PART ONE - DRIVE TRAIN
TRANSMISSION UPGRADE
Part of the reason why this TriStar was for sale is
because the 3 / 4 gear slider hub was starting to fail. I purchased a
good used AAN gearbox with locking differential and an ADH front locking
differential in Germany with the intention of getting them rebuilt and
reinforced for a TDI motor with at least 50% more torque than the stock
112hp 2.1L motor. The stock 3rd and 4th gears are traditionally weak
and will fail if there is a lot of power applied to the transmission over
time. Perhaps the 112hp motor is the reason for this transmission
failing so quickly? A company in Australia makes stronger (big
teeth!) 3rd and
4th gears with a slightly taller ratio to slow things down at highway
speeds which is perfect for the TDI motor.
|
Final
Drive |
R |
G |
1 |
2 |
3 |
4 |
Original |
34/7 = 4.857 |
6.03 |
6.03 |
34/9 = 3.778 |
33/16 = 2.063 |
49/40 = 1.225 |
41/48 = 0.854 |
Modified |
34/7 = 4.857 |
6.03 |
6.03 |
34/9 = 3.778 |
33/16 = 2.063 |
27/23 = 1.174 |
20/26 = 0.769 |
![](sm3rdgear.jpg)
|
![](sm4thgear.jpg)
|
New and old 3rd
gear. |
New and old 4th
gear. |
I had Darryl at AA Transaxle in Duvall
WA do the transmission rebuild. After meeting Darryl all I can do is
highly recommend him to anyone as he really knows his stuff! His
shop and his work method is highly organized, super clean and very
efficient. My transmission that I gave to Darryl for the rebuild was
starting to show it's signs of age. No serious problems with the
transmission but I got it rebuilt at the right time in it's age before
anything serious happened to it. Cost for the rebuild was $1795 and
$225 per gear set for a total of $2245 USD.
![](sm094onstand.jpg)
|
![](sm094inpieces.jpg)
|
Syncro
Transmission on assembly stand |
Syncro
Transmission in pieces |
DRIVE SHAFT DECOUPLER
A drive shaft decoupler essentially makes the 4WD Syncro into a 2WD when it is in the
open or disengaged mode. I feel this is an important upgrade as it greatly reduces
the wear on the transmission during normal street and highway use where
4WD isn't critical or desirable to have. The decoupler can be engaged by pulling
a knob on the center console that controls a vacuum operated actuator.
This returns the transmission back to it's stock function by letting the
viscous coupler in the front differential decide if it needs to be in 4WD
mode or not. I chose to install a 'sabotaged'
VC that is welded so that it always transfers 100% of the
torque to the front differential when in 4WD mode. This effectively makes our Syncro
into a user selectable 4x4 with user selectable front and rear locking
differentials. When all three knobs are pulled on the dash - all
four wheels have equal power. The only way of getting stuck is to have not enough
traction on all four wheels!
TIRE AND WHEEL UPGRADE
I have chose to run tires
that have a 14% larger diameter than stock. They are the largest
size you can fit on a stock Syncro without doing permanent modifications to the wheel arch
openings, this is important on a TriStar has they come stock with plastic
wheel arches. I am running Continental Sportiva AT in 225/75R16
format on some aftermarket 6.5x16 ET23 alloy
wheels for street originally designed for the Audi A6. These tires are about
74cm (29.2") tall and accomplishes two things for
us. They will give us 10cm more ground clearance and they will
decrease engine RPM by 14% at any given speed as compared to the stock
tires. The slower engine RPMs are important for the TDI motor
because it makes all of it's power below between 2200 and 3800 RPM and redlines at 4400rpm.
UPGRADED SUSPENSION
We have upgraded the suspension for a few
reasons. The 74cm (29.2") tall tires will hit the wheel arches
on a TriStar as it makes the openings smaller. We also want increased ground
clearance as we will be driving down logging roads and other areas that
have suffered from erosion and have deep trenches. The suspension
lift we will be using will take the hub to fender static measurement from
47cm (18.5") to 52cm (20.5"). This lift kit coupled with
the taller tires will increase our overall ground clearance by a very
respectable 15cm (6.0")
As a result of larger and
heavier tires plus an increase in static ground clearance we need to
upgrade our shocks and springs. The larger tires will have a greater unsprung
weight and will require more force to stop the suspension from
moving. Besides having slightly stiffer springs from the lift kit we
also need to have shocks that can restrict movement more than the stock
shocks could. At the rear, we are using Rancho RS9000X
shocks that have adjustable internal valving and about 5cm (2") more
travel than original shocks. At the front we are using nitrogen
gas charged Old Man Emu shocks with 5cm (2") shock and upper control
arm extenders.
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© 2003 -
2004
David Marshall