Hi Syncronauts,

On Tue, 1998-12-08 16:06:56 -0500, Kevin Justice wrote:

> Has anyone heard of a way to test the viscous coupling in a Syncro?

VW's original (German) repair manual doesn't  say much about how to test
the viscious 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 viscious 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  viscious 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 viscious coupling.  For in most cases
we are not dealing with  viscious couplings doing less than their share,
but rather with hard-going viscious 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
viscious coupling is probably worn out and  ready for a replacement.  Or
put the other way   round: as long as   your van's viscious  coupling is
working properly you will not notice your van has got one.

As  soon   as  you are  encountering   problems with  your  Syncro  when
cornering, in particular after a  long and fast drive, or  as soon as --
despite  of  power steering --  steering   becomes a bit  difficult when
turning and the Syncro slows down considerably when going round a corner
... as soon as one or more of these  things are happening, your viscious
coupling is most probably   due for replacement.   When the  tires start
whining while cornering it might well be already too late ...

I once had all of these symptoms and it was immediately clear to me that
the viscious coupling was the culprit.  But it took some  time for me to
react, and   it took some  more  time for  the  new viscious coupling to
arrive at  my door.  Should you ever  encounter similar problems I would
urge you to immediately get  under your van and  remove the drive  shaft
between  gearbox and front diff.   If you fail  to do this  and wait too
long, severe damage  to the  gearbox and/or  front diff is  the probable
result.  Removing the drive shaft is pretty  straight forward, just four
bolts and nuts (13  mm) on either  end of the  drive shaft.  Then loosen
(just loosen, don't remove them) the three  nuts and bolts (17 mm) which
hold the front diff in place, so the front diff  can move out of the way
a bit  for the  drive  shaft to be   removable.   Don't forget to  again
tighten the 17 mm screws.

When   I was shopping  for  a new viscious    coupling (according to all
reliable sources I contacted  they cannot be  repaired) I  asked several
knowledgable people  how long a  viscious coupling is expected  to last.
Apart from "it depends" (an  employee at Steyr-Daimler-Puch in  Austria,
the firm which was producing the Syncros and  in particular the viscious
couplings for VW)  the answers ranged  from "some 60,000 km" to "between
170,000 and  200,000 km".   Mine was replaced   after 150,000 km  but  I
bought the Syncro with  80,000 km on  the tach  and don't know  for sure
whether  or  not this was still   the first viscious  coupling.  But I'm
assuming it was.

As for the reason  why the silicone  in  the viscious coupling gets  too
stiff   and   starts causing trouble  the    people  I asked unanimously
answered: to much strain.  However,  this is not referring to relentless
off road  driving in groundless mud, but  rather to small  but permanent
differences in rotational speed between front and  rear axle while doing
normal  on road driving.  These  differences in  rotational speed can be
caused  by such things as unequal  tire wear or different tire pressure.
Tire diameters should be the same within a 2  to 4 mm tolerance.  Or, in
other words, if   you're measuring the  depths  of the grooves in   your
tires, the differences should not exceed 1 to 2 mm.

Thus  people not   caring tire pressure   and tire  wear, people  having
mounted  different tire brands on  the front and rear  axles, as well as
people never  routinely using their spare  tire so  it gets worn roughly
the same way as the other tires are most probably ruining their viscious
coupling pretty fast.

As to replacing  the  visious coupling ...  it's more  or less  straight
forward, and I'm assuming the Bentley manual is  covering this.  If not,
get back to me, I've just recently done that and have a  write up of the
procedure in my computer.  It's in German though, but I'm willing to try
to translate  it if anyone  needs it (no,  rest asured, I'm not going to
use  Alta Vista for  translating.   Because if I   did, and if you  then
followed the resulting instructions, your   Syncro would probably  start
dancing on her hind legs :-).

I hope this helps.

Sincerely
 Rainer

'89 Caravelle GL Syncro 16"

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