaced their viscous coupling
with  a new one were  amazed at how  easy  going everything suddenly was
(been there, done  that).  With a properly  working viscous coupling and
on a tar sealed  road any slip happens  within the viscous coupling, and
never between tires and road.

> ...
> The "bigger tires" and parking situation could point to a steering wheel
> rotation effort issue. However if his parking difficulties are a lack of
> power assist, that is an entirely different matter which does not
> involve the viscous coupling.

Right.  But  since Steward explicitly mentioned  in his original posting
"differences between wheel speeds" and  that "the locks  are not on",  I
just assumed we were talking about binding of  the viscous coupling here
rather than about power steering problems.

> ...
> However when performing the same type of turn on hot, sticky asphalt,
> the vehicle drivetrain binds and the front wheels "chirp" or jump
> through the turn. I attribute this to a "trapped stress" which develops
> in the four wheel drive system due to the "unforgiving" nature of the
> tire/hot asphalt adhesion. This of course is quite normal and not a
> reason to disconnect the driveshaft and start shopping for a front
> differential (VC) assembly.

No, it's  NOT normal.  Though this  is already in the archives (probably
multiple times)  I'll include here parts  of an  earlier posting from me
about what I've found in the original German VW factory repair manual:

VW's original (German) repair manual doesn't say much  about how to test
the viscous coupling.  They only recommend placing the  rear wheels in a
break testing stand.  If you then switch to  the G-gear (creeping gear),
the front  wheels should move the van  out of the  test stand as soon as
the engine is revving slightly above idle.   If the front wheels fail to
do so the viscous coupling is to be replaced, VW  says.  VW adds another
tiny sentence  to this, saying that only  when the engine  is revving at
idle and with the G-gear  switched in, the viscous  coupling is able  to
absorb all the torque to the front wheels and keep them from moving.

To me  this   last and  rather   ill-formulated (in the  German  manual)
sentence is the key to testing the viscous coupling.   For in most cases
we  are not dealing with viscous  couplings doing less than their share,
but rather with hard-going viscous couplings  which don't have a problem
at all in  moving the van  out  of the  test stand with  the engine just
idling.

Thus the really important thing here is not the van successfully leaving
the test stand.  On the  contrary, the important thing  here is the  van
not moving and staying put in the test stand with the G-gear switched in
and the engine just idling.  If your  Syncro doesn't pass this test your
viscous coupling is probably  worn out and  ready for a replacement.  Or
put  the other way  round: as  long  as your van's  viscous  coupling is
working properly you will not notice your van has got one.

End of the  quote from my   own posting.  Some  ingenious people without
access to a break test stand have modified this test using a floor jack,
but to me this seems a rather risky procedure.  However, the reaction of
the Syncro has to be the same as in a break  test stand: with the engine
just idling and  the transaxle in G-gear the  van must stay put.  If  it
already drags the  floor jack accross your  driveway when idling I'd put
my money on the shot viscous  coupling (litterally :-).  Your milage may
vary.

Sincerely
 Rainer

'89 Caravelle GL Syncro 16"

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