Manual locking hubs are an important part of most four-wheel-drive systems. In simple terms, these rugged little components lock the wheel hub to the axle to provide additional traction when the transfer case is engaged in either four-wheel High or Low. Hubs are usually found on the front axle of the vehicle, but there are some full-floating axle conversion kits for the rear of vehicles using manual locking hubs.
Within the manual locking hub there is an inner ring called the inner hub. This inner hub has splines on its inside and outside. The inside splines of the inner hub engage with the splines on the axle (sometimes called the driveshaft or halfshaft). The outer part of the manual locking hub has a dial with two position settings: lock (4X4) and free (4X2). When the dial is turned to its locked position, a clutch ring (also having inner and outer splines) inside the hub engages the outer splines of the inner hub, while the outside of the clutch ring is engaged to the inside of the hub body or casing. This locks the whole hub assembly to the drivetrain. Now when the transfer case is engaged and sending torque through the driveshaft, differential, and axles, the locked wheels spin with their rotation.
When the dial is turned to its unlocked (free) position, the clutch is pulled outward from the inner hub and is disengaged. The wheel then spins freely around the inner hub and axle. This action is sometimes referred to as "free wheel," and these types of hubs are known as "free-wheeling hubs." When the hubs are in their unlocked position, it is usually the setting for two-wheel drive.
Locking and unlocking the hubs are done for many reasons. Locking is obvious; disengaging the hubs when four-wheel drive is not being used keeps the differential and front driveshaft from spinning unnecessarily. This prevents wear and tear on the components and U-joints, lessens road noise, and slightly increases fuel economy.
Manual locking hubs come in many shapes and sizes, depending on application, and are made from numerous types of material. Hubs are usually durable and dependable components, even from the OEM assembly lines. Toyota and other automotive manufacturers have used AISIN hubs for years, gaining a reputation for durability and dependability. Aftermarket manufacturers such as Mile Marker, Superwinch, Warn, and newcomer RockCrusher have made a name for themselves by designing and building premium-quality hubs. The hubs are designed and built for dependability and reliability under harsh conditions. Most are so well-built that they are able to handle the torture of today's rockcrawling competitions and survive extreme four-wheel adventures. You will also find these hubs on new vehicles as standard factory equipment, with some made to military specs. Besides durability, another reason for switching to aftermarket hubs would be that some vehicles come with non-serviceable hubs, such as the '84-and-newer Cherokees, and the '87-or-newer Wranglers.
Manual locking hubs are also associated with full-floating axles. In the past, full-floating axles were usually only found on heavy-duty, 3/4-ton-or-larger trucks. Today, numerous manufacturers offer full-floating conversion kits for the rear of just about any four-wheel-drive vehicle. Full-floating axles are stronger than most other axle setups. More importantly, the full-floating axle doesn't support the weight of the vehicle or hold the wheels on, alleviating unneeded pressure on the axle. If an axleshaft is broken, the wheel and tire will stay attached to the axlehousing and not just fall off; this way you can drive the vehicle out of the axle-snapping situation you got it into. If you flat-tow your four-wheeler to and from your favorite trails, an additional advantage of a full-floating axle in the rear is the ability to unlock the rear hubs, allowing the vehicle to freewheel with less front and rear resistance. This will save wear and tear on the rear of the vehicle's components and should also increase fuel economy for the towing vehicle.