American Truck Simulator – How to Enable Non-Synchro Transmissions

A basic run down on Non-Synchronous (Crash Box) Transmissions, such as the Eaton Fuller Road Ranger, and how to enable their use in American Truck Sim. Keep in mind this feature is still “Experimental”

Non-Synchro? What’s that?

Non-Synchronous transmission, commonly known in the trucking world as a “Crash Box” is one that, as the name suggests, does not use synchromesh gears to match the input speed (Engine RPM) and output speed (Driveshaft Speed). This means that the driver is responsible for matching these two speeds, requiring a lot more concentration and skill in order to deliver a smooth driving experience and prevent damage to the gears. The two ways of achieving this are either by double clutching, or, with some practice, ‘floating the gears’

Why would I want that in my game?

In the real world, many large trucks use Non Sync transmissions, as they are able to withstand large amounts of power and torque, as well as fit more gears into the housing, as the omission of synchro gears means more room for more speeds. Common examples are the Eaton Fuller 13, 15, and 18 speed transmissions, with the latter being very commonplace in the largest of trucks, where the large selection of gears to choose from helps immensely when very heavy weights are being hauled. Enabling these in your game adds an extra layer of realism for those who are chasing that experience, and can help you to appreciate the skill required to haul the deliveries that keep the world turning

How to enable in game

Firstly, if you haven’t already, enable the developer console. Navigate your way to the config file, located in the American Truck Simulator folder in your documents

Right click and open in Notepad or any text editor, and scroll your way down to the command “g_developer” and replace the “0” with a “1”

Next scroll to the command “g_console” , and again replace “0” with “1”

Then, once in game, hit the Tilde Key “~” to open the developer console. Insert the following: uset g_hshifter_synchronized “0”

Don’t forget to change the shifter layout to appropriately suit the transmission in your truck, as well as whatever H-Shifter you may be using (more on this below)

Great job! You’ve done it!


As far as my research has shown, this feature is still somewhat experimental. There are a couple of settings in the controls tab, under “H-Shifter Setup”‘, which according to an old forum reply by Max from SCS software, achieve the following;

  • Shifter Layout Behaviour
    – defines complexity of behaviour. “simple” uses just simple shifting clutch (or clutch-less). “warning sounds” (like gear grinding if you shift on wrong RPM) are telling you are doing something wrong but shift still happens. “advanced” is more real, it won’t let you shift on wrong RPM, but let you handle some additional tricks like eg floating gears (full simulations of input/output transmission shaft, etc) ..
  • Shifter Fast Split
    – IRL for shifting the split you do not need to handle the classical shift with clutch. you set split and when you just hit clutch, gear will be shifted automatically. American trucks can do similar trick with throttle release. this option defines appearance and handling of those fast auto splits.
  • Shifter Toggle Uses Switch Mode (On/Off)
    – This is for shifter devices, where splits are implemented as switches (or hold-buttons) instead of buttons to press.

When I first became aware of this feature and enabled the Non-Sync transmissions many hours ago, I used the console method, but I am not sure if the exact same results are achieved with just the in game settings; It will further investigation. All I can suggest is to play around and find a configuration that works well for you, and you are comfortable and capable in driving. There is no point making the game too frustrating to enjoy. With some time and practice, I have found it quite easy to float the gears, and in my experience it is actually quite difficult to double clutch well. Whether or not this is due to the way the game simulates the behaviour of the transmission or due to my driving style, I am not sure. If you are after a challenge and want to get that step closer to a realistic trucking experience, I recommend enabling the command, and giving it a shot. Find what works for you. Good Luck and Happy Trucking!


Here is a fantastic video by Ian Watson that covers the process of double clutching (The manufactures recommended way to drive, as well as being required by most licensing authorities), as well as briefly touching on floating gears.

Here is a video by carlylea overviewing the process of floating the gears, which is what most truckers will do once comfortable


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