As far as most folks are concerned, transmissions operate on the principles of witchcraft and sorcery, consisting of a bunch of gears sloshing around in a bunch of fluid, and moving the car forward when it’s put in Drive.

Inside of a transmission, shafts, gears, cogs, passageways, pumps, bands, clutches and fluid lines are all packed into an incredibly small space, all working to turn the mechanical force generated by your ride’s engine into the miracle of forward momentum.

Transmissions were once simple, low-tech, and about as sophisticated as a pasta salad. Today, with the latest advances and cramming of nine gears or more into a single gearbox, transmissions are incredibly difficult to explain without multiple diagrams, animations and physics lessons. But explain we shall – and below, we’ll take a look at few vital bits of the transmission, some specialty transmissions, and some of your writer’s favourite examples of each.

By time you finish reading our guide, you’ll have a more comprehensive understanding, which will make you more educated, more awesome, and more appealing to the ladies/blokes.

The Gist: Manual or automatic, 5 gears or 10, dual-clutch or manual, a vehicle’s transmission has a simple job. It allows the engine to operate at a fairly narrow range of speeds (RPM) while enabling the vehicle to operate at a much wider range of speeds. The gears used in the transmission help make the best possible use of the engine’s torque, with shorter gears used to take off and accelerate, and taller gears are used to keep the engine revving slowly to save fuel while cruising at speed.

Keep This in Mind: Whatever the sort of transmission we delve into below, remember this simplified fact: a transmission receives power from a shaft connected to the engine, and transmits power to the wheels via another shaft which connects to them.

Manual Shifting: Do you drive a manual? If so, you’re a champ, a boss, and we’d like to buy you a coffee.

Also, your transmission is the easiest to simplify and explain. In simplified terms, one shaft enters the transmission from the engine and is constantly spinning at the same RPM as the engine. Another shaft is connected to the wheels, and always spins at the speed of the vehicle’s wheels.

Gears connect the two shafts to each other, and when one gear on one shaft meshes with one gear on the other shaft, one shaft drives the other, sending the engine’s power to the wheels.

The gears are constantly meshed, but synchronization rings lock different gears into place on the shaft depending on the gear selected. This engages a different gear ratio and either speeds up, or slows down the output shaft. ([With thanks to Blur911 on our forum])

In neutral, the gears aren’t locked in by the syncro rings, – meaning the input shaft and output shaft can spin freely of one another.

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Moving the shift lever controls which sets of gears are engaged with each other, effectively altering the gear ratio in use.

Notable Manuals: Your writer is fond of numerous manual transmissions, key among them belonging to the Mazda MX-5 for its precise, fast-shifting and finely-honed feel, the Porsche Cayman for its springy and smooth action and wrist-flick throw, and the Dodge Challenger SRT8, because of its manly, beefy and heavy-duty feel that’s pure testosterone.

The Clutch: Every transmission needs a method to disconnect it from the engine in certain situations – largely because when vehicles stop, the engine would also stop, or stall, if still connected directly to the wheels.

Manual transmissions use a clutch to connect and disconnect the engine from the transmission. When the driver presses the clutch pedal, the engine and transmission are physically separated. When the driver releases the clutch pedal, he applies the engine’s power to the transmission, and therefore, to the wheels, once more.

As the vehicle is stopping, the clutch needs to be disengaged, separating the engine from the transmission and wheels. If not, the engine will stop when the wheels stop, causing a stall and making you look like a total noob.

A clutch works on the principle of friction: when engaged, the clutch, which is attached to the transmission, clamps solidly to the flywheel, which is attached to the engine. Power is transmitted, and the vehicle is moving.

The Torque Converter: Automatic transmissions need a way to disconnect the engine from the wheels, just like a manual. In an automatic, the torque converter does this job. It occupies the same location in the vehicle’s driveline as a clutch, and has the same job, though it works in a different way.

A torque converter is a type of fluid coupling which looks like a big metal donut. A rotating component called the housing is attached to the engine, and therefore spins at engine speed. A component called the turbine is attached to the transmission.

The turbine and housing spin very closely to one another, but never touch. Instead, force is transferred between the two components via a special fluid circulating between them. Imagine you place a bowl full of syrup on a turntable, and place a small dish on top of the liquid in the bowl. When the bowl spins, it imparts a rotating force on the fluid, which turns the smaller dish, too. At some point, the bowl, liquid and dish will spin as a single unit. Same deal.

When the torque converter housing spins fast enough, it transmits a rotational force on the fluid, which in turn, rotates the turbine and sends power to the transmission.

Here’s why there’s no clutch: the fluid inside the torque converter requires a certain rotational force before it effectively binds the turbine and housing, causing them to rotate as a single unit. This rotational force exists only above a certain speed between the turbine and housing. At very low speeds, or when the engine is idling, this force doesn’t exist, and the components can spin freely, preventing a stall.

Planetary Gears: Key in the operation of an automatic transmission are planetary gears. In very simple terms, planetary gears consist of several smaller gears rotating around a larger one. An automatic transmission has various sets of planetary gears which vary in size, and can be meshed with each other in various combinations to create various gear ratios.

An automatic transmission’s gear ratios come from selectively engaging and disengaging the sets of planetary gears that are driving the wheels at any time. In any given gear, some of the planetary gears in the transmission are simply idling, while other sets are engaged. By engaging and disengaging specific sets of planetary gears inside of the automatic transmission, the path of the engine’s power through the transmission is changed, as is the gear ratio currently engaged.

The Continually Variable Transmission (CVT): Used by numerous automakers for smoother performance, improved fuel efficiency and a higher degree of refinement, the CVT operates like an automatic, but it does away with pre-set gear ratios and stepped shifting between gears.

The CVT typically has a torque converter, an input shaft from the engine, and an output shaft to the wheels, just like a normal automatic. But, instead of an array of inter-connected planetary gear sets, the CVT creates gear ratios with two pulleys, attached to one another via a steel belt or chain. One pulley is connected to the input shaft from the engine, the other to the output shaft, which connects to the wheels.

The two pulleys inside of this type of transmission do an interesting trick: they can change their diameter. In doing so, the CVT is able to instantly engage a virtually infinite number of gear ratios between an upper and lower limit, by changing its pulley diameters and therefore the effective gear ratio currently in use. Instead of a number of pre-set gears, the CVT’s diameter-shifting chain-linked pulleys allow a nearly infinite number of gear ratios to blend into one another, with no hard transition between ratios.

Noteworthy CVT’s: Key in making best use of CVT technology for refinement, efficiency and driving pleasure is the programming which controls the transmission. Effective tuning of the CVT’s gear ratio strategy against the engine’s power curve lies at the core of every good CVT. Further, to help reduce the strange feel of not shifting gears, which distresses some drivers, many automakers utilize programming that simulates the ‘pause…downshift’ sensation of a regular automatic. Some examples of well set-up CVT transmissions include the Subaru WRX (Lineartronic), Nissan Maxima (Xtronic), and Mitsubishi Outlander.

The Dual Clutch Transmission (DCT): Grab a coffee and a snack, because this one’s a doozy. The Dual-Clutch Transmission (DCT) is marketed under different names by different automakers, though they all work on the same principle to deliver higher performance and fuel efficiency than a conventional automatic or manual. Craziest thing about the DCT? It’s virtually impossible to explain.

In very simple terms, a DCT amounts to two manual transmissions contained within a single housing. Let’s call these two separate transmissions “sub-transmissions”.

One of the sub-transmissions contains the odd-numbered gears, for instance, 1, 3 and 5. The other sub-transmission contains even gears, for instance 2, 4 and 6. Like any other transmission, there’s an input shaft from the engine, and an output shaft, which sends power to the wheels.

But here’s the neat part – each of the sub-transmissions has its own input shaft, meaning there are two input shafts, not one. In a DCT, the input shafts from both of the sub-transmissions fit inside of one another, since one is slightly larger than the other, and hollow. This allows them to operate like a single unit. The nutshell? A DCT basically allows two transmissions to turn from the same input shaft, at the same time.

At the end of the input shafts are two clutches. One is attached to the outer, hollow shaft, the other, to the slightly smaller inner one. Remember – each of these shafts is attached to a different sub-transmission. The clutches, therefore, control which shaft, and therefore, which sub-transmission, is currently driving the wheels. These special clutches are computer controlled, so there’s no clutch pedal to press. There’s also no torque converter, as the clutches open on their own when the vehicle is stopping.

Say you’re accelerating slightly in third gear. The sub-transmission that houses the odd-numbered gears is engaged, in third, and the sub-transmission that houses the even gears is disengaged, but has fourth-gear pre-selected and waiting. Shifting up simply disengages the clutch from the odd-numbered sub-transmission, and simultaneously engages the clutch on the even-number sub-transmission, where fourth gear is ready to go.

This happens in milliseconds. In the process, the outer, hollow input shaft stops spinning, and the inner, thinner one starts spinning, simultaneously. Key word? Simultaneously. This two-in-one input shaft design allows gears to change without any slowing down of the power delivery to the wheels.

So now, cruising along in fourth gear with the even-number sub-transmission engaged, the odd-number sub-transmission pre-selects fifth gear in the meantime, so it’s ready when needed.

Here’s the key: with two sub-transmissions acting on the two-in-one input shaft, an upshift actually just changes the currently-engaged sub-transmission at some point after the gear change has already occurred. Drivers get smoother and faster shifts, and no interruption in power flow.

Notable DCT’s: Common in performance cars, and making their way into the mainstream, there’s no shortage of DCT transmissions in the market. Your writer’s very favourite belongs to the last-generation BMW M3. Advanced controls allow drivers to set gear shift speed and force, with the most aggressive mode changing up at full throttle so fast, it ignites the rear tires upon a full-throttle shift into second gear. Lightning-fast gear changes with beautiful rev-matching are also characteristic of the DCT transmissions used by Porsche, Volkswagen and Audi.

The AMG SpeedShift: This one’s exclusive to Mercedes Benz’s AMG performance division. Dubbed the SpeedShift, it amounts to a conventional automatic transmission, but without a torque converter. Instead, to handle application of engine power to the transmission, a compact clutch system is used. This enables various enhanced performance functions like Race Start (launch control), faster gear changes, and higher overall performance and efficiency.

Importantly, the clutch used on this type of transmission is operated by a computer and actuators, not the driver, so there’s no clutch pedal to press.

By doing away with the comparably inefficient torque converter, which wastes energy as a result of having to drive fluid through various components, the SpeedShift is basically a hybrid transmission with components of both a manual and automatic, combined to offer the best of both worlds. Most notable? This setup does away with the slippage characteristic of a torque-converter, providing the driver with faster, more precise off-the-line responses to throttle inputs. With no fluid to pump, churn and get moving, the SpeedShift transmission feels more direct and instantaneous to its driver.

The Acura 8-Speed DCT: The AMG Speedshift is only one example of a hybrid transmission which blends components from two other types of transmissions. Another was recently launched by Acura – consisting of an 8-speed DCT, with a torque converter. It’s similar to the SpeedShift’s polar opposite: rather than use gears like an automatic with a clutch like a manual, it uses the manual-like gears of a DCT, with a torque converter like an automatic.

Life is all about trade-offs, and though a torque converter wastes some energy because of how it operates, it is a smoother and more refined way to get a car moving off the line. So, says Acura, drivers get smoother performance in stop-and-go traffic, and other situations where using a clutch to get moving is less refined. Drivers get gearshifts at DCT speeds, and DCT levels of efficiency, but with smoother low-speed stops and starts.

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