Are Semi Truck Transmissions Synchronized? (Answered!)

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Gearboxes with synchronized transmissions ensure that the gear revolves, mesh, and locks the shaft. It helps drivers lock into the gears without having any issues.

Synchronized Transmissions are not commonly found in semi-trucks in the United States; however, they are commonly found in European trucks. They may be expensive to maintain, but they make driving easier.

Transmission synchronization helps equalize the engine’s speed to the speed the next gear needs. This makes changing gears faster, easier, and smoother.

Without a synchronized transmission, a driver will have to use a rev-matching technique or a double clutch with every gear change to match the speed with that of the engine and the gearbox.

Do Semi-Truck Transmissions have Synchronization?

Most semi-trucks lack a synchronized transmission. However, there are reasons for this. One of the reasons why semi trucks lack synchronized transmission is that they need heavy-duty transmissions.

Heavy-duty transmissions require large parts, even more significant than those used in constructing car transmissions. An average semi-truck has a 10-speed gearbox, while some have more gears.

This is another reason why most semi-truck transmissions are not synchronized. From these two reasons, it can be deduced that the transmission of a semi-truck is more significant, heavier, and has more moving parts than the transmission of a regular car.

Also, the Synchronization of semi trucks adds more moving parts to the gearbox. This makes the gearbox more susceptible to breakage, and this compromises its reliability.

Synchronizing the semi-truck gearbox will make it bigger, making its vehicle positioning more awkward. However, some of the recently built semi-trucks have synchronized transmissions, as modern technology has helped create synchronized transmissions that fit perfectly in a semi-truck.

Most of their semi trucks now have an automated transmission. Although some are found in the USA, they are not as common in Europe.

Benefits of Semi Synchronized Transmissions

Benefits of Semi Trucks with Synchronized Transmissions

There are several benefits of semi trucks that have synchronized transmissions. Some of them are;

  • It makes the truck easier to drive
  • It allows a smoother and easier gear-changing process
  • It reduces the workload on drivers
  • It helps the driver focus more on the road and observe their environment.
  • It reduces the rate of semi-truck accidents.

Disadvantages of Semi Trucks with Synchronized Transmissions

Like every other thing, synchronized transmissions also have disadvantages despite their benefits. Below are some disadvantages of having a synchronized transmission in your semi-truck.

  • It is expensive to build
  • It is a very complex system.
  • It contains more moving parts than the unsynchronized system, which makes it susceptible to damage.
  • Experts can only do its maintenance; hence, the maintenance cost is high.
unsynchronized transmissions

How Does Synchronized Gear Work in Semi-Truck Transmission?

Synchronized transmission gears are complex and have more moving parts than unsynchronized ones.

This is because Synchronization has a vital role to play. It needs to be able to match the speed of the engine with that required for the next gear.

It also allows for a smooth gear change by preparing the following gear for activation. However, the process employed in doing this is quite intricate and complicated. A synchronized semi-truck transmission results in faster and smoother gear changes, making the semi-truck easy to ride.

The Difference Between Synchronized and Unsynchronized Transmissions

There are several differences between synchronized and unsynchronized transmissions. Some of these differences shall be discussed in this part of the article.

The first difference between a synchronized and unsynchronized transmission process is that the synchronized transmission works independently to match the gear speed as you change it. However, the unsynchronized system requires the driver to manually drive to keep up with the change in speed.

Also, the synchronized transmission system is susceptible to damage as it has several other moving parts that the unsynchronized transmission system lacks. Hence, the synchronized system damages quickly, while the unsynchronized system resists damage.

Another significant difference between the synchronized transmission system and the unsynchronized transmission system is that the synchronized transmission system enables drivers to use the gearbox easily and drive without stress. In contrast, the opposite is true of the unsynchronized transmission system.

Synchronized Vs Unsynchronized Transmissions

How Easy is it to Drive a Semi-Truck with No Synchronized Transmission?

Driving a semi-truck is typically not an easy task. This is because of the heavy nature of the vehicle; therefore, it needs more concentration and strength to operate it properly.

Although a semi-truck is a bit difficult to drive regularly, a semi-truck with a synchronized gearbox will be easier. Although synchronized, these semi trucks will still have a stiff clutch pedal; they do not need specialized driving skills like the unsynchronized ones.

The main advantage of semi trucks with synchronized transmissions is that the driver of the semi-truck will be able to pay more attention to the road and observe their surroundings.

How do you drive a semi-truck that does not have a synchronized transmission?

The reason for Synchronization is to make driving the semi-truck easy. Now, semi trucks without synchronized transmissions will be challenging to navigate.

The semi truck’s driver must take over the process without a system matching the engine’s speed to the next gear.

This can only be done using specialized driving techniques when driving a truck with no synchronized transmission. To do this, you need to have years of practice and skill.

The primary technique that will be used in this case is double clutching. Double clutching is done manually to sync the gears.

The process involves clutching two times in a shift. The clutch pedal will be pressed down while the gear will be neutral. Then, the clutch will be released.

Doing this will make the gearbox neutralize the speed of the drive shaft. Then, the clutch will be pressed again, and the transmission will be changed to the next gear before the clutch is rereleased.

Although this technique serves the purpose of synchronized transmissions, it is highly stressful for drivers and can be tiring. Semi-trucks use a heavy-duty clutch, meaning the pedal is difficult to press down.

The Revving method is another method that can be used in place of the synchronized transmission. Revving involves pressing down the clutch and disengaging it when shifting the gear.

Before leaving the pedal to engage the clutch again, the driver revs the engine to bring up the speed and match it to that required for the next gear.

How many miles can synchronize transmission in semi-trucks last?

Semi-trucks with synchronized transmission can generally last long. However, this is relative and depends on the driver’s driving style. With a driver who has smooth control when changing gears and is generally good at driving, a synchronized transmission can last up to 60,000 miles in a semi-truck.

On the other hand, if the driver is aggressive and does not have smooth control over changing gears, the synchronized transmission may get damaged quickly. Due to the delicate synchronized transmission, it can quickly become damaged after about 10,000 miles.

How do you know that your semi truck has a bad synchronized transmission?

As stated earlier, synchronized transmission is a delicate system; therefore, it can get damaged easily if handled improperly. A bad synchronized transmission will make you almost unable to drive your semi truck.

Here are some ways to know when you have a terrible synchronized transmission. Your semi truck needs maintenance services if;

  • You find out that the gears of your semi-truck are regularly grinding despite the clutch being used properly.
  • If the transmission pops out of gear and struggles to get back in, you must take your semi truck to the maintenance.
Heavy green loaded semi

Can a Semi-Truck with a Bad Synchronized Transmission be Fixed?

Yes, a semi-truck with bad synchronized transmission can be fixed. However, based on how complex the system is, it is advised that you take your semi truck to an expert who has knowledge and experience fixing semi trucks with the synchronized transmission.

One of the issues that may occur with the synchronized transmission system may be transmission fluid depletion. Simply refilling the fluid in the transmission can solve this issue.

A dirty transmission system can also contribute to the problem of the semi-truck. The solution to this is to clean the transmission system either by using some cleaning techniques or chemicals.


Not all semi-truck transmissions are synchronized. Although modern semi-trucks have been improved and synchronized, it is still not quite common. A semi-truck with synchronized transmissions is easier to drive, unlike the unsynchronized one.

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