Gearbox: Definition, Parts or Construction, Working, Types in detail, Function, Purpose, Advantages, Application [Notes & PDF]

Hello reader, In this article we will study Gearbox and it’s sub topic that is Definition, construction, Working, Types in detail, Function, Purpose, Advantages, Disadvantages and Application of Gearbox.

The main objective of the transmission is to deliver high torque at the time of starting, hill climbing, pulling a load, and accelerating. When an object is moving from rest, to meet other resources high torque is required at the driving wheels.

So let’s understand definition of Gear Box,

What is the Definition of a Gearbox?

A device must be authorized to enable the engine crankshaft to revolve at a relatively higher speed, while the wheels turn at a slower speed. This is surrounded by a metal box called a gearbox. The Gearbox is the process of transmitting energy in a mechanical engine to increase the output torque or to change the speed of a motor.

A motor shaft is attached to one end of the gearbox and through the internal gearbox configuration, empowers an output torque and the speed determined by the given ratio.

Parts or Construction of Gearbox:

Gearbox consists of following Main Parts and that are:

  • Clutch Shaft
  • Counter Shaft
  • Main Shaft
  • Bearings and
  • Gears
Main Parts of Gearbox

Clutch Shaft:

A Clutch shaft is also known as a driving shaft, which utilizes the force from the engine and supplies it to the other parts. The driving shaft is attached to them via a clutch, and when the clutch is engaged the driving shaft starts to rotate. 

The clutch gear is provided with a single gear fixed on it and it rotates with the engine speed same as the crankshaft. Point to be noted, both the driving and main shaft are in the same line.

Counter Shaft:

The countershaft is larger as compared to the rest of the three gearboxes. It is provided with numerous gears in variant sizes which can produce a broad level of torque.

Its rotation is different but contributes consecutive speed just like the clutch shaft.

Main Shaft:

Main Shaft is also known as output shafts. It revolves at a different speed and also gives mandatory torque to the vehicles.

The main shaft is splined so gears could move; both engage and disengage in a better way. The neutral gear is the standpoint in which no gear is engaged with the countershaft.


The bearing is elevated on both ends of every shaft. They serve two purposes:

  • It promotes support and
  • Delivers maximum power with less frictional losses. 


Gear is used to transport power from one shaft to another. The quantity of torque transported via gears depends on the number of teeth and size of the gear.

The higher gear ratio produces higher acceleration, and the minor the speed. All the gears are stabilized except the main shaft ones; they can skid into either direction along the shaft.

If the ratio of gear is higher than 1, the car will maintain a higher acceleration and will travel at a higher speed.

Now we will look what is working principle of Gear Box.

Working Principles of Gear Box:

A gearbox consists of gears of varying sizes, because of the different demands in times of the torque needed at the wheels depending upon the road, load, and terrain, for example; climbing vehicles require higher torque than driving on a straight road.

The first gear is larger compared to the other gears, provides maximum torque outcome while generating minimum speed.

The gears vary size from first to the last in decreasing ratio, thus it empowers varying combinations in pulling ability and speed.  

Steps involved in the working of Gearbox:

  • The constant-mesh gearbox includes a drive shaft connected to a gear which is messed with a gear mounted on a layshaft.
  • The layshaft includes various gears, arranged with the gears of the mesh.
  • The gears are not directly linked to the main shaft and can be rotated freely around it.
  • Dog clutches are used to engage the gear and also are splined to the primary shaft, which helps in the rotating process.
  • The Dog clutches are also assigned with the frictional material which helps them to connect with the gear on the main shaft.
  • When the driver pushes the gear stick, the selector fork moves the interconnected dog clutch to engage with a gear.
  • As a result, the clutch and the main shaft rotate with the speed of the gear selected.

Now we will see types in detail,

Types of Gearbox:

There are two main types of Gearbox in an Automobile:

  1. Manual transmission and
  2. Automatic transmission

Manual transmission:

In a manual transmission type of gear system, the driver gets total control and chooses all gear manually operating both a movable gear selector and a driver-operated clutch. This type of transmission is also known as a stick shaft or a standard transmission.

This manual transmission allows the driver to either drop a gear to make the faster process or choose an increased gear to conserve fuel.

Manual Transmission Working Video:

Video credit to Learn Engineering

Here are some of the major types of Manual transmission listed below:

  • Sliding Gear transmission
  • Synchromesh Gearbox
  • Constant Mesh transmission
  • Pre-selector transmission

Sliding Gear transmission:

These gears are found only on older model cars. When the transmission is neutral, the only parts that move within the transmission process are the main gear and the cluster gear. To empower the driving wheels, the clutch pedal should be compressed so that the shifter handle can move.

Sliding Gearbox Transmission

Moving the shifter handle results in changing the position of the shift linkage slides, and forks a gear along the main shaft quickly above the cluster gear.

Once these two gear combines, the clutch can be released.  To change the gears again, drivers need to unleash both the gears before syncing two new gears. 

This type of transmission fails to have the same diameters and tooth numbers, cause the gear to rotate at different speeds and that can result in a gear clash. This is one of the major reasons this gear is no longer used.

Synchromesh Gearbox:

Synchromesh gears are mostly used by modern cars in the gearbox, which synchronizes the rotation of gears that are messed. This type of gear eliminates the risk of gear clashing and makes the shifting process easier.

This gearbox is someway similar to a constant mesh gearbox.

synchronous gearbox

It is provided with synchromesh equipment by which the two gears which are to be engaged are first taken into frictional contact by adjusting their speed and making the process easy.

In major vehicles, the synchromesh mechanisms are not fitted to all the gears, fitted only on top of the gears. In some cases, reverse gears are not provided with synchromesh devices, because they are aimed at engaging when the vehicle is stationary.

When the lever is shifted, the synchromesh cone comes together to meet with a similar cone on the pinion. Due to the result of friction, the rotating pinion is prepared to rotate at the same speed as the synchromesh unit.

For a positive drive additional, movement of the gear lever enables the coupling to override numerous springs, loaded balls and the coupling connects with the dogs on the ride of the pinion. 

The pinion and the synchromesh units start moving at the same speed, as a necessary move before engaging the dog teeth, so that the cones have a better chance to bring the synchroniser and the pinion at equal speed.

Constant Mesh Gearbox:

In this gearbox, all the gears of the main shaft get in constant mesh with the connected gears of the layshaft.

The sliding dog clutch is placed in the middle of the clutch gear, and the second gear, the others are positioned in between the first and the reverse gear. All the gears are independent of the splined main shaft.

Dog clutch skids on the main shaft to rotate with it. All the gear on the layshaft is fixed with it.  When the left-hand dog clutch is brought to skid to the left through the gearshift lever, it messes with the clutch gear, and the upper-speed gear is achieved.

When the left-hand log clutch gets in contact with the second, the second speed gear is achieved. Just like that, by shifting the right-hand dog clutch to the left and right, the first and reverse gear is attained.

In this process, the gears are in constant mesh. They are safer from damage, prevents gear clashing problems, and also don’t produce any unpleasant sound while engaging and disengaging them.

Preselector Transmission:

Manual transmission went through a series of advancements and variations as car manufactures experimented with design.

One of the manual transmissions is the Wilson pre-selector, introduced in 1930 used as a planetary gear system to preselect gear ratios by operating a small lever on the steering section. 

To shift gears, the drivers press the foot pedal that calls up one of the preselected gears, these results in disengaging of the previous gear, and at the same time the new gear engages.

Manual transmission Advantages:

The following advantages of manual transmission is:

  • This is simple in maintenance as they are less complex than automatics, lesser changes occur there to go wrong. The clutch is the only part that requires repair.
  • The fluid is long-lasting and deteriorates less quickly, it requires fewer periodic changes.
  • Automatic gearbox vehicles have a torque converter and hydraulic pump, which causes them to consume more fuel on a more frequent basis. Those who are favorable with the manual transmission, increase fuel economy by 15% and reduces more fuel needs.
  • The braking is better than the Automatic torque converter, which helps in providing more control over vehicles.
  • Its newly brand-new stick shifts are less expensive and cheaper than the automatic counterparts.

Manual transmission Disadvantages:

The following disadvantages of manual transmission is:

  • Those who are new to drive with using a manual gearbox can expert the early few rides to be a bit jerky and stalling while becoming used to the clutch and shift timing.
  • Braking and stopping on a hill can turn out to be both risky and scary since there are chances of getting rolled into traffic or stalled.
  • It requires constant use of the left leg when it comes to driving a stick shift car. It causes the possibility of messing up the leg joints and can result in leg injuries.

Automatic Transmission:

The manual gearbox simply follows the basic principles, but the Automatic transmission is whole on a level altogether.

However the mechanical working going on beneath the surface, any automatic transmission would look friendly to the driver; park, neutral, reverse, and drive, maybe with some extra functions like sports or a manual shift mode. 

The gear lever of the automatic transmission is normally an electronic switch that guides and sends an instruction to the software that manages the gearbox. 

As a result, we have noticed designers choosing to use buttons, dials, or paddles instead of the vintage-style levers for controlling the transmission.

 Now, Types of Automatic Transmission:

The following are the different types of Automatic Transmission:

  • Torque Converter
  • Automated Manual Transmission
  • Dual- Clutch Transmission and
  • Continuous variable Transmission

Torque Converter:

The torque converter is the most common type of gearbox in an automatic transmission, which uses a torque converter to transmit the engine’s rational power to the wheels.

It is a fluid coupling that allows the car to pull away and stop without slowing the engine, though there is some amount of loss in the efficiency as it takes up drive cause of the curved pattern of the turbine blades inward of the converter.

This gearbox helps in the smooth acceleration from low velocities, as well it responses well at low engine revs.

Torque Converter

Automated-Manual Transmission:

It is the type of gearbox, that utilizes a regular clutch and gear configuration, and also uses sensors, actuators, processors, and pneumatic to boost manual gear use.

These types of vehicles are known for jerky engine execution at slow speeds and high acceleration and also it can generate high fuel mileage over a far distance.

Dual-clutch Transmission:

This kind of gearbox is rapidly increasing its demand and it’s the most familiar kind of automatic transmission for petrol and diesel cars.

Most Brands cars such as Volkswagen group brands; VW, SEAT, and Skoda name it a DSG (direct shift gearbox), Audi further calls it S-Tronic and Porsche prefer calling it PDK all are the same thing.

As the name indicates, there are two clutches in action with these gearboxes. In its most original form, these will be two different clutch systems; one for odd and one for even digit gears. 

The gear can perform the pre-select move with the next gear before a shift happens. This indicates the shift to be relatively much faster than with other types of gearbox.

This type of gearbox proposes the same sort of direct feel as a single clutch version but is naturally very efficient and smooth to drive.

It offers less fuel consumption and better performance compared to a manual gearbox. It can be a bit jerky at a slow speed rate, and also can turn out to be slightly clunky when striding between first and reverse gears.

Dual Clutch Transmission

Continuous Variable Transmission:

The Continuous Variable Transmission doesn’t consist of or offers any gears. Rather, it operates cone-shaped with a band around with an axle. The band shifts up and down to vary its length and the gear ratio.

It offers infinite and variable ratios between the upper and lower limit, as a result, it be can be faultlessly optimized for fuel efficiency and performance needs at a given time.

This is more beneficial for hybrid cars, which may use CVT to balance out the work weight between both the petrol engine and electric motor.

The downfall is the driving experience which sometimes may feel bizarre and unpleasant. When it comes to accelerating, it feels the car is jerking against a rubber band.

Also, the unpleasant noise has a horrible buzz because the revs go straight up the peak point and stay there, as the car picks up the speed, instead of rising and falling as working your way through multiple gears.

The coming gearboxes are getting better, so there is a change for CVT drowning.

Video Credit to Kaveh Mad

Automatic transmission Advantages:

Comfort: One of the benefits of using an automatic transmission is its comfort while driving whether it’s short cities or outstation excursions. The clutch offers the pedal-less-operation and the certainty that you don’t have to switch gears manually.

Good Fuel Consumption: Fuel consumption has always been the main point for people opting for an automatic vehicle. There are multiple transmission choices available in the form of AGS (Automatic Gear shift) CVT (Continuously Variable Transmission) and AT (Automatic Transmission) by Maruti Suzuki. Each of these variations of automatic gearboxes has been optimized and coordinated with the Indian driving conditions for favorable balance and fuel efficiency.

Engineering for Versatility and Great performance: Starting with the Auto Gear shaft, In AGC cars you would get more options of shifting between automatic and manual modes. It comes with competent Creep and Kicks-down functions. The Creep down method allows you to dive the car at low speeds in traffic simply by disclosing the brake pedal. The other kick-down feature allows providing instantaneous power and torque for promising velocity.

In Automatic transmission, transmission is relatively responsive to driving inputs. It has a sufficient amount of force to promote instant acceleration and controlled driving performance.

As for CVT, the engines process in greater efficient possibilities to transmit smooth and linear working.  There is also an L mode present which provides driving on inclines, whether it hills, flyovers, or parking lots.

Automatic transmission Disadvantages:

If the automobile is making strange buzzing or wild noises, the torque converter may need improvement or maintenance. This problem with the torque converter can cause a greater level of damage to the transmission.

When the vehicle causes leakage or has low fluid levels, it results in shifting or slipping gears more often. As time passes, it can cause extensive problems for the vehicle. It’s best to instantly change the transmission fluid once the need for it is suspected.

It’s can cause harsh burning smells. If the driver notices a smell burning during performing his drive, he or she should take his car to an equipped professional as soon as possible. Many factors are present to contribute to the overheating of transmission fluid.

Purpose of the Gearbox:

The purpose of Gearbox are follows:

  1. Gearbox facilitates you to control how slow or fast you want to operate your vehicle. Therefore reducing the engine speed that is a ratio of 4:1 in the case of passenger cars and whereas in a greater ratio in case of heavy vehicles like trucks and lorries.
  2. It transmits the torque and engine speed according to its requirements.
  3. Gearbox broadens both the limited speed and torque behavior of an interior combustion engine to a bigger scale.
  4. The Gearbox gives the relative movement between engine and driving wheels due to flexing of the road spring.
  5. It also provides the leverage between the engine and driving wheels to be varied.

Application or Necessity of the Gearbox:

The following application or Necessity of the Gearbox is:

  • To deliver high torque, at the time of turning on the engine, hill climbing, and accelerating.
  • To promote relative movement between the engine and driving wheels.
  • Allows the driving wheels to rotate at a different speed.

Related Resources:


So here we have studied Gearbox in detail. Let me know what else I can help you in this topic or any other topic?. You can check our another articles I am sure that can boost your knowledge. Till than Thank you for reading.

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Er. Amrit Kumar

Amrit Kumar is a Mechanical Engineer and founder of I have done a Diploma and Engineering degree in Mechanical and writes content since 2016.

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