Date:         Wed, 20 Sep 1995 13:22:45 -0300
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         smitht@jupiter.sun.csd.unb.ca (Tim Smith)
Subject:      Re: Diff Locking Questions and Trip Report

>needed for locking.  From this, I assume that the central position on the
>dash assembly is for a center differential lock, although I've never even
>seen pictures of this.  One Syncroite on the list (Derek Drew) bought a

The centre lock is 4 small pieces inside the nose of the trans next to the 
output shaft. A sliding collar with splines, a splined stub shaft and a 
shift fork on a shaft. Plus the srevo etc outside! The sliding collar spans 
the splines on the new stub shaft and your existing splined output shaft, 
just slides back and forth for 2/4WD, very neat, could probably be installed 
without even dropping the trans.  You can see about a 1" hole where the vac 
servo goes in, mine drips oil out <grr>, very dirty. No seperate central 
diff like a Jeeps etc. The Syncro system was "designed in" 100% It _looks_ 
like installation is bolt on/in, no machining req'd. All wiring for front 
diff indicator light is in place on mine.

>the manual says to drive straight ahead to make the locker engage after
>pulling the knob, I've found that a slight curve seems to engage it much more
>quickly.  I think that by driving exactly straight, the locking mechanism

Yup, definately, or get stuck and let it engage verrrry gently.

WARNING !!!: reading the rec..4x4 list mention of snapping axles in the 
mighty Hummer. Seems to get their limited slip rear diff to 'lock' up when 
one wheel is airborne you are to use "brake modulation". This requires 
gently pressing the brakes on while applying gas. The airborne wheel drags a 
bit and the wheel with traction gets to push. Slamming on the brakes while 
having one wheel spinning is what breaks the axles, power is transfered to 
the other wheel rapidly and since it has good traction the shafts get 
overtorqued.

  (Note Syncros would never get stuck this way, we always get traction to 
both rear wheels when locked up!) This brake modulation trick works in any 
vehicle with a conventional or "open" diff BTW, Are you listening Tobin? Get 
your parking brake set up to apply even drag on each rear wheel and try it 
out on ice. Better yet, split the parking brake, get a dunebuggy steering 
brake system and lock up the spinning wheel until traction is regained.

WARNING ctd:  It struck me that engaging the rear diff lock with one wheel 
spinning fast and the other stuck would do similiar damage to a Syncro. I 
don't know if the VW system won't engage if wheel spin speeds are greatly 
different, but if they can, then you could snap an axle or CV by engaging 
the lock while bogged. Looking at the engineering drawings of the diff there 
is nothing to prevent this from happening! I use caution, try to engage 
while rolling and swerving gently before it gets messy, preferably with as 
little throttle as possible. Same when unlocking. A new trans/diff is going 
to cost what I paid for the van in the first place. Truly a case where the 
parts are worth more than the whole!

>>     We let the Goodrich AT tires down to 20PSI (I use 40 on the hi-way),
>
>It's been my experience that airing down to 20PSI won't gain you much.  I've
>found that 12-14 PSI seems to help alot.  One rule-of-thumb I've heard is to
>air down until the sidewall height is 1/2 of it's normal height.  This was
>around 12 PSI for my old Bridgestone All-Terrains.  I haven't measured it yet
>on my Goodrich ATs.

Sounds reasonable, my Dad did this for years on Michelin Xs on a Peugeot 404 
wagon. Worked great in winter. These were summer tires, never bought snow 
tires, went skiing every weekend.

Are you using the 14x6 mags or 14x5.5 steel rims for these Goodrich tires? I 
have steel, which is the minimum size for the ATs, 5.5 - 7.0" width spec'd 
by Goodrich. Anyone got a source of cheap 14x6.5 steel rims in VW van bolt 
pattern? 
In that VAG bulletin they say to let the tires down to 4.3 - 5.5 psi in 
sand. This struck me as incredibly low, ie. do you need rim locks to keep 
the tires from spinning on the rims? Lots of warning about rock damage too!

Tim Smith