Mastering the Truck Stick Shift: A Driver’s Guide to Gearboxes

For those unfamiliar with the intricacies of heavy-duty vehicles, the world of truck transmissions can seem like a different language. While automatic transmissions have become increasingly common, many trucks, especially those built for demanding tasks, still rely on manual transmissions, often referred to as Truck Stick Shifts. These aren’t your average car manuals; they are complex systems designed to manage immense power and torque. Let’s delve into the fascinating world of truck stick shifts and explore how they operate.

Understanding the 2-Stick 6-Speed Transmission

One common type is the 2-stick, 6-speed transmission. Despite being called a 6-speed, it’s essentially a 5-speed gearbox augmented with an auxiliary section. You’ll notice two gear levers: the main stick and the auxiliary stick.

In typical driving scenarios, you primarily use the main stick, which is located closer to the driver. This stick controls five forward gears, shifted in a conventional 1-2-3-4-5 pattern. During normal operation, the auxiliary gearbox remains in “Direct” mode. Think of this as the standard, everyday driving setting.

However, the auxiliary gearbox comes into play when you need extra grunt, like when hauling very heavy loads or navigating challenging off-road conditions. In these situations, you would engage the auxiliary gearbox into “Low” mode. This effectively acts like a super-low first gear.

Here’s how it works in practice:

1. Starting from a standstill under heavy load or in difficult terrain: Engage the auxiliary gearbox to “Low”.
2. Use the main stick to select 1st gear. This provides maximum torque to get the truck moving.
3. Once the truck is moving and you’re clear of the obstacle or on level ground: Shift the auxiliary gearbox from “Low” back to “Direct”.
4. Resume shifting through the main gearbox as usual: 2nd, 3rd, 4th, and 5th gears.

Essentially, the auxiliary gearbox in “Low” mode splits the first gear, giving you an ultra-low starting gear for demanding situations. The transition from “Low” to “Direct” requires a bit of finesse. It’s best to wait until the truck is on relatively flat ground, allowing the engine RPMs to reach around 1600 before making the shift to ensure a smooth transition. Attempting this shift while still struggling uphill can lead to missed gears due to the rapid drop in road speed.

Exploring the Complexity of Multi-Speed Transmissions: 18 and 20 Speeds

For even greater control and adaptability, especially in long-haul trucking and extreme load conditions, you might encounter transmissions with even more gears, such as 18-speed or 20-speed setups. These are often found in “B model” trucks and utilize a “Quad box” system.

These systems also employ two sticks: a main stick and a compound or auxiliary stick. The main stick, furthest from the driver, typically has 5 forward positions and one reverse. The compound gearbox is where the real magic happens, offering four positions: Low Low, Low Split, Hi Split, and Direct.

The shifting sequence for an 18-speed or 20-speed transmission is more involved:

1. Start in Low Low range with the compound stick and 1st gear on the main stick. This provides the lowest possible gear ratio for starting with extremely heavy loads.
2. Shift through gears 2, 3, 4, and 5 on the main stick while keeping the compound stick in Low Low.
3. To move to the next range, simultaneously move both sticks: Shift the compound stick to Low Split and the main stick back to 1st gear.
4. Again, shift through gears 2, 3, and 4 on the main stick. In Low Split range, 5th gear is typically not used.
5. Repeat the process to enter Hi Split range: Move the compound stick to Hi Split and the main stick back to 1st.
6. Shift through all five gears on the main stick (1-5) in Hi Split range.
7. Finally, shift to Direct range: Move the compound stick to Direct and the main stick back to 1st.
8. Shift through gears 2, 3, and 4 on the main stick. Similar to Low Split, 5th gear is often not used in Direct range in some configurations.

The reason for not using 5th gear in the Low Split and Direct ranges in some 18/20 speed transmissions is often attributed to the gear ratios being too close or the gears spinning too fast, making 5th gear redundant or even detrimental in those ranges.

Mastering the truck stick shift, whether it’s a 6-speed or a more complex multi-speed system, is a skill that requires practice and understanding. It’s a testament to the engineering ingenuity that allows these massive machines to handle the toughest jobs.