What Are the Different Types of Heavy-Duty Truck Transmissions?

Many people who drive vehicles, either casually or just as part of everyday life, only understand some of the basics of how those vehicles operate. They are just like any other complex technology; they exist to be used, they work until they break, and they can either be repaired by a skilled expert or replaced.

Sometimes, though, it can be beneficial to know a little more than the bare minimum about the vehicles you operate. This can be particularly important for fleet managers, who need to understand the options available for the vehicles they purchase and operate as part of a fleet. Picking a vehicle with substandard capabilities – or a vehicle suited for a different kind of task – can be a waste, either of time and money or of the power and capabilities of the vehicle.

Think of it this way. You wouldn’t buy a heavy-duty dump truck to deliver a couch, right? It’s massively overkill to use such a powerful machine with immense hauling capabilities to move a piece of furniture. Conversely, you wouldn’t want to use a VW Beetle either; it’s too small to carry a couch. Picking the right kind of vehicle for the purposes you have is critical.

What Is the Transmission of a Truck?

One of those elements of a vehicle that many people overlook is the transmission. Many people may know that the transmission is part of the engine and that it’s a critical component, and if it breaks, it’s an expensive repair, but their knowledge may end there. Slightly more knowledgeable people may know that transmissions can be either automatic or manual and that manual transmissions have fallen largely out of favor in recent decades.

For trucks and other fleet vehicles, there’s a lot more to this story. Rather than two kinds of transmissions, trucks have as many as eight different types of transmissions, each with their own pros and cons, and each suited to different purposes.

First, though, what is a transmission?

The transmission is a critical component of an engine. It’s the complex system of gears, clutch, shifter, and computerized elements that transmit power from the engine to the wheels that drive the vehicle.

For a very simple example, consider a bicycle. In a bicycle, the power is delivered by your legs to the pedals. A chain goes to a series of gears, which in turn convert that force into propulsion from the rear wheel. The ability to shift the chain via a derailleur from gear to gear to adjust how much power is transmitted using gearing ratios is the mechanism of a transmission.

In a motor vehicle, the engine uses fuel-air mixtures and sparks to create small, controlled explosions in an array of pistons that turn a crankshaft, delivering rotational force. That force does not go directly to the wheels; if it did, the moment the engine turned over your vehicle would start to move, and there would be no way to control force or speed other than increasing or decreasing the RPM of the engine.

The transmission is a gearbox that encompasses different gearing options, from slower speeds with more torque to higher speeds with less torque to neutral and reverse gears. It also includes the shifting mechanism, which can be manual, automatic, or a combination of the two.

Transmissions are very complex machines that are precision-engineered and designed for smooth operation. Over time, advancements in technology have come up with a variety of different styles of transmission, each of which can be used in different purposes and scenarios.

The Three Main Types of Transmission

At this point, it’s helpful to break down transmissions into three categories. These categories are manual transmissions, automated manual transmissions (also known as AMTs), and automatic transmissions.

Manual transmissions, broadly known as “stick shift” transmissions, have no features to control the shifting on their own. The operator uses a shifter and a clutch pedal to choose the gearing at any given moment. They tend to require more direct skill and knowledge to operate, and improper handling can cause damage to the gearbox.

The primary benefit of a manual transmission is giving the operator direct control over gear selection. Different kinds of manual transmissions offer different granularity of control, but they all function in essentially the same way, allowing the operator to choose the most appropriate gear for a given purpose. This can vary based on load, terrain, road conditions, and more.

The second type of transmission is the automatic transmission. Automatic transmissions are common in most consumer vehicles and many larger, heavy-duty trucks and commercial vehicles today. In automatic vehicles, the transmission is controlled almost entirely by the vehicle’s onboard computer. You may still be able to choose a gear, but for the most part, you simply put the vehicle in drive and let the computer shift for you.

Automatic transmissions function primarily by recording various metrics throughout the vehicle. The engine RPM, the speed and velocity changes of the vehicle as gas or brake are applied, the load, and more, are all calculated and considered by the computerized systems. When you get on a highway and step on the gas, the changes in sound, RPM, and slight lurch are the moments where the vehicle shifts into a higher gear for you to reach a higher speed.

Automatic transmissions lose some of the granularity and control that manual transmissions provide. A driver has to rely on the computer to make the appropriate decision for shifting. This is usually appropriate, but in extreme conditions, such as with very heavy loads, uneven road surfaces, steep hills, and other situations, the computer isn’t programmed to consider those factors and may make inappropriate decisions. Ostensibly, the ability to do basic shifting on your own with an automatic helps alleviate that, but in practice, it’s rarely used.

The third kind of transmission, automated manual transmissions, are a combination of the two. They are meant to address one of the more significant drawbacks of a manual transmission. With a manual transmission, proper timing of shifting and use of the clutch pedal is required for proper shifting. Improper use can cause wear and damage to the clutch and the gearing, which wears it out and makes it harder to shift smoothly until it eventually stops shifting entirely. 

The precision necessary to shift properly requires a not-insignificant amount of experience and timing. Everything from a novice driver to a fatigued driver to a bad day can reduce that precision and cause damage to the transmission. While individual bad shifts won’t ruin a transmission, that damage adds up over time.

The AMT style of transmission is a manual transmission, but instead of using a clutch pedal and a shifter, the driver operates it using an electronic system. This may be controlled with a stick as normal or with paddles or buttons, as seen in some modern electric vehicles, supercars, and, increasingly, trucks. The electronic controls are capable of operating a clutch with microsecond precision, providing a smooth shift with dramatically less possibility of damage. 

The Types and Uses of Truck Transmissions

Each of the three categories of transmission has different types of transmissions based on the configuration of gears and the mechanism of operation. They each have pros and cons and can be better suited to different kinds of operations.

Range Transmissions

Range transmissions are a type of manual transmission and are known as direct transmissions or straight transmissions. Everything you know about a manual transmission generally applies to a range transmission.

They have a limited number of gear ratios and are best used on vehicles where granularity isn’t necessary. Most manual trucks are suited for long-haul applications where shifting is relatively rare, especially when cruising, and where ongoing, consistent operation is best.

Splitter Transmissions

The splitter transmission is a manual transmission similar to a range transmission, but they have a “splitter” lever that allows a driver to differentiate between a higher or lower ratio in a given gear. For a transmission with five gears, it would provide ten levels of granularity, which allows for a greater amount of adaptability in hauling.

These are best suited for cases where starting and stopping are more frequent, a greater variety of speeds and power levels are necessary, and a vehicle needs to adapt to a wider range of loads.

Range-Splitter Transmissions

A third type of transmission combines the two above. They’re effectively an even more granular version of the splitter transmission, with more gearing options and even more versatility.

They are most commonly seen in heavy-duty vehicles with widely variable needs, from slow and heavy hauling to longer cruising and everything in between.

Planetary Automatic Transmissions

Planetary transmissions are a kind of automatic transmission that, while the name suggests something fantastical, are actually the most bog-standard kind of automatic transmission out there.

They are named after a type of gear set called planetary gears, where variations in the gearing ratios can be adjusted easily and within a compact space. They are easy and smooth to use and are one of the most common kinds of transmissions for automatic vehicles.

Dual-Clutch Transmissions

The dual-clutch transmission system is another automatic transmission style. They’re a newer development in transmission technology and feature two clutches that alternate between even and odd-numbered gears. This way, rather than a clutch shifting gears, one clutch engages while the other disengages, providing a smooth and seamless transition between gears. 

They are most useful in trucks that rapidly accelerate and shift frequently, such as when you’re traveling or hauling through hilly terrain, or when you have a very short amount of space to get up to speed. They can be very precise and reduce power loss when shifting, which isn’t very noticeable in the immediate sense, but can add up to operational efficiency over time.

Picking the Right Transmission Type

When purchasing a new fleet vehicle, understanding the transmission type can be a critical component in your decision-making process. In general, you will be balancing several factors:

• Wear and tear on the transmission.
• Comfort and smoothness of operation.
• Fuel efficiency of the transmission.
• Driver training requirements.

Manual transmissions have fine fuel efficiency but are worse for driver comfort and require that the driver know how to operate a manual transmission vehicle, which is a skill many lament is dying out due to the increasing prevalence of automatic transmissions. They also wear out faster due to those training requirements and the natural wear caused by human error.

Automatic transmissions in general have slightly lower fuel efficiency. This may not be relevant in many situations, but in particular for long-haul trucking, it can add up over time. Automatics have lower maintenance requirements than manuals, and are more comfortable for drivers, who don’t need to pay constant attention to gearing and shifting. They also require no real training to learn to use, since it’s all handled for you.

AMTs are better for fuel efficiency than manuals, which can be a powerful boost for long-haul trucking efficiency. Their maintenance costs are also generally lower, though as a newer technology, finding specialists to repair them when they break may be harder. They also offer a driver more comfort, though the training requirement for using them does exist.

AMTs also tend to be the most expensive up-front, with automatics coming in second and manuals third. This is offset by the specialized needs in driver training and in the costs of repairs over time, so it’s a cost to consider.

As far as maintenance goes, you’re in luck. Whatever kind of transmission your vehicles have, we can help. As the operators of a nationwide network of fleet vehicle service centers, we have trained specialists in every kind of transmission from coast to coast. All you need to do is know what transmissions you have (or plan to acquire) and find your nearest service center. Simply reach out, ask if they service the vehicles you plan to use, and set up a maintenance deal right away. We’ll keep your fleet going from the first mile to the millionth.

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