• How a Drivetrain System Works

    Automobiles are complex machines and you may have found yourself wondering at one point or another what exactly a drivetrain is and what the drivetrain parts are. This article will help give you a basic understanding of what the parts of the drivetrain are and how they work.

    Engine and Transmission

    The engine is what provides the power to move your vehicle. The transmission allows your engine to operate within a relatively small range of speeds whether the car is stopped, accelerating or cruising. This is accomplished through a set of gear ratios within the transmission.

    The three types of transmissions commonly used today are manual transmissions, automatic transmissions, and continuously variable transmissions (CVTs). In manual and automatic transmissions, gear ratios are pre-determined and selected by either the driver or automatically by the transmission. In a CVT, the gear ratios continuously change based on the speed of the car.

    Transmissions and differentials can be found in every car, but there are a variety of configurations that effect how the engine’s power will ultimately reach the ground.

    Clutch and Torque Converter

    Between the engine and the transmission is the component that allows the engine to be de-coupled from the transmission, allowing your engine to run while the vehicle is not moving.

    In a manual transmission, this is accomplished by the clutch. When you press the clutch pedal inside the car, the parts inside the clutch completely separate the engine from the transmission, and when you release it, the parts come into contact again.

    In an automatic transmission, this is done by the torque converter. Its inner workings are comprised of two fans set facing each other. When one is turned on, the air it blows hits the other fan’s blades, causing them to turn. A torque converter works in much the same way, only it is self-contained and uses transmission fluid instead of air. At low engine speeds, there is not enough force to turn the blades on the transmission side, allowing the engine to run while your vehicle sits still.

    Front-Wheel and Rear-Wheel Drive

    In a front-wheel drive vehicle, the transmission sits next with the engine in the engine bay. Power flows from the engine to the transmission and then to the differential, which is integral to the transmission in a front wheel drive vehicle.

    In these designs, the differential is usually incorporated into the transmission, making them one unit. A majority of newer cars are front wheel drive, as it is an easy setup for the average driver because the vehicle is less likely to lose control if the throttle is used too aggressively.

    Rear wheel drive cars use a driveshaft (connected to the transmission) to send power to the back wheels. In this type of car, the transmission sits rearward of the engine bay behind the engine, and the differential is a separate unit located between the rear wheels. In this configuration, the front wheels receive no power and are used solely for steering.

    All Wheel and Four Wheel Drive

    In an all-wheel or four wheel drive vehicle, power is sent to all four wheels. The transfer case distributes power to the front and rear differentials, and is either integral to the transmission or a separate unit. All-wheel drive systems allow the front and rear wheels to rotate at different speeds while four wheel drive systems don’t.

    A common all or four-wheel drive setup uses a transmission similar to what is found in a front wheel or rear drive car. One additional component in this system is called a transfer case. In a four-wheel drive truck, the transfer case will essentially force the front wheels to spin along with the rear. This greatly enhances traction on slippery surfaces. It is, however, different from an all-wheel drive configuration.

    An all-wheel drive system will allow all four wheels to spin at different speed. They usually require no driver interaction. Some electronic all-wheel drive systems will only activate when the onboard all-wheel drive computer detects a wheel slipping. In these systems, all the traditional all-wheel drive components are present, but may only work when they are needed. In a full time all-wheel drive system all four wheels receive engine power all the time. Usually, these systems will feature less electronic intervention than their part-time counterparts.


    From the transmission, power moves to a component called the differential. A differential is necessary because, as a vehicle goes around a corner, the wheel closer to the inside of the turn must travel at a different speed than the wheel on the outside. The inside wheel technically has to travel a shorter distance, so the outer must move more quickly to make up the difference.

    The differential allows the driven wheels to spin at different speeds. This allows the vehicle to take turns smoothly. Two differentials are necessary when all four wheels are powered.

    Constant Velocity and Universal Joints

    Constant velocity and universal joints allows power transfer to components that move with the suspension, such as the wheels. CV joints are often used for the axle shafts that transmit power from the differential to the wheels while universal joints are generally used for drive shafts.

    Maintenance schedules for each configuration vary, and the best way to assure a worry free service life is to follow the instructions provided by your vehicle’s manufacturer. Those looking for a new car should keep in mind that each type of drivetrain has a very different purpose and feel. Prospective buyers are advised to try each layout to determine their own personal preference before making their final purchase. Click here for more information on other types of performance parts.