Free wheel hubs, also known as locking hubs or freewheeling hubs, are specialized components primarily found in four-wheel drive vehicles that serve a critical function in the drivetrain system. These mechanical devices allow drivers to engage or disengage the front wheels from the front axle, providing significant benefits in terms of vehicle performance, fuel efficiency, and component longevity. When properly maintained, free wheel hubs enhance both on-road comfort and off-road capability.
What Are Free Wheel Hubs?
Free wheel hubs are components fitted to the front wheels of many four-wheel drive vehicles, particularly older models. They function as a disconnection point between the front axle and the wheels, allowing the wheels to rotate freely when four-wheel drive is not needed. This disconnection means that when operating in two-wheel drive mode, the front drivetrain components (including the axle, differential, and driveshafts) remain motionless rather than spinning unnecessarily.
The hub is the component where the wheel directly mounts to, positioned outside the axle. When engaged or "locked," the hub connects the wheel to the axle, enabling power transmission from the drivetrain to the front wheels. When disengaged or "unlocked," the wheel can rotate independently of the axle, effectively converting the vehicle to two-wheel drive operation.
Working Mechanism
Free wheel hubs utilize a clutch-like mechanism that either connects or disconnects the wheel from the axle. In essence, they function as a one-way clutch that transfers torque in only one direction. When locked, torque from the drivetrain is transferred to the wheels; when unlocked, the wheels rotate independently with no power transfer occurring.
The internal components typically include:
· An inner race connected to the axle
· An outer race connected to the wheel
· A locking mechanism (which varies by design)
· Springs and other engagement components
Types of Free Wheel Hubs
Free wheel hubs come in several variations, with the two main categories being manual and automatic locking hubs.
Manual Locking Hubs
Manual locking hubs require the driver to physically rotate a dial on the hub to engage or disengage four-wheel drive. The driver must exit the vehicle and turn the hub's dial to the "LOCK" position to engage the front wheels with the axle before using four-wheel drive.
The original manual hubs were developed in 1948 by Arthur Warn for surplus WWII Jeeps to improve their performance on pavement. These early hubs allowed the front wheels to be disconnected from the drivetrain, improving fuel economy and reducing wear.
Today's manual hubs, such as those manufactured by WARN, are known for their durability and complete disconnection from the drivetrain. They're often constructed with all-metal components for maximum strength and longevity.
Automatic Locking Hubs
Automatic hubs engage and disengage without driver intervention outside the vehicle. When the transfer case is shifted from 2WD to 4WD, the application of torque to the axle causes a splined collar inside the hub to slide onto the axle's splined stub shaft and lock automatically.
While automatic hubs offer the convenience of "on-the-fly" engagement, they generally don't provide as complete a disconnection as manual hubs. This means some drivetrain components may still rotate even in two-wheel drive mode, potentially reducing the fuel economy benefit.
Mechanism Variations
Several mechanical designs are used in free wheel hubs:
1. Cam Clutches: These use multiple cams arranged between inner and outer races with no backlash. When torque is applied in one direction, the cams lock the races together; in the opposite direction, they allow free rotation.
2. Sprag Clutches: These utilize non-revolving asymmetric figure-eight shaped sprags instead of cylindrical rollers. When rotating in one direction, the sprags tilt slightly and wedge between races due to friction; in the other direction, they slip or freewheel.
3. Ramp & Roller Clutches: These consist of an outer race with a cylindrical inside diameter, an inner race with ramps, and spring-loaded rollers. When rotation occurs in the drive direction, the rollers engage with the ramps to lock the races together.
Benefits of Free Wheel Hubs
Free wheel hubs offer several significant advantages to four-wheel drive vehicle owners:
Improved Fuel Economy
The primary benefit of free wheel hubs is increased fuel efficiency. By disconnecting the front wheels from the drivetrain when four-wheel drive isn't needed, the engine no longer has to turn the front axle, differential, and driveshafts. This reduction in mechanical resistance can improve fuel economy by as much as 1 mile per gallon, depending on the vehicle.
Reduced Wear and Tear
Disconnecting the front drivetrain components when not in use significantly reduces wear on these parts. With the hubs unlocked, the front differential, CV joints, universal joints, and driveshafts remain stationary rather than spinning unnecessarily. This translates to extended component life and potentially lower maintenance costs over the vehicle's lifetime.
Additional Benefits
Other advantages of free wheel hubs include:
· Quieter operation due to fewer moving components when in two-wheel drive mode
· Reduced vibration through the drivetrain and into the cabin
· Enhanced driving comfort on paved roads
· Maintained four-wheel drive capability when needed for off-road conditions
· Reduced tire wear when operating in two-wheel drive mode
Maintenance and Common Issues
Like all mechanical components, free wheel hubs require periodic maintenance and can develop problems over time.
Common Problems
The most frequent issues with free wheel hubs include:
1. Engagement Failures: Hubs may fail to engage properly, preventing the front wheels from receiving power. This is often indicated by grinding noises or slipping when shifting into four-wheel drive.
2. Disengagement Failures: When hubs fail to disengage correctly, front drivetrain components continue to spin unnecessarily, causing increased fuel consumption, more road noise, and accelerated component wear.
3. Binding and Sticking: Corrosion, dirt, or excessive grease can cause the hub mechanism to bind or stick in either the engaged or disengaged position.
Maintenance Tips
To keep free wheel hubs functioning properly:
1. Regular Cleaning: Excessive dirt, mud, or grease can prevent proper operation. Clean the hubs periodically, especially after off-road use.
2. Proper Lubrication: While over-greasing can cause problems, appropriate lubrication is essential. For some hubs, automatic transmission fluid (ATF) is recommended rather than grease.
3. Periodic Engagement: Even if primarily driving in two-wheel drive mode, manufacturers often recommend engaging the hubs (even in 2WD) for several miles each month to lubricate the front drivetrain components.
4. Inspection: Regularly check for signs of wear or damage, particularly if you notice unusual noises or difficulty engaging four-wheel drive.
When maintenance isn't sufficient and hubs fail, aftermarket replacements are available. Some owners choose to convert from automatic to manual hubs for increased reliability, especially in off-road applications.
Conclusion
Free wheel hubs represent an essential component in many four-wheel drive vehicles, offering a clever solution to the inherent inefficiency of permanently engaged four-wheel drive systems. By allowing drivers to disconnect the front wheels from the drivetrain when four-wheel drive isn't needed, these components provide significant benefits in terms of fuel economy, component longevity, and driving comfort.
While newer four-wheel drive vehicles may incorporate different technologies to achieve similar results, traditional free wheel hubs remain relevant for many older vehicles and continue to be manufactured as aftermarket upgrades. Understanding how these components work and maintaining them properly ensures optimal performance both on and off the road, maximizing the versatility that makes four-wheel drive vehicles so popular.
Whether manual or automatic, properly functioning free wheel hubs deliver the best of both worlds: the efficiency and comfort of two-wheel drive for normal road use, with the capability of four-wheel drive available whenever challenging conditions demand it.
