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Note added at 6 mins (2011-02-23 08:28:50 GMT)
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http://en.wikipedia.org/wiki/Transfer_case

A transfer case is a part of a four wheel drive system found in four wheel drive and all wheel drive vehicles. The transfer case is connected to the transmission and also to the front and rear axles by means of drive shafts. It is also referred to as a "transfer gearcase", "transfer gearbox","transfer box" or "jockey box" (Australia).

The transfer case may contain one or more sets of low range gears. Low range gears are engaged with a shifter or electronic switch. On many transfer cases, this shifter is the same as the one that selects 2WD or 4WD operation. Low range gears slow down the vehicle and increase the torque available at the axles. Low-range gears are used during slow-speed or extreme off road maneuvers, such as rockcrawling, or when pulling a heavy load. This feature is often absent on all wheel drive sports cars. Some very large vehicles, such as heavy equipment or military trucks, have more than one low-range gear.

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При офроуд машините в режим 4х4 се използва допълнителна предавка за увеличаване на въртящия момент, предаван на колелата и съответно намаляване на скоростта. Това е допълнителна предавателна кутия, с 2 предавателни отношения. В референция 1 са посочени преводни отношения 1:1 (за нормален режим на движение) и 1:2,49 (за тежки режими, при включен режим 4х4). Скоростната кутия е отделна - вж. реф. 2.