About Truck Transmissions

by Jennifer Garcia

Transmissions are essential in the function of not just trucks, but any vehicle on the road today. Without a transmission, a truck will not shift gears, so it will not go forward or in reverse; it will just sit idle and not move. There are many different kinds of truck transmissions in vehicles today. Some are built for small engines, while some are heavy duty and are built for hauling heavy loads. Regardless of the size, they all perform the same function, which is helping the vehicle stay in motion.

Identification

There are two main types of truck transmissions: manual and automatic. It used to be that trucks only came with manual transmissions, but as automatic transmission became more widely used in vehicle production, trucks manufacturers started including them in their designs to make driving easier.

Types

Manual transmissions must be manipulated by the driver of the vehicle. There is a clutch pedal inside the truck, right next to the brake pedal. In addition, the vehicle also has a shifter, located on the floor of the truck right in front of the dashboard. When shifting, the clutch must be pressed in while simultaneously shifting either up or down, depending on which gear you want to go in. In order to get the truck rolling, the vehicle must be engaged in first gear, and the clutch and gas pedal must be depressed. As the RPMs, or Revolutions Per Minute, climb, the truck is shifted into the next gear by pressing the clutch in. The number of gears depends on the size of the engine. If you have a 4-cylinder engine, it's likely that you will have a 4- or 5-speed transmission, which means it will have 4 or 5 different gears that you can shift into or out of. If you have a 6- or 8-cylinder engine, it's likely that you will have 6 speeds on your manual transmission. The automatic transmission vehicle does not have a clutch--it just has the brake and gas pedals. The transmission shifter can be located on the floor, just like the manual transmission shifter, but it can also be located on the steering column, which is most common in trucks. Automatic transmissions have the following gears: park, drive, reverse, second and third gears. You simply press on the brake pedal and move the shifter into the correct gear and begin driving. As the vehicle rolls down the road and the need to shift arises, the transmission shifts on its own.

Function

The transmission process begins with a shaft that runs from the engine and through the clutch, which is located inside the vehicle. A gear is connected to the shaft in the engine, and together they form a single unit. The clutch functions as a way to disconnect and to connect the transmission and the engine. When the pedal of the clutch is depressed, the transmission and the engine are disconnected. This allows the engine of the truck to keep running even if it is not moving. There is another shaft and set of gears, called a layshaft. The layshaft itself, along with the gears connected to it, also make up a single piece, jut like the clutch shaft and gears do. The clutch shaft and the layshaft are connected by gears, so if the layshaft spins, so does the clutch. When the clutch is engaged, the layshaft gets power from the engine. There is yet another shaft that connects through the differential of the vehicle to the drive shaft. If the wheels of the vehicle spin, this shaft will be spun by gears that sit on bearings. A collar connects the drive shaft to the gears. The collar also has teeth that fit into the holes located on the side of gears. When this happens, the gears are engaged.

Considerations

Truck transmissions can be installed aftermarket, depending on what you intend to use the truck for. If you do a lot of hauling and need a vehicle that will function better in lower gears, the transmission can be taken out and replaced with one that is built for hauling heavy loads. If you do a lot of rock climbing or off-roading, you will most likely need a transmission that has a lower gear ratio, so that you don't constantly have to shift while rock climbing or off-roading; you can simply maneuver the vehicle at a slow and steady pace. In addition, the transmission will need enough torque to be able to pull the vehicle out of pits, over rocks and out of sand traps without getting stuck. You can also purchase trucks with heavy duty transmissions if you intend to use the truck for work. If you haul heavy loads such as trailers, construction materials, etc., you might want to consider a truck with an Allison transmission, which usually comes in General Motors trucks. It provides unparalleled performance and power for heavy work loads. The manufacturing of Allison transmissions began during World War I, and were used to power military vehicles during World War II. After the war, the transmissions were manufactured for the civilian sector and were put in heavy duty vehicles such as buses, delivery trucks and locomotives.

Benefits

Though automatic transmissions are easier to operate, manual transmissions offer unmatched control over the vehicle by allowing you to shift into a higher gear in order to go faster, or downshift into a lower gear in order to gain control and slow the vehicle down without constantly having to use the brakes. This can be handy especially on icy or snow-packed roads.

About the Author

This article was written by the It Still Runs team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information. To submit your questions or ideas, or to simply learn more about It Still Runs, contact us.

Photo Credits

  • photo_camera www.jalopnik.com