Transmissions What They Do and How They Work

When we said that the first thing you should do with your newly financed vehicle is to get to know it, we weren’t joking. If you have a general idea about how your car’s systems work and how they should operate, you’ll be able to tell easily if something’s wrong. Transmissions are one of the most failure-prone systems on a car, thanks to all of the moving parts — so you should know what’s going on down there.

What is a Transmission?

All machines have two basic systems: a power source and a power transmission. The engine is your power source, and every moving part between the engine’s pistons and the wheels are part of the transmission. It literally transmits power from the engine to the target.

Car finance brokers like to think of themselves as the engine that gives power to the consumer when in dealings with a lender. They help drive the transaction and get the customer into their vehicle sooner.

The transmission, also called the drivetrain, includes the clutch, gearbox, differential, drive shafts, and for rear-wheel-drive vehicles, the prop shaft. When you’re driving a manual transmission vehicle, you only really interact with the clutch and gearbox. Consequently, many use the word “transmission” to refer to just the gearbox and the clutch.

Drive Shafts, Prop Shafts, and Differentials

The shafts, drive and propeller or “prop” are both, mechanically speaking, the same thing: a shaft with gears that transmits torque from one component to another. The difference is that drive shafts run perpendicular to the main axis of the car, connecting the wheels directly to the rest of the drive train. Prop shafts run parallel to the car’s axis and are only common in rear or all-wheel-drive cars, where they transmit power from the engine to the wheels in the rear.

Differentials are intricate gear assemblies that allow one side of the differential to rotate at a different rate than the other. They’re critical for turning smoothly and safely because the wheels on the outer side of the car have to travel a lot farther than the inside wheels. Differentials let this happen.

Gearboxes and Clutches

Gearboxes perform the first step of power transmission: converting the high-frequency back-and-forth motion of the engine’s pistons to lower-frequency circular motion for the wheels. Power is the amount of work done over time and it is, mathematically, the product of the torque and rotational frequency of a spinning gear.

Car engines produce a lot of power in terms of cycle frequency but not all that much torque. The gearbox has several differently-sized gears—you’d recognise them as first, second, third, forth and fifth gears in a typical manual transmission car, for example—that convert frequency to torque in different ratios. Low torque gears are best for accelerating from a full stop while high-torque gears are better for maintaining a speed.

When you shift gears, you need to stop inputting force into the gears for a moment, but you can’t stop the engine. The clutch decouples the gearbox from the engine’s direct output and allows you to change gears safely.

That’s all there is to the basics of transmissions. They’re not all that complicated, but as a potential car owner, you should know how they work. If you’re in the market for car finance, then you might be in the market for car knowledge, so check out the other two articles in our series on car components: engines and exhaust.