Truck drivers spend a considerable about of time and effort to obtain their commercial driver’s licenses (CDL) and improve their proficiency in operating large freight vehicles. When operating these types of vehicles, they employ various techniques to improve fuel efficiency and safety.
Double clutching is one trucking technique most experienced drivers use when driving manual semi-trucks and involves engaging the clutch twice when shifting gears for a smoother transmission – it’s particularly effective when downshifting.
Double clutching is similar to a regular shift, but the clutch is engaged and disengaged twice. Drivers engage the clutch a first time, shift to the neutral gear, release the clutch, match the engine speed, re-engage the clutch, shift to the desired gear, and then release the clutch again.
Although newer trucks are equipped with automated gear-shift assistance, many truckers continue to operate older vehicles where double clutching is a more common practice.
In this article, we’ll explain what double clutching is and how it works. We’ll also discuss the various benefits it has, such as reduced wear and tear on the truck and improved vehicle control when driving.
How Does Double Clutching Work?
Double clutching involves three components of a manual transmission truck – the clutch, the engine, and the gear. The clutch is an essential mechanical device that links a truck’s engine and transmission.
Upon disengaging, torque is transmitted from the engine, allowing the wheels to move. Similarly, when it engages, it prompts the transmission to disengage from the engine, allowing the wheels to spin independently.
Double clutching is based on the same working principle. The key difference is that the technique matches the engine’s rotation speed with the transmission input shaft before shifting. The synchronization of these working parts ensures a smoother gear shift, particularly when downshifting, and prevents engine grinding and other issues.
When the clutch pedal is engaged, it disrupts the power flow by disengaging the engine from the truck’s transmission. With this disengagement, the transmission’s input shaft can rotate freely while the engine maintains its own rotation.
When the gear is in neutral following the first clutch engagement, the pedal release disconnects the spinning input shaft from the engine. This means that the engine’s rotational speed can be matched with the rotational speed of the transmission.
When shifting into the desired gear, the throttle is engaged to increase the engine’s RPM (revolutions per minute) to generate more power. Once the speed increases, the clutch pedal is engaged the second time to create a disengaged stage between the engine and transmission again.
Finally, the right speed and torque requirement is matched to the driver’s desired gear. Following the release, the vehicle moves smoothly as the moving parts synchronize and match their rotational speeds.
Why Use the Double Clutching Technique?
Regardless of whether your truck is equipped with a synchronizer, every trucker should know how to double clutch. While there are alternatives to double clutching, such as floating gears, none offer the same benefits to truckers. Below, we list some reasons why you should consider using this technique when operating a semi-truck.
It Reduces Wear & Tear of Vehicle Parts
Double clutching synchronizes the engine and transmission rotational speeds, minimizing stress and strain on essential components, including the bearings, gears, and synchronizers.
Double clutching also reduces the overall friction on the engine and transmission and slows down the rate of wear of these components. As a result, truckers can reduce maintenance frequency and costs.
It Allows for Smoother Gear Shifting
It’s common for drivers to experience slight jerks during gear shifts, especially when operating older trucks. Older transmission fluids, faulty valves, and malfunctioning sensors typically cause these issues.
Double clutching is an excellent way to ensure smoother shifting, even if you have synchronizers installed. The technique also allows you to control the inertia produced by the semi-trailer preventing it from pulling back on the tractor and reducing fuel consumption in the process.
It Improves Vehicle Control
Since double clutching improves gear transitions, it can help drivers improve vehicle control, especially when driving on uneven terrain or angled roads that require more frequent gear shifts. The technique also comes in handy when operating trucks in heavy traffic, allowing drivers to maintain stability and improve maneuverability when towing heavy loads.
It Enhances Truck Driver Versatility
Once a truck driver masters double clutching, they can practically operate any type of truck, regardless of its model, condition, or synchronizer installation. Carriers are more likely to hire more versatile drivers, especially if they have a mixed fleet featuring older and newer trucks.
How to Perform a Double Clutch on a Semi-Truck?
Whether you’re new to trucking or used to operating automatic transmission trucks, here’s a simple step-by-step guide on how to double clutch a semi-truck:
- Assuming that you have just started your engine, the first step you will need to take is to step down on your clutch all the way and shift into your first gear and slowly disengage the clutch while stepping on the throttle.
- As the vehicle accelerates, engage the clutch as soon as you want to shift to second gear. As you do so, the transmission and clutch will remain synchronized. However, the engine will continue to rotate independently.
- Next, move the gear lever from first to neutral. All three components (clutch, engine, and transmission) will rotate independently with this move.
- Release the clutch to allow the wheels to rotate independently from the engine. Press on the throttle slightly to increase the RPM and match the engine speed with the transmission speed.
- Finally, re-engage the clutch again and put the truck in second gear. Release the clutch and press on the throttle to accelerate. You can follow the same steps for future gear shifts.
7 Tips for Truckers on Double Clutching
Learning how to double clutch may sound straightforward. However, the practice can take time to master. Here are some tips you can use to improve your double-clutching skills:
- Understand the Advantages: By understanding the benefits of double clutching, you can put theory into practice and help synchronize your engine and transmission speed during gear changes to reduce wear and smoothen gear shifts.
- Practice As You Go: Double clutching is a skill that requires time and continuous practice to master until it eventually becomes a habit. You must be patient and gradually improve your coordination.
- Find the Clutch’s Engagement Point: Every driver has their preference regarding their clutch’s engagement point. Some like to engage earlier to save on fuel, while others prefer a delayed engagement with more room for acceleration. You must practice double clutching with the optimal engagement point regardless of preference.
- Listen to the Engine: Good truck drivers listen to their engine’s sound, especially during gear shifts. With this simple habit, you can get valuable feedback on whether your gear changes are smooth or require adjustments.
- Maintain Your Transmission: Regardless of your truck model, you must regularly inspect and maintain its transmission system. Ensure fluid levels are optimal and there’s no leakage from anywhere. The better care you take of your truck’s transmission and engine, the better performance you can expect from both components.
- Know Your Truck’s RPM Range: Every truck has an optimal RPM range for shifting gears. Make sure you learn about your vehicle’s range to enable smoother transitions.
- Try to Rev-Match: Revolutions matching, also known as rev-matching, is another technique you can master to improve double clutching further when downshifting. It involves reducing the engine speed slightly while the clutch is disengaged to prevent pullback when engaging a lower gear.
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Co-Founder & Writer
About the Author
Andrew is a multi-business owner with over 12 years of experience in the fields of logistics, trucking, manufacturing, operations, training, and education.
Being the co-founder of freightcourse has given him the ability to pursue his desire to educate others on manufacturing and supply chain topics.