2010 Mercedes GL-Class Owner's Manual - Page 124

122 Differential locks and rear axle differential to improve vehicle traction. The center differential compensates for differences in wheel rotation between the front and rear axle. The rear axle differential compensates differences between the rear wheels. More extreme off-road conditions may call for another solution, engaging a differential lock or preventing the differential from operating altogether. This vehicle comes with two differential locks: transfer case (center) and rear. Each can be engaged simply by operating the rotary switch located on the center console (Y page 123). When the transfer case (center) differential is locked, the combined (or average) speed of the front wheels is identical to the combined rear wheel speed. When the rear differential is locked, both rear wheels turn at the same speed, independent of the individual torque. Please be aware that engaging the differential locks will significantly reduce the steering ability of the vehicle. For your safety and the safety of others and to prevent damage to the vehicle, the differential locks must not be engaged when driving on paved roads. It is important to understand that during on-road/paved driving, differentials are absolutely necessary for providing the essential control and steering ability of the vehicle. The differential locks, therefore, must not be engaged when driving on paved roads and should only be used to the extent necessary to negotiate offroad conditions which cannot be handled by the systems (the 4-ETS, the ESP®, and the transfer case in LOW RANGE mode) this vehicle comes equipped with. Controls in detail i At the front axles, the 4-ETS system compensates for any traction problems. For more information on off-road driving, see "Off-road driving" (Y page 262). A few words about differentials and differential locks When a vehicle negotiates a turn, wheels on the outside of the curve must travel farther and rotate faster than the inside wheels. The differential, the operation of a set of gears that allows the powered wheels in a vehicle to turn at different speeds, makes this essential function possible. The drawback is that the differential also sends most of the engine's power to the wheel with the least load or strain on it. For example, if one of a vehicle's powered wheels sits on a patch of snow and spins because there is no traction, all of the engine's power will go to that wheel because the power will take the path of least resistance. Meanwhile, the opposite wheel, sitting on dry pavement where it could get enough grip to start the vehicle moving, sits idle because it receives no power. The 4-ETS addresses this problem and provides for good control and steering ability by automatically slowing the slipping wheel and thus increasing the power to the other non-slipping drive wheels to get the vehicle moving. The ESP® and the 4-ETS in this vehicle feature such intelligent limited-slip differential technology, ideally suited for onroad and light off-road driving. Transfer case position LOW (Y page 120) also enhances offroad driving capabilities. Switching differential locks ! If the differential locks are engaged, accelerate gently when setting the vehicle in motion. Only operate the vehicle on a single axle dynamometer if the axle not being driven is jacked up or the associated propeller shaft is disconnected. Otherwise the transmission could be damaged.