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Understanding 4WD and AWD Systems



Do you get confused by the different drive systems that car makers use to provide power to all four wheels? Don’t feel bad, you aren’t alone. There are many different systems out there and the terminology they use doesn’t help the situation. In this article, we will explore the basics of the main two systems: Four Wheel Drive and All Wheel Drive.

Terminology

As we mentioned, the terminology used by the different carmakers can sometimes be a little confusing, so before we get started explaining how they work, let’s look at what the general terms we will be dealing with:

Four Wheel Drive (4WD) – This is the original term for drive systems that power all four wheels. Usually, when a manufacturer says that a car has four-wheel drive they are referring to a part-time 4WD system. This means that all four wheels are switched on only when extra traction is needed, such as off-road or in slippery conditions. The rest of the time, the vehicle is driven in 2 wheel mode.

All Wheel Drive (AWD) – These are newer systems that are designed to provide power to all four wheels, when needed. In other words, there is no switch to engage any of the wheels. Usually abbreviated as AWD, All Wheel Drive systems are very popular today and many of the car makers offer them.

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Components of a 4WD System

The main components of any 4WD system are the two differentials (one for the front axles and one for the rear axles) and the transfer case. The transfer case is the device that connects the engine to the two differentials. In addition, 4WDs may have locking hubs, and advanced electronics controlling all the components to aid in the shifting process.

The operation of a 4WD system is rather simple: the vehicle is powered by the rear two wheels and when 4WD is needed, the driver switches on the front two wheels. Sometimes the process of switching is done by a shifting lever on the floor and other times via push-button controls on the dash.

Components of an AWD System

The main parts of an AWD system are similar to a 4WD system. There are two differentials and a center-mounted transfer case. The big difference between the two is that there is no switch to engage the second set of wheels. AWD systems are controlled by sophisticated computer that does the thinking for you. It works by constantly monitoring each wheel and when slippage is detected it applies power to the wheels that need it.  Technically all four wheels aren’t powered all the time but the system is still called AWD drive because all four wheels are capable of applying torque when necessary.

Which system is best?

We asked the opinion of Brown’s Automotive Group of Patchogue, a local Jeep, Dodge, Chrysler, Ram dealer in Patchogue, NY, concerning 4WD and AWD systems. They say both systems work well but each has a particular area that it specializes in. Generally speaking, larger trucks and vans use 4WD systems because they can be built beefy. Since full four wheel drive is rarely needed, owners don’t mind shifting it into 4WD when needed. AWD drive systems are better suited for vehicles where no interaction is necessary when driving. This is why you see AWD systems on sedans, minivans and SUVs. They are systems that just do their job without any human interaction.

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