What Cars Have All Wheel Drive

Alright, let's dive into the world of All-Wheel Drive (AWD) systems. You're probably here because you're curious about the differences between various AWD setups, maybe you're planning a modification, or perhaps you're troubleshooting a driveline issue. Understanding AWD is crucial for proper maintenance, performance upgrades, and even just diagnosing strange noises or handling problems. This article will give you a solid foundation, so you can confidently tackle anything from fluid changes to more advanced repairs.

Why This Matters: Understanding Your AWD System

Knowledge of your vehicle’s AWD system isn't just for mechanics. It's essential for informed decision-making when it comes to maintenance, modifications, and even choosing the right tires. Imagine you're experiencing wheel slippage on icy roads. Knowing the type of AWD system in your car—whether it's a part-time, full-time, or on-demand system—will guide your troubleshooting efforts. For example, if you have a part-time system and you're driving on dry pavement with it engaged, you could be damaging your transfer case. Similarly, if you're modifying your suspension, understanding how that affects the AWD system's geometry is crucial to avoid creating new problems.

Key Specs and Main Parts: A Breakdown

Let's look at the core components of an AWD system, keeping in mind that specific layouts vary between manufacturers and models.

The Basics

Engine: The source of power, same as any other car.
Transmission: Gears that multiply torque from the engine. In AWD vehicles, the transmission output is often connected to a transfer case.
Transfer Case: This is the heart of the AWD system. It splits power between the front and rear axles. It can be a simple gear-driven unit or a more complex electronically controlled system. Some transfer cases also include a low-range gear for off-roading.
Front and Rear Differentials: These allow the wheels on each axle to rotate at different speeds, which is necessary for turning. Open differentials send power to the wheel with the least traction, which can be a problem in slippery conditions.
Axle Shafts: These connect the differentials to the wheels, transmitting the power.
Viscous Couplings/Electronic Clutches: Used in some AWD systems to distribute torque between the front and rear axles. These can react to wheel slip by transferring more power to the axle with better traction.
Driveshaft: Connects the transfer case to the front and rear differentials (if needed).

Key Specifications

Key specifications to consider include the torque split (e.g., 50/50, 60/40), the type of differential (open, limited-slip, locking), and whether the system is full-time, part-time, or on-demand. For instance, a Subaru WRX STI might have a full-time AWD system with a 41/59 torque split (front/rear) and a driver-controlled center differential, while a Honda CR-V might have an on-demand system that primarily operates in front-wheel drive until slip is detected.

Symbols: Deciphering the Diagrams

AWD system diagrams often use standardized symbols. Here's a quick rundown:

Solid Lines: Represent mechanical connections like shafts, axles, and linkages.
Dashed Lines: Indicate hydraulic or pneumatic lines for actuation of clutches or other components.
Electrical Lines: Typically represented by thinner lines with arrowheads showing the direction of current flow. These lines connect sensors, actuators, and the ECU.
Circles: Can represent gears, bearings, or hubs.
Boxes: Usually represent control modules (ECU, TCU) or valves.
Colors: Manufacturers often use color coding to distinguish between different types of fluids (e.g., red for transmission fluid, blue for hydraulic fluid).
Icons: Specific icons may represent sensors (wheel speed sensors, yaw sensors), actuators (solenoids, motors), and mechanical components (differentials, clutches).

Pay close attention to the legend on any diagram you're using. It will provide specific definitions for the symbols used in that particular schematic.

How It Works: Power Flow and Control

AWD systems essentially divide the engine’s power to all four wheels. However, how they achieve this varies considerably.

Part-Time AWD: This system typically operates in two-wheel drive (2WD) and can be manually engaged into four-wheel drive (4WD). It usually lacks a center differential, meaning it's only suitable for low-traction surfaces like snow or dirt. Driving on dry pavement in 4WD can cause driveline binding and damage. Common on older trucks and SUVs.
Full-Time AWD: This system is always engaged, continuously sending power to all four wheels. It uses a center differential to allow the front and rear axles to rotate at different speeds, making it suitable for all road conditions. Found on many high-performance cars and luxury SUVs.
On-Demand AWD (Reactive AWD): This system primarily operates in 2WD, typically front-wheel drive (FWD), until it detects wheel slip. When slip occurs, an electronic clutch or viscous coupling engages, sending power to the rear wheels. This system is fuel-efficient but may have a slight delay in engaging AWD. Common on crossovers and smaller SUVs.

Electronic control units (ECUs) play a vital role in modern AWD systems. They monitor various sensors (wheel speed, throttle position, steering angle) and adjust the torque distribution to optimize traction and stability. Some systems even incorporate torque vectoring, which selectively applies braking force to individual wheels to enhance cornering performance.

Real-World Use: Basic Troubleshooting

Here are some basic troubleshooting tips for common AWD issues:

Unusual Noises: Grinding, clunking, or whining noises from the driveline can indicate worn bearings, damaged gears, or low fluid levels in the transfer case or differentials.
Vibrations: Vibrations, especially at higher speeds, could be caused by a damaged driveshaft, worn U-joints, or unbalanced tires.
Poor Traction: If your AWD vehicle is struggling to gain traction in slippery conditions, check the tires for wear and ensure the AWD system is properly engaged (if it's a part-time system). Also, inspect the viscous coupling or electronic clutch for signs of failure.
Warning Lights: An illuminated AWD warning light on the dashboard indicates a problem with the system. Use an OBD-II scanner to retrieve diagnostic trouble codes (DTCs) and consult a repair manual for troubleshooting steps.

Simple Checks: Before you get too deep into the repair, check simple things first. > Check fluid levels in transfer case and differentials. > Are there any visible leaks? > Check for unusual tire wear, meaning alignment could be off.

Safety: Proceed with Caution

Working on AWD systems involves several safety considerations:

Driveline Torque: Before disconnecting any driveline components, ensure the vehicle is properly supported on jack stands and the parking brake is engaged. Driveline torque can cause components to suddenly rotate, potentially causing injury.
Fluid Handling: Transmission fluid, gear oil, and hydraulic fluid can be harmful if swallowed or come into contact with skin. Wear gloves and eye protection when handling these fluids.
High-Voltage Components: Hybrid and electric AWD vehicles may have high-voltage components associated with the electric motors and inverters. Always disconnect the high-voltage system before working on these vehicles. Consult the vehicle's service manual for specific procedures.
Lifting: Ensure the vehicle is properly supported and balanced when lifting.

Critical Components: The viscous coupling or electronic clutch are key components in many AWD systems and can be costly to replace. Proper diagnosis is essential to avoid unnecessary expenses. Be very careful when handling any moving parts within the driveline.

Remember to always consult your vehicle's service manual for specific procedures and safety precautions. Working on AWD systems can be complex, so don't hesitate to seek professional assistance if you're not comfortable performing the repairs yourself.

You should now have a good grasp of AWD systems and their components. With this knowledge, you'll be better equipped to maintain, modify, and troubleshoot your AWD vehicle. Remember, safety is paramount, so always exercise caution and consult the appropriate resources before tackling any repairs. Now, get out there and put that knowledge to use!