Car gearbox explained: how it works, the main types and which one your car has

A car gearbox sits between the engine and the driven wheels and matches the engine’s speed and pulling power to the speed you are driving. A low gear gives pulling power to move off, a high gear keeps revs low when cruising. There are six main types, from the manual gearbox to the single fixed ratio of an electric car.

But which one is in your car? “Automatic” tells you surprisingly little. A torque converter automatic, a DSG, a continuously variable automatic and an automated manual all go by that name, and they work in completely different ways. That matters as soon as something feels wrong, because the same jolt or the same flaring revs point to a different cause in each type.

This guide explains how a gearbox works, which types exist, how to tell which one your car has and why that is the first question in any diagnosis. It draws on public sources such as the ANWB (the Dutch motoring association), manufacturer information and our own experience as a transmission specialist. At ATR Transmissies in Montfoort, every complaint starts with the same question: which gearbox is it, exactly?

What is a car gearbox?

The gearbox, also called the transmission, is the part of the drivetrain that carries the engine’s power to the wheels and changes the gear ratio along the way. Every car with a combustion engine has one, whether you change gear yourself or the car does it for you.

In everyday British English, “gearbox” and “transmission” mean the same component. Mechanics and American sources tend to say transmission, while parts catalogues and UK sites usually say gearbox. Sometimes “transmission” or “drivetrain” is used more broadly, and then it also covers the clutch, the differential and the driveshafts. The gearbox is the heart of that chain.

How does a gearbox work?

A gearbox works with pairs of gears of different sizes. Which pair carries the power decides how many times the wheels turn for every turn of the engine.

You know the principle from a bicycle. A small chainring at the front and a large sprocket at the back give lots of force and little speed, ideal for pulling away or climbing a hill. The other way round you get lots of speed for little effort. A car works the same way, except the gears sit in a sealed casing filled with oil.

In a manual gearbox the gear pairs are always in mesh, but the gears spin freely on their shaft. When you change gear, a selector sleeve locks the chosen gear to the shaft. Synchromesh rings, usually made of a brass or bronze alloy, first bring the gear and the shaft to the same speed, so the change is smooth and does not crunch. The gearbox oil lubricates, cools and carries away tiny wear particles so they do not stay trapped between the parts.

An automatic gearbox does the same job but chooses the gear itself. How it does that mechanically differs a lot from one type to the next, which you can read below.

Why does a car need a gearbox?

A combustion engine only produces useful power and torque in a limited rev range. Too few revs and it stalls, too many and it hits the rev limiter. The gearbox keeps the engine in that useful band, from pulling away to motorway speed. That gives a gearbox four main functions:

1. Multiply the engine’s torque at low speed, so the car can pull away and climb.
2. Let the engine run at a sensible speed at higher road speeds.
3. Provide reverse, because the engine only turns one way.
4. Provide neutral, so the engine can run while the car stands still.

What happens if you change gear without the clutch?

In a manual gearbox you usually hear a harsh grinding noise. At that moment the gear and the selector sleeve are turning at different speeds and cannot slide into each other smoothly. A single missed change happens to everyone, but doing it often mainly wears the synchromesh rings faster. Stiff or crunching gear changes are a well-known result.

What are the different types of gearbox?

There are six main types: the manual gearbox, the torque converter automatic, the dual-clutch automatic (DSG or DCT), the continuously variable automatic, the automated manual (also called a semi-automatic or AMT) and the single fixed ratio of an electric car. Full hybrids, from Toyota for example, use a drive system of their own. The main difference is how the gear changes happen.

Manual gearbox

You work the clutch and change gear yourself. The technology is simple and robust, and a manual is usually cheaper to buy. It is less comfortable in stop-start traffic. Passenger cars typically have five or six forward gears and one reverse. You can read separately what the gear lever actually does and how to tell when the clutch is slipping.

Torque converter automatic

The classic automatic has no clutch pedal. A fluid coupling, the torque converter, carries the engine’s power into the gearbox. Planetary gear sets provide the different gears, and hydraulic clutches lock and release parts of those sets to change gear. The result is very smooth shifting. Modern units such as the ZF 8HP have eight or more gears and are controlled electronically. For the full story, see how an automatic gearbox works and our page on the torque converter.

Dual-clutch gearbox: DSG and DCT

A dual-clutch automatic is really two gearboxes in one casing: one for the odd gears and one for the even gears, each with its own clutch. While you drive in third, fourth is already lined up, so the change is extremely fast. DSG is the name the Volkswagen Group uses. Other brands call it DCT, PowerShift or EDC. How it works, which versions exist and what maintenance it needs is on our page about the DSG gearbox and in our explanation of the dual-clutch transmission (DCT).

Continuously variable automatic

A continuously variable automatic has no fixed gears at all. Two cone-shaped pulleys with a steel push belt or chain between them change the ratio gradually, so the engine can stay at an efficient speed. Under hard acceleration the engine can therefore drone at high revs while the speed rises steadily. How this type works, what to watch for in maintenance and which faults are common is on our page about the CVT gearbox.

Automated manual or semi-automatic

This is an ordinary manual gearbox where a computer uses electric or hydraulic actuators to work the clutch and change gear. There is no clutch pedal, but you feel a short interruption in drive at every change, as if someone briefly lifted off the accelerator. Opel Easytronic and Fiat Dualogic are well-known examples. More on our semi-automatic page.

Hybrids: not a conventional gearbox

Toyota and Lexus hybrids use what is often called an e-CVT. The name is misleading, because there is no belt or pulley inside. A planetary gear set splits the power between the petrol engine, a generator and an electric motor, and the electric motors set the effective ratio. It feels stepless to drive, but the hardware is completely different. Some English-language gearbox guides suggest hybrids simply use a normal CVT. They do not, and the difference matters when you are trying to work out a fault. According to the ANWB, the Ford Kuga hybrid works on the same principle. How such a power-split transmission is built is explained on our page about the Ford HF35 eCVT. Not every hybrid works this way, though. The Volkswagen Golf GTE, for example, uses a DSG with an electric motor added, the DQ400e.

Electric cars: a single fixed ratio

An electric motor delivers its torque from standstill and revs far higher than a combustion engine, so changing gear is usually unnecessary. Almost every electric car therefore has a reduction gearbox with one fixed ratio and the differential built in. There are exceptions: the Porsche Taycan has a two-speed gearbox on the rear axle. Read more on does an electric car have a gearbox.

Manual or automatic: which gearbox is best?

No gearbox type is best for everyone. A manual is simpler and usually cheaper, an automatic is more comfortable but technically more complex. Which suits you depends on how and where you drive.

• Manual: simple, robust technology, you choose when to change gear and the purchase price is usually lower. Downside: less comfortable in traffic jams and town driving.
• Torque converter automatic: very smooth shifts. Downside: complex technology, and older units often use more fuel than a manual.
• Dual-clutch: very fast shifts and good efficiency. Downside: pulling away and creeping in traffic can feel jerky.
• Continuously variable: smooth and efficient at steady speeds. Downside: engine drone under hard acceleration, and it is sensitive to the right fluid.
• Automated manual: efficient and mechanically simple. Downside: the short pause at every gear change, especially on older systems.

So the drawbacks of an automatic come mainly from complexity: more parts, more electronics and a greater sensitivity to the condition of the oil. Our view is that the type of gearbox says less than the way it has been maintained. An automatic with well-kept fluid and a calm driving style can last a long time. A gearbox whose oil has never been changed tends to give trouble sooner, whatever the type.

Which gearbox does my car have?

Start with the pedals: three pedals means a manual, two pedals means an automatic or an electric car. The driving behaviour tells you which kind of automatic it probably is. Only the gearbox type code gives you certainty.

• Noticeable but smooth gear changes: probably a torque converter automatic.
• Lightning-fast changes and sometimes a little jerky when creeping: a dual-clutch gearbox.
• Revs that rise and stay put while the speed climbs, with no gear changes at all: a continuously variable automatic, or the e-CVT of a hybrid.
• A short dip in drive at every change: an automated manual.
• No gear changes and no engine noise: an electric car.

The type code is usually on a plate, a sticker or cast into the gearbox casing. The vehicle identification number (VIN) can also show which gearbox was fitted at the factory. Our step-by-step guide is on which automatic gearbox do I have, and for Volkswagen, Audi, SEAT and Skoda on which DSG gearbox do I have. Still not sure? Send us your registration number (your kenteken, if the car is registered in the Netherlands) and we will check.

What are the main parts of a gearbox?

Whatever the type, you find roughly the same building blocks, just built differently:

• Gears and shafts that together form the gear ratios.
• Bearings that support the shafts. Worn bearings cause the familiar humming or whining.
• Synchromesh rings in a manual gearbox, which remove the speed difference before the gear engages.
• Selector forks and sleeves that connect the chosen gear to the shaft.
• Clutch or torque converter, which passes on or interrupts the engine’s power.
• Transmission fluid for lubrication, cooling and carrying away wear particles. Which oil your gearbox needs is explained on our page about gearbox oil.
• Valve body or mechatronic unit in automatics: the valves, sensors and control electronics that manage oil pressure and gear changes, directed by the transmission control unit (TCU).
• Differential, which on most front-wheel-drive cars sits in the same casing.

Why the gearbox type decides what a symptom means

The same symptom can have a different cause in each type of gearbox. That is why at ATR Transmissies we first establish exactly which gearbox it is and measure, before we say anything about the cause or replace any part. Most gearbox guides list symptoms as if every gearbox were the same. This table shows how far apart the possible causes really are.

“My car jerks” is not a diagnosis yet. We read the fault codes first, assess the oil and take the car for a test drive to feel the complaint ourselves. Only then do we give advice, and often a targeted repair is enough instead of a complete gearbox. Continuously variable automatics and automated manuals have their own typical causes again. All the warning signs per symptom, with causes and what you can and cannot still do, are on gearbox failure symptoms. What a fault code can mean is explained on transmission fault codes.

How long does a gearbox last?

There is no fixed mileage. A gearbox is designed to last a long time, and how long it actually lasts depends mostly on the oil, heat and how the car is used.

Dirty or overheated oil speeds up wear on bearings, clutch packs and clutches. Towing a caravan or trailer, lots of short trips and town traffic all put extra load on the gearbox. That applies to automatics too: with timely fluid maintenance and no overheating they last a long time, while an automatic whose oil has never been changed can give trouble sooner.

Many carmakers describe the oil in their automatic gearbox as a lifetime fill. That does not mean changing it is never useful. ZF, the maker of the widely used eight-speed automatic, recommends in the product information for its LifeguardFluid 8 oil a change every 150,000 kilometres, while BMW only mentions replacing the fluid when repairs are carried out. We therefore treat gearbox oil as maintenance, not as a fill for life. Intervals and what a service involves are on gearbox maintenance and changing gearbox oil.

Gearbox trouble? How ATR Transmissies approaches it

We understand that you want certainty about what is wrong with your car before you spend money on a repair. That is why we work in three steps:

1. Book your car in. Send us the registration number, the complaint and any fault codes. We review the request and schedule the car.
2. Independent basic diagnosis. Our transmission specialists investigate where the complaint comes from and take a test drive to experience the problem themselves. You get substantiated advice on the possible next steps. If the cause is in the engine or the clutch rather than the gearbox, we tell you that too.
3. Drive with peace of mind. Based on the diagnosis we discuss what is needed. Once you agree, our specialists get to work. Afterwards we test the car and carry out a thorough final check.

We only repair what is actually needed, and often in a targeted way instead of replacing the whole gearbox. We make some of the parts ourselves and do our own research into materials and tolerances. You can read more about who we are on about ATR (in Dutch). What a repair costs depends on the type of gearbox, the cause and how far the damage has gone. Contact us for a price indication based on your registration number and complaint.

For garages: stuck on a transmission fault? You can book the car in with us or have the diagnosis done remotely with ATR Remote. That way you can keep helping your customer, even when the transmission goes beyond what your own workshop can handle.

Frequently asked questions about car gearboxes

Is a gearbox the same as a transmission?

Yes, in most conversations they mean the same thing: the unit that carries the engine’s power to the wheels and changes the gear ratio. “Gearbox” is the usual British term, “transmission” the usual American one. In a broader sense, transmission can also mean the whole drivetrain, including the clutch, differential and driveshafts.

What gearbox does my car have?

Count the pedals first: three means manual, two means automatic or electric. Then notice how it changes gear, because that points to the type of automatic. For certainty, look for the type code on the gearbox casing or check it via the VIN. We can also look it up from your registration number.

How do you know your gearbox is failing?

Typical signs are stiff or crunching gear changes, a gear that jumps out, jerking, revs that rise without the car speeding up, humming or whining, a burning smell, oil leaks, and a warning light or limp mode. Which causes fit your symptom is explained on gearbox failure symptoms.

Can you still drive with a broken gearbox?

Sometimes, but it is rarely wise. Driving on with a slipping or jerking gearbox can turn limited damage into major damage, for example because wear particles circulate through the oil system. If the car goes into limp mode or you hear metallic noises, have it transported rather than driving it yourself. For automatics with a gear selector warning, see gear selector fault: can I keep driving?

How much does a new gearbox cost?

That depends on the type of gearbox, the make and model, the cause and whether a targeted repair or an overhaul is enough. An overhaul is a very different job from fitting a complete exchange gearbox. The factors are explained on gearbox replacement cost and gearbox overhaul cost. Contact us for a price indication based on your registration number and complaint.

Is replacing a gearbox a big job?

Yes. To remove a gearbox it has to be separated from the engine and lowered out of the car, and on many models the driveshafts or the subframe have to come off as well. Afterwards an automatic often needs fluid filling to the right level and an adaptation. That is exactly why we first check whether a targeted repair solves the problem.

Which is better, CVT or AMT?

It depends on what you value. A continuously variable automatic is smoother, with no gear changes you can feel, but it can drone under hard acceleration and needs the correct fluid. An automated manual is mechanically simpler and efficient, but pauses at every gear change. If smooth town and traffic-jam driving matters most, the CVT has the edge. If you want simple mechanics, the AMT does.

Is an automatic gearbox less reliable than a manual?

An automatic has more parts, especially electronics and hydraulics, so more can wear. With the right oil and timely maintenance a modern automatic still lasts a long time. In our experience, neglected maintenance predicts problems better than the type of gearbox does.

Do electric cars have a gearbox?

Usually not in the usual sense. An electric car almost always has a reduction gearbox with one fixed ratio and a differential, without changing gear. The Porsche Taycan is an exception, with two gears on the rear axle. That reduction gearbox still has bearings, seals and oil, so it can wear too.

In short

A car gearbox matches the engine’s speed and pulling power to your road speed. There are six main types, and four very different designs all hide behind the word “automatic”. Once you know which type your car has, you understand much better what a symptom can mean. Find out what your symptom could mean, or book your car in with ATR Transmissies. We start with an independent basic diagnosis and tell you honestly what is and is not needed.

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