Date: Sun, 16 May 2004 15:08:34 -0700
Reply-To: David Marshall <vanagon@VOLKSWAGEN.ORG>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Marshall <vanagon@VOLKSWAGEN.ORG>
Subject: Re: Front differential lock with a non-VC Syncro - valve safety
question
In-Reply-To: <Pine.GSO.4.21.0405161314220.11840-100000@oola>
Content-Type: text/plain; charset="us-ascii"
I seldom use the front diff lock - but I use the rear quite a bit. The
Belgium version of the Bombardier/VW Iltis locks front and rear at the same
time - I never could see the logic behind this!
David Marshall
Fast Forward Automotive Inc.
4356 Quesnel-Hixon Road
Quesnel BC Canada V2J 6Z3
http://www.fastforward.ca mailto:sales@fastforward.ca
Phone: (250) 992 7775 FAX: (250) 992 1160
- Vanagon Accessories and Engine Conversions
- Vanagon, Transporter and Iltis Sales and Importation
- European Lighting for most Volkswagen models
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-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com]On Behalf
Of Eric Zeno
Sent: May 16, 2004 10:15 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Front differential lock with a non-VC Syncro - valve safety
question
Dave,
How about haveing one valve control 4wd mode and the other
control both front and rear axle locks?
Eric 86-VW4x4
vw4x4@fyi.net 86-SS Syncro
Pittsburgh, PA USA 1936-Chrysler
92-Jetta GWC
www.fyi.net/~vw4x4/vw4x4.htm
On Sat, 15 May 2004, David Marshall wrote:
> I spent a good hour tonight figuring out the best way to plumb in my front
differential lock on my TriStar. It already has a rear differential lock
and a drive shaft decoupler. For those of you who lack the back ground on
the vacuum controlled differential locks - this is how they work.
>
> There is a control valve that you can pull / push in the cab of the
vehicle has three connections on it. The center connection on the valve has
a constant vacuum that comes from the vacuum reservoir that is in the mid
section of the vehicle next to the drive shaft - this vacuum comes from the
brake booster circuit. Depending on if the valve is pushed in or out will
dictate which of the other two pipes attached to the valve will have a
vacuum. This vacuum will then move a diaphram on vacuum actuator on the
differential lock. This diaphram has a pin attached to it that moves the
mechanism on the inside of the transmission to lock the differential or the
drive shaft decoupler. A very elegant system to say the least.
>
> The original concept that did not have a viscous coupling had a drive
shaft decoupler installed on the transmission. This drive shaft decoupler
was not vacuum operated like drive shaft decouplers you can purchase now.
Instead there was a control cable that went to the decoupler. When you
remove the plastic cover to expose the control valves, it isn't hard to see
that it was designed for only two sets of control valves as there really
isn't that much room there for another set of pipes for a third vacuum
valve. Coming up from the floor is the 'source' vacuum line that goes to a
T and then goes to the center of the two vacuum valves. There isn't enough
room to neatly add a second T for the third valve - not if you want to do it
neatly anyhow. Then I started thinking about a possible 'neatness' solution
to this - even though you would never see the mess behind the plastic cover.
>
> When the drive shaft decoupler is on (putting the vehicle in 4x4 mode)
there will always be a vacuum to the 'on' line that goes to the vacuum
actuator of the decoupler. What I decided to do is make this 'on line' to
the decoupler feed the control valve for the front differential lock so that
it can only be operated when the van is in 4x4 mode. There is a very good
pro and one con to this idea.
>
> On the pro side, driving down the highway in 2WD mode it would be
impossible to turn the front differential lock on by mistake as it would
involve pulling two control valves to make it happen. Turning the front
locker on will make it almost impossible to steer as both front wheels will
turn at the same rate. In order to turn the front locker on, it would HAVE
to be in 4x4 mode.
>
> The con to this is, the only way to turn the front differential lock off
would be to be in 4x4 mode as you would not have a source of vacuum in 2WD
mode. I can't see this being big issue as how would it turn on in 2WD mode
to begin with and you can't accidentally leave it on in 4x4 mode as it is
still quite hard to steer even in the greasy stuff!
>
> As a potential solution to this, I though of perhaps installing a spring
on the vacuum actuator for the front differential lock that will apply
outward pressure on the locking pin, so if vacuum to the actuator is lost,
the force of the spring would make it go in the open position.
>
> Does anyone have any thoughts or ideas on this 'brain wave' of mine?
>
> David Marshall
>
> Fast Forward Automotive Inc.
> 4356 Quesnel-Hixon Road
> Quesnel BC Canada V2J 6Z3
>
> http://www.fastforward.ca mailto:sales@fastforward.ca
> Phone: (250) 992 7775 FAX: (250) 992 1160
>
> - Vanagon Accessories and Engine Conversions
> - Vanagon, Transporter and Iltis Sales and Importation
> - European Lighting for most Volkswagen models
>
>
> Due to the large volume of email we receive, PLEASE include previous
> emails when responding. This will allow us to read the complete dialogue
> in one message and will result in quicker and more accurate responses.
>
