It is not advisable to drive in 4X4 on hard surfaces for any length of time as there is no center diff in the transmission to account for the build up of transmission bind, this is where the transmission front and rear ends have slightly different rolling ratios due to tyre wear, on dirt this build up in the drive line is released naturally by the slippage created on the loose driving surfaces, on the tarmac it does not release and transmission bind up can result, in severe cases transmission problems can result.
Something I found on line that may help.
 4WD versus AWD
Selector-switches for locking differentials. The leftmost is for center-differential, whereas the two others are for front- and rear-differentials. In the view of some, it is the ability to lock differentials that distinguishes 4WD from AWD. The term four-wheel drive describes truck-like vehicles that may allow the driver to manually switch (sometimes with an automatic option) between two-wheel drive mode (if available) for streets and four-wheel drive mode for low traction conditions such as ice, mud, snow, slippery surfaces, or loose gravel.
All-wheel drive (AWD) is often used to describe a "full time" 4WD that may be used on dry pavement without damaging the differentials, although the term may be abused when marketing a vehicle. AWD can be used on dry pavement because it employs a center differential, which allows each axle to rotate at a different speed. This eliminates driveline binding, wheel hop, and other driveline issues associated with the use of 4WD on dry pavement. For vehicles with more than four wheels, AWD means all wheels drive the vehicle, to varying degrees of engagement, while 4WD means only four of the wheels drive the vehicle continuously. For example, an AWD vehicle with six wheels is often described as a 6x6, the M35 2-1/2 ton cargo truck being one of the best-known examples (dual wheels on the rear axles are not counted as additional drive wheels).
Because all 4 tires in a full time AWD system are connected by a system of differentials, they are more susceptible to torque reduction when a wheel loses traction. Without sophisticated traction control systems, they would become immobilized when any one of the four tires lost traction. A traditional part time 4WD system does not connect the front and rear via a differential, and therefore does not suffer any front/rear torque reduction - if a front tire loses traction, it does not reduce torque delivered to the rear tires, even without traction control systems.
Part time 4WD systems are therefore mechanically simpler, cheaper, and tougher than AWD systems, and inherently better at making use of available traction. Part time 4WD transfer cases are also usually equipped with a gear reduction setting that multiplies torque for greater power at lower speeds, a vital feature for vehicles that will see much off road use. The drawback is that because it lacks a center differential, a part time 4WD system can only be used in low traction situations where the wheels have the ability to slip as needed.
For these reasons, full time AWD is appropriate for improving on road handling and is seen on cars and car based crossover SUVs, while traditional part time 4WD systems without center differentials, or with locking center differentials, are better for heavy duty use, such as off roading or deep snow, and are commonly seen on trucks and truck based SUVs.
Identical drivetrain systems are commonly marketed under different names for upmarket and downmarket branding and, conversely, different drivetrain systems are commonly marketed under the same name for brand uniformity. Audi's quattro, Mercedes-Benz's 4Matic, BMW with the xDrive, Saab's XWD, and Volkswagen's 4motion, for example, can mean either an automatically-engaging "on-demand" system with Borg-Warner ITM 3e magnetic or Haldex Traction hydraulic clutch, or a continuously-operating permanent 4WD system with a Torsen (torque-sensing) or other type of a differential.
Tuesday, February 9th, 2010 AT 2:37 AM