Editing Double-clutching (technique) (section)

==Technique==
In a non-synchromesh gearbox with neutral between gears, a typical shift involves two gear changes, once into neutral, and again into the target gear.<ref>{{cite news |url=https://www.drivingtests.co.nz/resources/how-do-you-change-gears-with-an-18-speed-roadranger-gearbox/ |title=How to change gear with an 18-speed non-synchro gearbox |newspaper=Driving Tests Resources |date=28 June 2021}}</ref> During any shift, disconnecting drive components via a clutch unloads the force from the opposing components from the engine and transmission. Disengaging the clutch for each shift out of, and then into, each gear is double clutching or declutching.<ref>{{cite web |url=http://electronicdesign.com/archive/whats-all-double-clutching-stuff-anyhow |title=What's All This Double-Clutching Stuff, Anyhow?|date=5 August 1993 }}</ref> Due to the absence of a neutral spacing, double-clutching is impossible for sequential gear changes, as with a fully [[sequential manual transmission|sequential gearbox]] used in motorcycles and racecars.

The double-clutching technique involves the following steps:
*The accelerator ([[throttle]]) is released, the [[clutch]] pedal is pressed and the gearbox is shifted into neutral.
*The clutch pedal is then released, and the driver matches the engine speed to the gear speed either using the throttle (accelerator) (when changing to a lower gear) or waiting for the engine speed to decrease (when changing to a higher gear) to a level suitable for shifting into the next gear.
*At the moment when the revs between the input shaft (i.e. engine revs) and gear are closely matched, the driver then presses the clutch again, shifts into the next gear, and releases the clutch. The result should be a smooth gear change.

Although double clutching is a testing requirement when obtaining a [[commercial driver's license]] in some jurisdictions, many truckers learn to shift gears without using the clutch. This is known as [[Float shifting|floating gears or float shifting]], with the clutch needed only during starting and stopping. However, this is not recommended by non-synchro gearbox manufacturers such as [[Eaton Corporation|Eaton]]<ref>{{cite web |url=https://www.youtube.com/watch?v=zL0LX0oo0Mg&t=481s |archive-url=https://ghostarchive.org/varchive/youtube/20211212/zL0LX0oo0Mg |archive-date=2021-12-12 |url-status=live |title=Introduction to professional shifting by Eaton |website=[[YouTube]]}}{{cbignore}}</ref> as it will generally cause additional wear on the gears.

Double clutching can be difficult to master, as it requires the driver to gauge the speed of the vehicle and throttle to the intended gear accurately; vehicle weight and road gradient are important factors as they influence the vehicle's acceleration or deceleration during the shift.

Sometimes, truck drivers use the engine brake to help match the engine speed to the gear. The most common situation is with a loaded vehicle that has no split gears or half gears in the lower range, from gears 1–4. In this case, it is especially difficult and sometimes impossible to get from 1 to 2, and sometimes even from 2 to 3 while starting on a hill. The problem is that by the time the engine speed has dropped sufficiently to enable a shift into the higher gear, the vehicle will have slowed down too much or possibly even stopped, making the shift impossible. The engine brakes, which on some models can be set to different intensities (retarding variable numbers of engine cylinders) enable a shift by dropping the engine speed quickly enough to catch the higher gear before the vehicle has decelerated too much. This technique, sometimes called "jake shifting", requires high skill and much practice shifting without the clutch, and is usually not recommended among truck drivers because mistakes can cause damage to the transmission. According to the National Highway Traffic Safety Administration (NHTSA), municipalities across the United States have banned the use of [[compression-release engine brake]]s, which includes jake shifting, because of noise emission.<ref>{{Cite web |last=Kaminski |first=Janet L. |date=September 22, 2004 |title=Jake Brakes |url=https://www.cga.ct.gov/2004/rpt/2004-r-0741.htm |website=cga.ct.gov}}</ref>