Technical Information About the G-Wagen
Why is the G-Wagen the most special 4x4?
1.The Transfer Case:
From 1979 to 1989?? models: Use it when you need more traction. Use the High-Range for more security and for more difficult terrains. Use the Low-Range in low traction areas such as Mud , deep Snow, Hill Climbing so you get a gear reduction when using it, you will then avoid wheel spinning. When using Low-Range you can start at 2nd gear easily . Avoid wide throttle opening when using 1st and 2nd gear (low). What makes it special: The Transfer case in the G is probably the most sophisticated, and is the only Full-Time Synchronised transfer box ever to be made in a 4x4, so that you can pass from 2Wheel Drive to 4wheel-High-range, and EVEN TO LOW-RANGE when the car is still moving, you don't need to completly stop to turn to Low-Range, which is a good point for serious Off-Roading. Only The M-B GELANDEWAGEN provides a synchronised (Shift-0n-the Fly)Low-Range.(Up to W463 97 models??)
From 1989++models:
G-Wagens have improved since 1979, and the newer version have Full-Time permanent 4 wheel drive, so no more 4High to be engaged, only a Low Range is available and still could be engaged on the fly.
2.Differential Locks:
From 1979 to 1989 models:In older models the diff locks are engaged hydraulically with 2 levers. In the new models there are 3 different buttons.
Front diff-lock button, Central diff-lock button, and rear diff-lock button.
The central diff-lock: Comes in the all time 4wheel drive models only, and it makes torque repartition between the front and rear axle equal, this means 50% of power for the front and 50% for the rear axle equivalent to 4High on older models.
Lockers are essential in the G-Wagen. The Gelandewagen was the first 4x4 to have 100% Lockable Diffs(since 1979)
Use them on Low-Traction terrain, such as extreme mud and snow. Pull up the rear diff lock lever and the rear Diff.-Lock is engaged, you must see a red light on your cockpit, when engaged both rear wheels should turn 100% at the same speed. Suppose you have a rear wheel in the air and the other on ground, logically due to the Differential system, the one in the air will spin and the one on the ground provides no traction. When you engage rear Diff Lock , both wheels turn, so the wheel with traction helps you going.
When you use the front diff lock both front wheels turn at the same speed; you'll notice that the steering is becoming harder. You won't be able to turn big curves. Avoid wheel steerings when using front diff lock ( that will damage the differential and/or axles)
3.Suspension:
The suspension in the G-Wagen all models included, is comfortable both on rough terrains, and on-road.
NOTICE: Corrections for these infos are welcomed!!
For more info about the G-Wagens check the following links The Poul Vinther's G-Wagen Page.
This text contains IMPORTANT information about all 4wd systems, including DIFF-LOCKS.
Just as the field of vehicles available with four driven wheels expands yearly, so does the number of different drive systems. And each one is touted as the Best 4wd System. But what do makers mean Insta-Trac, Quadra-Trac, All-Trac or Active-Trac? And does it really make a difference which one you have?
In a word, yes. Perhaps not a large difference, or even one you will notice right off the bat, but there are plenty of subtle distinctions between 4wd systems. Knowing the basics will make you a smarter buyer, not to mention a better driver.
But first we're going to discard 2 common myths. One, 4 wheel drive does not repeal the laws of physics. On slippery surfaces or bad terrain, it will help you get going, might help you turn, but likely won't help you stop. Second, very few production 4-wheel drive vehicles have true 4 wheel-drive-but more on that later.
If you're considering a 4wd, have you weighed the advantages against the costs? A 4wd vehicle offers superior traction, often sits higher providing a better view, could win the neighborhood "My truck is higher than yours" argument, and might be the only way to get the vehicle you want. But generally speaking, the 4wd will cost more to buy(an average of 2000-3000 $ over 2 wheel drive) and to maintain, use more fuel, and require more expensive tires and parts. Then there's insurance, which can be frightfully expensive.
The Systems
Simplifying the field, 4wd systems fall into one of three broad categories: Part time, Full time, and All-wheel drive(awd).
Part time defines a system that normally drives only one axle-usually the rear-but can be changed to drive both axles by moving a lever or operating a switch. In addition part time systems offer Low-range, a gear reduction suitable for steeper grades or low traction surfaces such as mud. Part time systems, like GM's insta-trac, are generally found in pick up trucks and some sport-utilities. While not always as convenient as full time or Awd systems, part time systems are less-complicated, less-expensive, and easier to modify for severe four wheeling.
Full-time systems drive both axles all the time, and share the low-range reduction gearing found in part-time systems, full-time 4wd uses some sort of differential device in the transfer case so it can be used on any surface without binding or winding up the driveline. These are simpler to operate than part-time systems because you don't have to decide when to go into 4wheel drive. It's always engaged. Full-time systems are generally driver tranparent, so you will rarely feel them working, and are found in mid to upper level sport-utilities-Land Rover, Land Cruiser, and Jeep Grand Cherokee V-8, to name a few-and may appear soon in some pickups.
An often unnoticed benefit of most lever-operated part- or full-time systems is the Neutral position for the transfer case. Shiftingthe transfer case to Neutral disconnects the engine and transmission failure, especially when equiped with an automatic.
All-wheel drive systems work much the same way as full-time systems, except that they have no low-range gear reduction. As a result, it's better to think of Awd as as an all-weather system rather than all terrain. An Awd system rarely offers any driver control because it's all automatic. Most often found in cars (Audi quattro, Subaru and minivans) and also shows up on some luxo-SUVs, such as the Ford Explorer V-8 and olds Bravada.
Though strictly speaking not a type of 4-Wheel-drive system, Shift-on-the-fly(SOF) has become a popular feature of 4wd systems. SOF refers to the ability to shift from 2wd to 4wd or vice versa while moving at true road speed. We will use the term only for systems that can be shifted at 50Mph or higher, you will find these limited to certain part time units.
Transfer-Case differentials
The key component in any 4-wheel drive system are the differentials, or their equivalents. As the name implies, a differential allows for a difference between its two sides. In the case of drive systems, the differential allows one driveshaft or tire to rotate faster than the other. This is critical function in vehicles, where the tires on the outside of a turn will travel farther than the tire on the inside of the turn. The difference must be accomodated sommewhere; if the tires can't turn independently, the inside tire will scuff and squeal(bark) as it tries to cover the same distance as the outside tire.
The same diffrential function applies to the front and rear driveshafts, which are driven by the transfer case. If there is no differentiation between the 2 driveshafts speeds, the system will bind (sometimes called driveline windup) on pavement when turning because the front tires travel in a longer arc than the rears. When the system binds, the truck feels like it doesn't want to go anywhere.
An auxiliary gearbox, the transfer case provides power to both axles as well as the reduction gearing for full and part time systems. On minivans and cars, the transfer case is usually integral with the transmission, while on most SUV's and trucks, it is attached to the transmission's output shaft.
In part-time systems, the transfer case connects the front and rear driveshafts directly by gear or chain. But Full-time systems, where the vehicle is used on hard surfaces, must allow some differentiation between the front and rear wheels. The typical full-time systems feature one of four designs: Lockable central differential, Viscous-coupling unit(VCU), electromechanical-coupling unit, or hydraulic-coupling unit.
A lockable center differential runs normally in the open position, letting front and rear axles rotate at their own speeds, and delivering power to the path of less resistance. But this type can be locked-usually mechanically via lever-so that both driveshafts deliver equal power and speed. The Land Rover Defender and Discovery, Hummer, and Jeep Selec-Trac all feature lockable center differentials.
Another design employs a viscous-coupling unit to allow a certain amount of slip between front and rear output shafts. A VCU is a sealed drum filled with a special, thixotropic silicone fluid, and a series of alternating plates, some attached to the units case, some to the driveshafts. This arrangement allows the two parts to turn idependently of one another, at least when there is a little difference in their relative speeds. As one set of plates turns faster than the other, however, the shearing effect increases the viscosity of the silicone fluid, effectively locking two parts together so both driveshafts turn together. VCU also allows differing amounts of torque to go front and rear. The Jeep Quadra-Trac, GM Smartrak, and Range Rover are examples of a VCU system.
Some 4wd systems use a computer-controlled electromechanical clutch, like the clutch paks in an electronic automatic transmission. When the computer detects a difference in driveshaft speed front to rear, it instructs the clutch to engage and limit any wheel slippage. The system does this many times per second, and some even reduce power to the front when cornering. As with VCU's, electronics can vary amount of torque applied to each driveshaft. The Ford Explorer V-6 and Aerostar use this type of system.
Finally the hydraulic coupling unit, like that used by Subaru, uses the same approach as an electromechanical system, except that it uses hydraulic pressure against a series of clutch discs-much like the clutch packs in a conventional automatic-as the medium to reduce wheel slippage.
Axle Differentials
The differential in each axle allows the wheels on opposite sides to turn at different rates. Unfortunately, an open differential sends power through the path of less resistance, so if one tire loses traction, all the torque goes to it - none goes to the wheel with traction. If your vehicle has an open differential in both the front and rear axles- and many do- only one front tire and one rear tire- whichever have the least traction- will get power. That's why most 4wds do not have true 4-Wheel Drive.
Open differentials are easy to work on, have no effect on steering, and have no clutch packs to wear out. They use standard gear lubricating oil.
A limited slip diff (known by many names and designs including Gov-lock, Posi-traction, Torsen, Trac-Lok, etc) limits the speed differential between tires. The mechanical means employed varies by design and manufacturer, but usually involves a cone clutch or a clutch pack (a series of friction discs, some connected to the side gear and others to the case) that permit only a certain amount of slippage to take place between the two tires.
Clutch-pack limited-slip requires a dedicated lubricant which contains a friction modificater. Like the clutch packs themselves, the fluid is subject to wear. Eventually, a limited slip will become an unlimited-slip, at which time the fluid should be changed even if the unit is not rebuilt. In addition, a limited-slip unit in the front axle will effect steering which is why few makers offer them at the front.
The last option in axles is a locking differential. A locking unit, when activated, mechanically locks the left and right axle shafts together and allows no differentiation in their speeds. If one tire is on ice (or off the ground) and the other is on dry pavement, both tires will receive power and turn at the same speed, propelling you more or less, in the direction desired. Locking differentials available on new trucks are normally off, making them behave like open differentials. At the push of a button, they can be locked by electro-mecanichal, pneumatic, or hydraulic power. This should be done only on loose surfaces, and some systems will not engage the locking differentials under certain circumstances. Finally, a locking differential does have an effect on steering, as both front wheels want to go to the same distance. A front locking differential shouldn't be used at any but the slowest speeds.
Only a locking differential in both axles, provides a vehicle with true 4-Wheel drive. Currently, only the Lexus LX450, MERCEDES G-WAGEN, and Toyota Land Cruiser are available with this setup. The aftermarket offers locking differentials for a great many vehicles, but these are better reserved for the experienced or enthusiasts among us.