Editing Unimog (section)

=== Gearbox ===
Traditionally, the Unimog has a [[splitter gearbox]]. Over the years, three different ''base gearbox'' designs have been used, all following the same principle, and having four gears and two ranges (called ''groups'') and an additional direction gear. Those designs were ''UG-1/xx'', ''UG-2/xx'', and ''UG-3/xx''. UG is an abbreviation for ''Unimog-Getriebe (Unimog-Gearbox)'', the number after the slash resembles the input torque in [[Kilopondmetre|kp·m]] (=9.80665&nbsp;N·m).<ref group="N">The kilopondmetre (kp·m) is the traditional technical unit of torque used in many European countries until the early 1980s. It equals the force that a mass of 1 kilogram applies. If the acceleration is exactly 9.80665&nbsp;m·s<sup>&minus;2</sup> (default gravitational acceleration), this equals 9.80665&nbsp;N·m.</ref> Until 1955, the Unimog ''base gearbox'' UG-1 was a constant-mesh countershaft gearbox, it was then upgraded with synchroniser rings to a synchromesh gearbox. However, the synchromesh-version was only used for the [[Unimog 404|404-series]], and the constant-mesh version remained the standard gearbox for the 411-series. In 1957, the synchromesh-version became an option for the 411-series, before it became the standard gearbox for all Unimogs in 1959.<ref name=Vogler_2014 />{{rp|38-39}} The following gearbox versions UG-2 and UG-3 were made as synchromesh versions only.

There are different ''layouts'' of the gearbox, namely ''F-layout'' and ''G-layout'' as well as their upgraded layouts, not having particular names. The F-layout is the original gearbox layout and is limited to the first two gears in the first range as it does not have selector sleeves, meaning that in total there are six forward gears. Instead of a reverse gear, the gearbox has its direction gear, which, in theory, can be used to reverse any gear. Due to the lacking shifting sleeves however, the reverse direction can only be used in the first range, which itself is limited to the first two gears, resulting in only two reverse gears (resulting in six forward and two reverse gears). To operate the gearbox, there is only one shift lever with a six-speed H-layout, the gearbox shifts its ranges automatically. An additional shift lever is used for shifting into reverse. The ''G-layout'' has an additional reduction gearbox, which can be used in all gears. This effectively doubles the number of gears (twelve forward and four reverse gears). This reduction gearbox was also available with an additional crawler gear, which can only be used in the first range (twenty forward and eight reverse gears). As of 1976, shifting sleeves were added and a four-speed-H-layout replaced the six-speed-H-layout, which allows using all gears in all ranges.<ref name="Gearbox">Helmut Schmitz: ''[https://www.unimog-community.de/2012/08/20/getriebevarianten-u-406u-421/ Getriebevarianten U 406/U 421]''. August 20th, 2012. Retrieved May 19th, 2017 (in German)</ref> With the introduction of the UG-3-gearbox, the standard gearbox-shifter-layout was changed to an eight-speed-H-H-layout, with eight gears on one lever, without any additional switches. When shifting from "4th" into "5th" gear, the gearbox automatically shifts into range 2 and back into gear 1. Crawler gearboxes were offered as a factory option for the UG-3 gearbox as well, resulting in 24 gears. The design with the additional direction gear was kept, which means that all 24 gears can also be used in reverse mode. Since the highest final gear ratio allows top speeds of up to 110&nbsp;km/h, and the reverse gear only comes with a small reduction of 1:1.03, the top speed in reverse mode is more than 100&nbsp;km/h. To prevent such high reverse speeds, a lock for the second range was available as a factory option, allowing only the first range (gears "1" to "4") in reverse mode.<ref>Oldtimer Traktor Heft 11-12/2012</ref>