Most 4WD vehicles have locking hubs on the front wheels. When the 4WD is not engaged, the locking hubs disconnect the axle. They spin freely, and the rear wheels of the car do all the work of moving the vehicle. When 4WD is engaged, the locking hubs lock in the front wheels to the front axle allowing them to get torque from the engine Mud, rust or worn parts inside the hub can prevent the mechanism from sliding in and locking the hub. Anything that binds the internal mechanism can prevent it from sliding and releasing. The most noticeable symptoms may be an increase in fuel consumption, noise on the highway and/or increased front-tire wear. A new locking hub helps improve fuel economy in 2WD when unlocked, reduce the wear of the front axle and lighter steering. Quality: Meet or exceed OEM standard. Fits both RH (passenger side) and LH (driver side) front. Brute strength matters, that is why the bodies of our lock out hubs are crafted from reinforce material, feature anticorrosion and high impact resistant. Compatible with: 1999-2004 Ford F250 Super Duty 4WD1999-2004 Ford F350 Super Duty 4WD1999-2004 Ford F450 Super Duty 4×41999-2004 Ford F550 Super Duty 4×42000-2005 Ford Excursion 4WD2001-2002 Ford Expedition 4WD2001-2002 Lincoln Navigator 4WD. *Fits 4WD models with auto locking hubs only. Part Number: 1C3Z-3B396-CB/ 1C3Z3B396CB/ 600-203/ 600203 Warranty: 12 months hassle-free warranty.sWe value your shopping experience and strive to offer a high-quality product and service. And if you have any problem, contacting us and we will serve you within 24 hours.