The double clutch and/or that push button thing on the gear shifter. Not sure if that’s part of the same system.
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Double clutching is just a way to shift a big truck. Almost all automotive cars that have manual transmissions have what are called synchronizers, they are tapered brass or bronze pieces in between the different gears in the transmission. When you push the clutch in, and move the shift lever, those synchronizers speed up or slow down the gears inside the transmission, so they will sync together, and shift smoothly. A big truck does not have synchronizers, it just has steel sliding collars between the gears. It is up to the driver to speed up or slow down the gears, usually by use of the gas pedal, so those collars will slide together smoothly. When a driver double clutches, they push the clutch in a bit, not all the way to the floor, but just enough to disconnect power from the engine, then they shift to neutral, the let off on the clutch pedal. They then push the clutch again, and slide into the next gear, and let off the pedal. The part in the middle, when they let the clutch out while in neutral is designed to help get all the gears going about the correct speed. The second clutch in is designed to take the force off of everything so they will slide together. By design, double clutching is meant to put the wear into the clutch, a part that is designed to wear out, and is cheaper to replace than the internals of the transmission. Most professional truck drivers do not double clutch, they don’t use the clutch at all, except for stopping and starting. They just feel and float the gears from one gear to the next.
The button or lever on the shift stick is usually a range selector. Big truck transmissions are capable of anywhere from 10 to 18 different gear ratios. In the simplest terms, it’s two transmissions built together. The front half is shifted by the stick, similar to a regular car. The range section is usually one or two or maybe three positions, shifted by the lever or button on the shift stick. For example, when taking off from a stop, a truck will have the range selector in low range, and then will shift 1,2,3,4,5, then will switch the range selector to high range, and shift 1,2,3,4,5 again. Those second set of shifts are actually gears 6-10, but the shift handle moves the same way it did 1-5.
Double clutching is just a way to shift a big truck. Almost all automotive cars that have manual transmissions have what are called synchronizers, they are tapered brass or bronze pieces in between the different gears in the transmission. When you push the clutch in, and move the shift lever, those synchronizers speed up or slow down the gears inside the transmission, so they will sync together, and shift smoothly. A big truck does not have synchronizers, it just has steel sliding collars between the gears. It is up to the driver to speed up or slow down the gears, usually by use of the gas pedal, so those collars will slide together smoothly. When a driver double clutches, they push the clutch in a bit, not all the way to the floor, but just enough to disconnect power from the engine, then they shift to neutral, the let off on the clutch pedal. They then push the clutch again, and slide into the next gear, and let off the pedal. The part in the middle, when they let the clutch out while in neutral is designed to help get all the gears going about the correct speed. The second clutch in is designed to take the force off of everything so they will slide together. By design, double clutching is meant to put the wear into the clutch, a part that is designed to wear out, and is cheaper to replace than the internals of the transmission. Most professional truck drivers do not double clutch, they don’t use the clutch at all, except for stopping and starting. They just feel and float the gears from one gear to the next.
The button or lever on the shift stick is usually a range selector. Big truck transmissions are capable of anywhere from 10 to 18 different gear ratios. In the simplest terms, it’s two transmissions built together. The front half is shifted by the stick, similar to a regular car. The range section is usually one or two or maybe three positions, shifted by the lever or button on the shift stick. For example, when taking off from a stop, a truck will have the range selector in low range, and then will shift 1,2,3,4,5, then will switch the range selector to high range, and shift 1,2,3,4,5 again. Those second set of shifts are actually gears 6-10, but the shift handle moves the same way it did 1-5.
The two parts you describe are separate things, but both related to the drivetrain of a vehicle.
Double clutching is a technique used to change gears. With some heavy duty or older gearboxes, the gears are not synchronised – what this means is that before you are able to select the next gear, the engine needs to be running at the right revs for that gear at the current road speed before it will slot in smoothly. Get the speed wrong and your gearbox will make some horrible grinding noises instead.
So what a driver will do is to use the clutch twice per shift. Once to take the vehicle out of gear and into neutral, where they can use the accelerator to increase or decrease the engines revs to suit the next gear, then use the clutch a second time to move the gearbox into the new gear.
This is one of those techniques that sounds a bit awkward at first, but quickly becomes second nature as you gain experience.
With a modern, manual gearbox car on the other hand, they use what is called a synchromesh gearbox. This is a gearbox that uses specially designed and shaped gears to allow you to shift into a new gear even if the engine is at the slightly wrong speed – you may feel a lurch as a mismatch in gearing and speed is forced to align together, but it works and allows for slightly less precision on the driver’s part.
The extra button or gearstick you see in trucks is gearbox related, but something different. At its simplest, it is basically an extra half step gear you can engage and disengage as needed.
With a normal petrol powered car, the engine will work reasonably efficiently over a fairly large range. With larger diesel powered commercial vehicles however, the rev range the engine will run efficiently over is much, much smaller. The result of this is that you need more gears to allow you to split the range of normal driving speeds over much narrower bands. The more gears in a gearbox, the more complex and expensive it gets, so trucks often use a two gearbox system.
One gearbox will be fairly normal, with around 5/6 gears. The second will only have two gears, but the jump between them will only be about half of a normal gear. By combining the two you double the amount of gears, so instead of changing between gears 1-2-3-4-5 like in a normal five speed car, they combine the two and use both gearboxes to change 1-1.5-2-2.5-3-3.5 and so on.
Exactly how necessary these will be will depend on the gearbox, the load and the road a truck is driving on – fully loaded they may need every single gear, while empty the truck might be light enough to allow them to skip some steps.
The two parts you describe are separate things, but both related to the drivetrain of a vehicle.
Double clutching is a technique used to change gears. With some heavy duty or older gearboxes, the gears are not synchronised – what this means is that before you are able to select the next gear, the engine needs to be running at the right revs for that gear at the current road speed before it will slot in smoothly. Get the speed wrong and your gearbox will make some horrible grinding noises instead.
So what a driver will do is to use the clutch twice per shift. Once to take the vehicle out of gear and into neutral, where they can use the accelerator to increase or decrease the engines revs to suit the next gear, then use the clutch a second time to move the gearbox into the new gear.
This is one of those techniques that sounds a bit awkward at first, but quickly becomes second nature as you gain experience.
With a modern, manual gearbox car on the other hand, they use what is called a synchromesh gearbox. This is a gearbox that uses specially designed and shaped gears to allow you to shift into a new gear even if the engine is at the slightly wrong speed – you may feel a lurch as a mismatch in gearing and speed is forced to align together, but it works and allows for slightly less precision on the driver’s part.
The extra button or gearstick you see in trucks is gearbox related, but something different. At its simplest, it is basically an extra half step gear you can engage and disengage as needed.
With a normal petrol powered car, the engine will work reasonably efficiently over a fairly large range. With larger diesel powered commercial vehicles however, the rev range the engine will run efficiently over is much, much smaller. The result of this is that you need more gears to allow you to split the range of normal driving speeds over much narrower bands. The more gears in a gearbox, the more complex and expensive it gets, so trucks often use a two gearbox system.
One gearbox will be fairly normal, with around 5/6 gears. The second will only have two gears, but the jump between them will only be about half of a normal gear. By combining the two you double the amount of gears, so instead of changing between gears 1-2-3-4-5 like in a normal five speed car, they combine the two and use both gearboxes to change 1-1.5-2-2.5-3-3.5 and so on.
Exactly how necessary these will be will depend on the gearbox, the load and the road a truck is driving on – fully loaded they may need every single gear, while empty the truck might be light enough to allow them to skip some steps.
When I started out as a new trucker back in 1996, I was told to not use the clutch. Clutches get worn out and are expensive, so I always floated the gears. If you do it right, there’s no harm to the transmission, and over the years, it saves your knee.
When I started out as a new trucker back in 1996, I was told to not use the clutch. Clutches get worn out and are expensive, so I always floated the gears. If you do it right, there’s no harm to the transmission, and over the years, it saves your knee.
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