Sequential transmission and dual-clutch transmissions both ensure quick and smooth shifting between gears. But their mechanism is different from each other.

Sequential transmissions and DCTs have different applications. They both focus on high-speed shifting, but sequential transmissions prioritize speed above all else. DCTs, on the other hand, are quieter and smoother, allowing them to be used on everyday driven vehicles.  

Both sequential and dual-clutch transmissions allow the driver to select the gear they require without a clutch pedal. They were both designed for performance cars as they considerably saved precious milliseconds during shifting. However, dual-clutch transmissions have found their way to our everyday driving cars over the past few years.

Our car experts explain that both Sequential and DCTs have different applications. Sequentials are more focused on high-speed shifting. They are much lighter than DCTs and are focused only on speed. DCTs, on the other hand, ensure quick and smooth shifting. But they are not as noisy, and they have become more common on vehicles that never hit racetracks.

Sequential Transmission Vs Dual Clutch

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Sequential Transmission

The sequential transmission shares its mechanism with the regular manual transmissions we see on our cars today. This transmission allows the driver to upshift and downshift rapidly, but the gears must be selected in the pre-set order.

There is no option to move directly from one gear to the other without going through the preceding or following gear. For example, if you want to shift from the sixth to third gear on a manual transmission, you will move the shifter from the 6th position to the 3rd position. But on a sequential transmission, you will have to go from 6th to 5th, 4th, and then 3rd.

You might be surprised to learn that it is equipped with a clutch pedal, but racecar drivers only use it to get a good launch and hardly use it for shifting gears after that.

How Does It Work?

There are also some significant differences between manual transmissions and sequential transmissions. The most obvious one is the moving pattern of the shifter. Where the manual transmission uses the conventional H-pattern for the shifter, the sequential transmission’s shifter only moves forwards or backward.

By pulling and pushing the shifter, the driver changes the rotating speed between the input shaft coming from the engine and the output shaft going out to the differential and ultimately to the wheels.

Before we dig into how sequential transmission gets the wheels turning, we need to understand a few technical terms:

  • Dog Clutches use two shafts that rotate at the same speed instead of a set of friction discs on a regular clutch. They comprise small gears that rotate with the output shaft. These clutches require only a brief moment to shift gears, meaning the engine is cut off from the wheel for much less time. Therefore, sequential transmissions do not require clutch pedals.
  • Selector Forks are used to engage the dog clutches into the main gears rotating with the input shafts.
  • Selector Pins are mounted on top of the selector forks and help guide the forks to move in the grooves on the selector shaft.
  • Selector Shaft has all the selector forks mounted to it. It has precise grooves cut into it, which serve as a path for the select pin to travel on. These grooves are engineered to ensure that one gear is engaged at a time.
  • Gear Selector rotates the selector shaft. It is connected to the shifter inside the vehicle.

With the technical terms cleared down, let us look at how the sequential transmission works step-by-step.

  • The car starts in neutral, which means that there is no contact between the input and output shafts of the transmission. The dog clutches are not engaged and sit idle on the output shaft.
  • The driver pushes the shifter in the cabin to engage the first gear. The gear selector rotates, moving the selector shaft and driving the selector pin along the groove, causing the selector fork to move.
  • The selector fork moves and slides the dog clutch along the output shaft into the first gear. Note that the first gear is already connected to and running the input shaft.
  • With the dog clutch securely engaged in the first gear, the output shaft begins to rotate at the speed of the first gear. The power is transmitted from the transmission to the differential and the wheels.
  • When the driver pushes the shifter again, the selector shaft rotates again. The pins move along the groove to move the selector fork, which causes the dog clutch to disconnect from the first gear and almost simultaneously move and engage the second gear. This process continues as the driver keeps pushing the shifter.

Since only one selector shaft moves the dog clutches into the gears, sequential transmissions do not allow the driver to skip gears when shifting. You will have to go through the sequence whether you are upshifting or downshifting.

Benefits of Sequential Transmissions

Sequential transmissions are costly. They are used on high-performance race cars due to the following reasons:

Super-quick shifts

Changing gears on a standard manual transmission is a long process. You depress the clutch pedal, move the shifter into position, and then release the clutch pedal to deliver power to the wheels. Even with advanced techniques like the heel-to-toe method, shifting on a manual transmission can take up to one second.

Sequential transmissions only require the driver to flick a lever or use paddle shifters to change gears much quicker. On the racetrack, even milliseconds can mean the difference between victory and defeat, and sequential transmissions are faster than automatic transmissions and even dual-clutch transmissions.

Lightweight

With fewer components, sequential transmissions are lighter than other transmissions, especially dual-clutch, which have the highest number of components. Weight reduction means better performance on the racetrack.

Dual Clutch Transmission

Dual-clutch transmissions (DCT) are somewhat a combination of manual and automatic transmissions at heart. But we find them more similar to manual transmissions instead of automatics. With a basic understanding of manual transmissions, we will understand how DCTs work.

As the driver presses the clutch pedal on a manual transmission, the clutch engages and disconnects the transmission from the engine. The driver can then use the shifter to select the gear they require and release the clutch pedal to reengage the clutch.

DCTs, as the name implies, use two separate clutches in the transmission but have no clutch pedal. These clutches are controlled electronically and are programmed to engage and disengage automatically, requiring no input from the driver to change the gears, which makes us assume they are like automatic transmissions.  

How Does It Work?

In a DCT, one clutch operates the odd-numbered gears, while the other controls the even-numbered gears. With this arrangement, the transmission can ensure undisturbed transmission of engine power to the wheels.

Unlike the manual transmission that uses one input shaft, a DCT uses two. With impressive engineering, one input shaft runs inside the other. The outer shaft usually controls the even gears, while the inner shaft controls the odd gears.

Both shafts have their own clutch, and that is the secret to lightning quick-shifting, which ensures undisturbed power to the wheels. The DCT can preselect the gear you will be shifting to next and simply switch over without disconnecting the transmission from the engine.

For instance, you are driving in the first gear and accelerating. The DCT can keep the vehicle running in the first gear while simultaneously keeping the second gear engaged using the second clutch. The clutch operating the first gear is disengaged, while the other clutch is engaged.

When it is time for the car to shift into second gear, the transmission will simply engage the odd-number shaft clutch, making that shaft idle and disengage the even-number shaft clutch, causing power to be transmitted from this shaft.

A similar process is followed when downshifting, allowing the car to run in gear while keeping the lower gear engaged.  

Benefits of Dual Clutch Transmissions

Dual-clutch transmissions provide a different driving experience with seamless shifting. Due to the following benefits, they are found on many performance cars and several everyday cars.

Smooth Shifting

These transmissions hardly take more than a few milliseconds to change gears. Advanced electronics shift the gears flawlessly when required. There are no shift shocks, and the accelerations are smooth and continuous.

Improved Efficiency

Dual-clutch transmissions are more fuel-efficient than automatic or manual transmissions. Since the transmission continuously runs without breaks, the power is not wasted or lost during shifting. This ensures a better acceleration experience and also improved fuel efficiency.

Sequential Transmission vs. Dual Clutch

Sequential transmissions are faster than DCTs and better suited for the racetrack than street driving. They are also lighter than DCTs, making them more suitable for performance. However, sequential transmissions are noisy and do not provide smooth shifts. They are also costly.

Dual-clutch transmissions provide swift and smooth shifting and are equipped on many performance cars such as the Acura NSX. They are much quieter and are also well-suited for luxury performance cars.

Overall, we think that sequential transmissions are designed solely for racing. Dual-clutch transmissions, however, can suit a variety of applications like comfort, noise reduction, smooth shifting, and even performance.

About THE AUTHOR

Charles Redding

Charles Redding

I've spent many years selling cars, working with auto detailers, mechanics, dealership service teams, quoting and researching car insurance, modding my own cars, and much more.

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