What Cars Are All Wheel Drive

Alright, let's dive into the world of All-Wheel Drive (AWD) systems. This article is going to break down the different types of AWD, how they work, and what to look for if you're wrenching on one. Knowing your way around an AWD system is crucial, whether you're planning to upgrade your vehicle for better off-road performance, diagnose a nagging drivetrain vibration, or simply want to understand how your car puts power to the ground. We'll cover the key components, discuss troubleshooting tips, and even point out some potential safety hazards. Think of this as your comprehensive guide to understanding the nuts and bolts of AWD.

Why Understanding AWD Matters

Why bother learning about AWD? Well, for a few key reasons. First, diagnosis and repair become much easier when you understand the system's intricacies. Instead of blindly replacing parts, you can pinpoint the source of a problem. Second, modifications and upgrades are far more effective when based on a solid understanding of the underlying mechanics. Want to lift your Subaru? You need to know how that affects the drivetrain. Third, it empowers you as a car owner. You'll be able to have informed conversations with your mechanic and make confident decisions about your vehicle.

Key Specs and Main Parts of AWD Systems

AWD systems aren't one-size-fits-all. They come in various flavors, each with its own strengths and weaknesses. However, they all share some fundamental components:

Engine: The source of the power, duh!
Transmission: This converts the engine's power to a usable form and sends it to the drivetrain.
Transfer Case: This is the heart of an AWD system. It splits the power from the transmission and sends it to both the front and rear axles.
Front Differential: Distributes power between the front wheels.
Rear Differential: Distributes power between the rear wheels.
Driveshafts (Propeller Shafts): Connect the transfer case to the front and rear differentials, transmitting the rotational force.
Axles: Connect the differentials to the wheels.
Wheel Speed Sensors: These provide data to the vehicle's computer about the speed of each wheel, crucial for many modern AWD systems.
Control Unit (ECU/TCU): Manages the AWD system, using sensor data to adjust power distribution.

Now, let's talk about different types of AWD:

Part-Time AWD: This system allows the driver to manually engage or disengage AWD. Typically found in older trucks and SUVs. In 2WD mode, only one axle (usually the rear) is driven. Engaging 4WD locks the front and rear axles together, providing maximum traction in low-grip situations. Important: Do not use part-time AWD on dry pavement! This can cause driveline binding and damage.
Full-Time AWD (or Continuous AWD): This system is always engaged, automatically distributing power to all four wheels. There are different variations, including:
- Viscous Coupling AWD: Uses a viscous fluid-filled coupling to transfer torque to the axle with more traction. Relatively simple and inexpensive.
- Torsen Differential AWD: Uses a torque-sensing differential to distribute power based on available grip. Offers excellent performance.
- Electronically Controlled AWD: Uses sensors and an electronic control unit (ECU) to monitor wheel slip and distribute power accordingly. This is the most common type in modern vehicles. Often utilizes clutches or other electronically controlled devices to vary the front/rear torque split.

Understanding AWD System Diagrams

AWD diagrams are essential for visualizing the flow of power through the system. They typically use a combination of lines, symbols, and colors to represent different components and their connections.

Symbols and Lines:

Solid Lines: Represent mechanical connections, such as driveshafts and axles.
Dashed Lines: Represent electrical connections, such as wiring harnesses.
Boxes: Represent components like the transmission, transfer case, and differentials.
Circles: Often represent sensors, such as wheel speed sensors.
Arrows: Indicate the direction of power flow.
Clutch Symbols: Show where clutches are located within the system. These are often used in electronically controlled AWD systems to engage and disengage the front or rear axles.

Colors: While not standardized, colors are often used to differentiate between different types of fluid lines (e.g., hydraulic lines for clutch actuation) or to highlight specific components.

How AWD Works: A Deeper Dive

Let's break down how a typical electronically controlled AWD system works:

The engine generates power, which is transmitted to the transmission.
The transmission outputs power to the transfer case.
The transfer case splits the power between the front and rear driveshafts.
Wheel speed sensors constantly monitor the speed of each wheel.
If one or more wheels start to slip (i.e., spin faster than the others), the wheel speed sensors send this information to the ECU.
The ECU analyzes the data and determines the appropriate course of action.
The ECU commands the AWD system to adjust the torque split between the front and rear axles. This can be done by engaging or disengaging a clutch pack in the transfer case, or by applying braking force to the slipping wheel using the vehicle's electronic stability control (ESC) system.
By transferring more power to the wheels with better traction, the AWD system helps the vehicle maintain stability and control.

Real-World Use and Troubleshooting

So, what happens when things go wrong? Here are some common issues and troubleshooting tips:

Vibrations: A common symptom of AWD problems. Can be caused by worn U-joints in the driveshafts, a damaged center support bearing (on longer driveshafts), or a misaligned driveshaft. Check for play in the U-joints and inspect the driveshaft for dents or damage.
Noises: Grinding, clicking, or clunking noises can indicate problems with the differentials, axles, or transfer case. Check the fluid levels in these components. Low fluid can lead to premature wear and failure.
AWD Warning Lights: Most vehicles have an AWD warning light that will illuminate if the system detects a problem. Have the vehicle scanned by a qualified technician to retrieve the error codes.
Uneven Tire Wear: Mismatched tire sizes or excessive tire wear can put undue stress on the AWD system, leading to premature failure. Ensure all tires are the same size and have similar tread depth.

Basic Troubleshooting Steps:

Check Fluid Levels: Inspect the fluid levels in the transfer case, front differential, and rear differential. Use the correct type of fluid as specified by the manufacturer.
Inspect Driveshafts: Look for signs of damage, such as dents, cracks, or worn U-joints.
Check for Leaks: Inspect the transfer case and differentials for leaks.
Scan for Codes: Use an OBD-II scanner to check for any stored trouble codes related to the AWD system.

Safety Considerations

Working on AWD systems can be dangerous if proper precautions are not taken. Here are some key safety considerations:

Driveline Binding: Avoid using part-time AWD on dry pavement. This can cause driveline binding, which can damage the transfer case, differentials, and axles.
Rotating Components: Be extremely careful when working near rotating components, such as driveshafts and axles. Ensure the vehicle is properly supported on jack stands and that the parking brake is engaged.
Fluid Spills: Differential fluid and transfer case fluid can be slippery and messy. Clean up any spills immediately to prevent accidents.
High-Pressure Systems: Some AWD systems utilize hydraulic components. Relieve pressure before disconnecting any hydraulic lines.
Electrical Systems: Disconnect the battery before working on the electrical components of the AWD system.

Important Note: The transfer case is a particularly sensitive and expensive component. Always follow the manufacturer's recommendations when servicing it.

By understanding the fundamental principles of AWD systems, you'll be better equipped to diagnose problems, perform repairs, and even upgrade your vehicle for enhanced performance. Remember safety first, and when in doubt, consult a qualified mechanic.

We have a detailed AWD system diagram available for download. This diagram provides a visual representation of the components and their connections, which can be extremely helpful for understanding how the system works and troubleshooting problems. Contact us to access the file.