Double Clutching – A Comprehensive Guide


Double clutching is a driving technique that is only possible in manual transmission vehicles. Truck drivers especially use the technique to make shifting gears more deliberate and smoothly up-shift to accelerate faster. However, if you are new to trucking or just want to learn about double clutching, you can learn more about it here.

Understanding the Truck Mechanism

Planetary gearbox transmission cross section and semi transparent casing

The first thing new truckers should understand before they can start double clutching are the main components that go into driving. The engine, clutch, and transmission are essential components of any truck, and are what help the truck move. The engine powers the vehicle, and the clutch transfers this power to the transmission. The transmission then sends this power to the wheels, making them turn and moving the truck.

Therefore, the clutch is a buffer between the engine and the transmission. It helps regulate the power difference between the engine and the transmission, offering better control over the vehicle. Once the power from these two components better syncs, the vehicle can move smoothly. 

The transmission output shaft’s rotation changes with the vehicle’s gear. Higher gears mean higher rotation and speed, along with less torque. However, the initial gears will always be slower and have less rotation, but will be very high in torque. Remember that the output shaft is the one that sends power to driven wheels. In higher gears, the transmission output shaft spins faster than the engine’s output.

Now that you have a better understanding of how the vehicle’s mechanism works, we can move on to double clutching. 

What is Double Clutching?

Double clutching is a down-shifting technique used by race vehicle drivers and commercial truck drivers. Vehicles with a desynchronized manual transmission might also use this technique. The double clutch isn’t needed in most modern vehicles but is essential for truckers.  

The trucks contain synchronizers, devices that sync the speed between the transmission and the engine. All the components of these vehicles require a similar speed for a smooth driving experience. 

Therefore, double clutching is necessary for a smoother drive while on the road. There are other cases where you might use it too, like when you’re approaching a signal with your vehicle in neutral but the light turns green.  

In this case, shifting your vehicle into the first gear may not be the smoothest option. So instead, you can shift to a higher gear with double clutching. It can also protect your vehicle synchronizers from getting damaged during the process. 

What does double clutching exactly do?

The double clutching primarily helps coordinate speeds between the input and output shafts inside the truck. The fourth gear should be static to avoid jerks and discomfort while driving. It also removes gears connected to the input shaft, granting better control of the vehicle.

How do you Double Clutch? 

Double clutching can be a difficult concept for new truckers or people with little experience in the industry. However, you can consider the following example:

Imagine moving in the fourth gear and needing to slow down to shift into the third gear. It means the engine will shift to a relatively higher RPM rate, so when you press the clutch, the engine continues rotating by itself. However, the clutch and the transmission are now rotating at the same speed.  

You have to move the gear from the fourth gear to neutral before lowering it to the third gear. The clutch and the transmission continue rotating independently.

Double clutching means you need to release the clutch to make the vehicle transition smoothly to the third gear. The clutch will link the engine and the transmission again when you release the clutch, allowing the truck to move forward. 

However, the trucker needs to raise the RPM by pushing down the clutch before they can shift gears. The engine rotation and the clutch increase equal to the third gear (which is still connected to the transmission indirectly). The transmission output shaft matches the speed, allowing for a smoother gear downshift. 

How do you Double Clutch: Quick Step by Step Guide

Understanding double clutching is crucial to ensuring the health of your truck. The truckers need to follow a number of steps for double clutching effectively.

  1. Press in the clutch pedal and limit the output shaft
  2. Place the truck in neutral
  3. Release the clutch slowly and let the truck move forward
  4. Hit the gas lightly
  5. Press in the clutch pedal again
  6. Shift the vehicle into the third gear. 
  7. Release the clutch pedal.

Double Clutching: Further Understanding

Now that we have mentioned the basic concept of double clutching and the steps involved include the synchronizers during this process.

Most modern vehicles have synchronizers which can make the double clutching process obsolete. However, heavy-duty trucks and freight vehicles do not have synchronizers, making it necessary for drivers to learn double clutching.  

The main task of the synchronizers is to synchronize the rotational gear speed (linked to the clutch speed and the transmission speed of the output shaft). 

Therefore, drivers cannot press the clutch twice and directly go to their desired gear. People are looking for a more visual understanding of how double clutching works can check YouTube.

In situations where you will use Double Clutching

Although modern vehicles do not require double clutching, there are several situations where you may still have to use the technique for a smoother ride. Here are the top cases where users may have to utilize the double clutching technique:

  • When truckers want to make a turn without hitting the brakes, they can downshift by double clutching and slowing their vehicles down.
  • In cases where you want to improve and extend the life of your synchronizers.
  • Truckers who want their vehicles to drive over 200,000 miles
  • Truckers driving with a failed clutch linkage can use the double shifting method to drive their vehicle without a problem.

Why do you double Clutch a Semi?

Semi-automatic vehicles have a combination of automatic and manual gearboxes, allowing drivers to choose the gears according to their preferences and then make adjustments accordingly. However, the truckers do not have this option.

The main reason drivers need to double clutch a semi is to extend the life of their gearbox. Shifting the semis without the clutch can cause problems in the gearbox. American Gear Manufacturer’s Association suggests taking vehicles off the truck to avoid mechanical failure. For example, it recommends changing the truck’s oil after the first 500 operational hours, or a total of 4 weeks on average. 

They also recommend learning how to clutch a semi because it can save the vehicle from long-term damage. It becomes a natural part of driving if you spend the time practicing since most truckers don’t even think about double clutching without sufficient practice.

However, learning to double clutch isn’t just about reading guides and watching videos. Some drivers need additional assistance that only professional truck driving schools can provide. This professional training is a must for truckers wishing to ace their CDL skills.

The trucking companies also expect their drivers to know how to double clutch. Learning to double clutch will help truckers save money on gearbox maintenance. The main motto of the trucking industry goes:

“An ounce of prevention is worth a pound of cure.”

How to Double Clutch a Semi

Double clutching a commercial semi-truck can be difficult for some drivers since the gears are wider apart in the RPM speed difference. Thus, shifting the gear from first to second can be challenging. Therefore, drivers cannot shift the gear up like in conventional vehicles. 

Instead, they have to drop the gear down so that the flywheel and the clutch are together for a short period. The RPMs and the rotation speeds of the tires can also match. This way, you can shift to a higher gear on your truck without the scratching or scraping noise.

However, in the case of semi trucks, you cannot change the gear directly. Instead, drivers need to rev the RPM to a certain point to match that of the lower gear, making it a faster revving technique. However, it can be troublesome to if you over-rev the engine and still do not meet the rotation gears of the rear wheels. On the contrary, the difference between the two mechanical rotational gears and rear wheels is still not the same if you under rev. 

To Conclude

Double clutching is nothing short of art if you are new to trucking. It is safe and easy to change your gears without getting jerks or hearing screeching sounds from the gearbox. It is also safe and easy to improve your gearbox health and ensure your truck operates correctly for much longer.

Learning how to double clutch may take time, but it is still worth the trouble as you can eventually develop the muscle memory for it. Truckers should contact a professional trucking school to help them learn double clutching if they still feel like they need assistance.