Date: Wed, 9 Dec 1998 14:28:40 +0100
Reply-To: "Dr. Rainer Woitok" <woitok@RRZE.UNI-ERLANGEN.DE>
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: "Dr. Rainer Woitok" <woitok@RRZE.UNI-ERLANGEN.DE>
Organization: RRZE (Regionales Rechenzentrum Erlangen)
Subject: Re: Viscous Coupling Test
In-Reply-To: Msg <852566D4.0074CFBF.00@GGCOMS01.GG.DADEINT.COM> of 1998-12- 8
16:06:56 -0500 from Kevin_T._Justice@DADEBEHRING.COM
Content-Type: text/plain; charset=us-ascii
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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| Rainer M Woitok | Phone: (+49-9131) 85-27811,-27031 |
| Regionales Rechenzentrum | |
| Friedrich-Alexander-Universitaet | Fax : (+49-9131) 30 29 41 |
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