What Is Difference Awd And 4wd

Understanding the difference between All-Wheel Drive (AWD) and Four-Wheel Drive (4WD) is crucial for making informed decisions about vehicle purchases, modifications, and even basic troubleshooting. Knowing the nuances of each system can prevent costly mistakes and ensure you're getting the right capability for your needs. Whether you're planning an off-road adventure, dealing with snowy commutes, or just want to understand your vehicle better, this article will break down the technical details in a clear, approachable way. We have the complete system diagrams available for download – contact us for access.

Purpose: Unlocking Drivetrain Mastery

This information is indispensable for several reasons:

• Repairs and Maintenance: Accurately diagnosing drivetrain issues requires a solid understanding of how AWD and 4WD systems function. Knowing the components and their interactions helps pinpoint the source of problems.
• Modifications: Upgrading or modifying your vehicle's drivetrain demands precise knowledge of its current setup. Incorrect modifications can lead to decreased performance, damage, or even safety hazards.
• Vehicle Selection: Choosing the right vehicle for your needs depends heavily on understanding its drivetrain capabilities. An AWD crossover might be perfect for snowy roads, while a 4WD truck is better suited for serious off-roading.
• General Knowledge: As an experienced DIYer, expanding your knowledge base about automotive systems empowers you to perform more complex tasks and communicate effectively with mechanics.

Key Specs and Main Parts

Both AWD and 4WD systems aim to deliver power to all wheels, but they achieve this in fundamentally different ways. Here's a breakdown of the key specs and components for each:

All-Wheel Drive (AWD)

AWD systems are typically designed for on-road and light off-road use. They are generally always engaged, meaning the system is constantly active.

• Key Specs:
  • Engagement: Typically automatic and full-time.
  • Torque Distribution: Varies depending on the system, but often favors the front wheels (e.g., 60/40 front/rear split). Advanced systems can vary torque distribution dynamically.
  • Differential: Typically uses open differentials or viscous couplings to allow for wheel speed differences. Some systems use electronic limited-slip differentials (eLSD).
  • Transfer Case/Power Transfer Unit (PTU): Splits power between the front and rear axles. The PTU is often smaller and lighter than a traditional transfer case.
• Main Parts:
  • Engine: Provides the power source.
  • Transmission: Transmits power from the engine.
  • Power Transfer Unit (PTU): Splits power between the front and rear axles.
  • Front Differential: Allows the front wheels to rotate at different speeds.
  • Rear Differential: Allows the rear wheels to rotate at different speeds.
  • Driveshaft(s): Connect the PTU to the rear differential.
  • Axle Shafts: Connect the differentials to the wheels.

Four-Wheel Drive (4WD)

4WD systems are designed for more demanding off-road conditions. They are typically part-time systems, meaning they are engaged only when needed.

• Key Specs:
  • Engagement: Typically manual or electronic, requiring the driver to engage the system.
  • Torque Distribution: Typically a fixed 50/50 split between the front and rear axles when engaged.
  • Differential: Often uses locked or limited-slip differentials for maximum traction. Open differentials can be used, but are less effective off-road.
  • Transfer Case: A more robust unit compared to a PTU, allowing for low-range gearing.
  • Low Range (4L): A gear reduction that significantly increases torque, ideal for crawling over obstacles.
• Main Parts:
  • Engine: Provides the power source.
  • Transmission: Transmits power from the engine.
  • Transfer Case: Splits power between the front and rear axles, and provides low-range gearing.
  • Front Differential: Allows the front wheels to rotate at different speeds (may be locked).
  • Rear Differential: Allows the rear wheels to rotate at different speeds (may be locked).
  • Driveshaft(s): Connect the transfer case to the front and rear differentials.
  • Axle Shafts: Connect the differentials to the wheels.
  • Manual or Electronic Shift Mechanism: Used to engage and disengage 4WD.

Symbols and Abbreviations

Understanding the symbols used in drivetrain diagrams is crucial for interpreting schematics and troubleshooting. Here are some common symbols:

• Solid Lines: Represent mechanical connections, such as driveshafts or axles.
• Dashed Lines: Represent control signals, such as electronic signals for engaging a differential lock.
• Gear Symbols: Indicate gears within the transmission, transfer case, or differentials.
• Differentials: Usually represented by a circle with internal gears. Locked differentials may be depicted with a lock symbol.
• Transfer Case/PTU: Depicted as a box with gears and shift mechanisms.
• Abbreviations:
  • PTU: Power Transfer Unit
  • eLSD: Electronic Limited-Slip Differential
  • 4H: Four-Wheel Drive High Range
  • 4L: Four-Wheel Drive Low Range
• Color Coding: Some diagrams use color coding to differentiate between components (e.g., blue for hydraulics, green for electronics).

How It Works

AWD Operation

In an AWD system, the engine's power is delivered to the transmission, which then transmits it to the PTU. The PTU splits the power between the front and rear axles. Differentials at both axles allow the wheels to rotate at different speeds, which is necessary for turning on paved surfaces. If one wheel loses traction, the system will attempt to redistribute power to the wheels with more grip. This can be achieved through electronic systems that brake the spinning wheel, or through mechanical systems like viscous couplings or limited-slip differentials.

4WD Operation

In a 4WD system, the engine's power goes to the transmission, which then connects to the transfer case. The transfer case allows the driver to select between 2WD (rear-wheel drive), 4H (four-wheel drive high range), and 4L (four-wheel drive low range). When 4WD is engaged, the transfer case locks the front and rear driveshafts together, forcing them to rotate at the same speed. This provides maximum traction in slippery conditions but should only be used on surfaces where wheel slippage is possible (e.g., dirt, snow, gravel) to avoid driveline bind-up. Low range gearing significantly increases torque output, allowing the vehicle to crawl over obstacles.

Real-World Use and Basic Troubleshooting

• AWD Troubleshooting:
  • Vibrations: Can indicate a failing PTU, worn driveshaft U-joints, or a damaged differential.
  • Noises: Whining or grinding noises from the PTU or differentials can indicate bearing failure or low fluid levels.
  • Check Engine Light: Can be triggered by issues with the electronic control system for the AWD system.
• 4WD Troubleshooting:
  • Difficulty Engaging/Disengaging: Can be caused by a faulty shift motor, worn shift linkage, or a sticking transfer case.
  • Binding: A common symptom of using 4WD on paved surfaces. Avoid using 4WD on high-traction surfaces.
  • Noises: Clicking or popping noises from the differentials can indicate worn CV joints or damaged gears.

Safety Considerations

Working on drivetrain components can be dangerous. Here are some key safety precautions:

• Secure the Vehicle: Always use jack stands when working under a vehicle. Never rely solely on a jack.
• Disconnect the Battery: Disconnect the negative battery cable before working on any electrical components.
• Wear Safety Glasses: Protect your eyes from flying debris.
• Use Proper Tools: Use the correct tools for the job to avoid damaging components and injuring yourself.
• Driveline Bind-up: Never use 4WD on high-traction surfaces (like dry pavement). This can cause driveline bind-up, which can damage the transfer case, differentials, and axles.
• Rotating Components: Be extremely cautious around rotating components like driveshafts and axles. Keep hands and clothing clear.
• High Pressure Fluids: Be aware that some AWD systems use high-pressure hydraulic fluids. Follow proper procedures for depressurizing the system before disconnecting any lines.

By understanding the differences between AWD and 4WD systems, you'll be better equipped to diagnose problems, perform maintenance, and make informed decisions about your vehicle. Remember to always prioritize safety and use the correct tools and procedures. For detailed diagrams and further assistance, please contact us to access the complete files.