Date: Fri, 2 Jul 1999 23:55:43 -0700
Reply-To: Brent Christensen <bpchristensen@MINDSPRING.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Brent Christensen <bpchristensen@MINDSPRING.COM>
Subject: Re: Turning when hot
There was a recent post from Derek Drew about different VC fluids being used
here in the US (more viscous). Could this possibly account for what we over
here consider "normal" operation? My mechanic has replaced several VC's and
works on dozens of Vanagons, and swears that my VC is fine, even though it
"chirps" in tight turns.
I don't disagree that this is undesirable, since it indicates excessive
activity on the part of the VC, I guess I am just making a point about what
is "normal"...
I'm looking forward to checking into this new VC "rebuild" mentioned by
Derek... :-)
Brent Christensen
'89 Syncro Westy "Klaus"
'95 Cherokee Sport
----- Original Message -----
From: Dr. Rainer Woitok <woitok@RRZE.UNI-ERLANGEN.DE>
Sent: Friday, June 25, 1999 3:32 AM
Subject: Re: Turning when hot
> 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"
>
> ----------------------------------------------------------------------
> | 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 |
> ----------------------------------------------------------------------
>
| 
