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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
Comments: To: Kevin_T._Justice@DADEBEHRING.COM
Comments: cc: vanagon@VANAGON.COM
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"

---------------------------------------------------------------------- | Rainer M Woitok | Phone: (+49-9131) 85-27811,-27031 | | Regionales Rechenzentrum | | | Friedrich-Alexander-Universitaet | Fax : (+49-9131) 30 29 41 | | Martens-Strasse 1 | Telex: d 629 755 tf erl | | D-91058 Erlangen | | | Germany | Mail: Woitok@RRZE.Uni-Erlangen.DE | ----------------------------------------------------------------------


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