Before 1998, most vehicles sold in the United States were equipped with a two-piece wheel bearing system which attached each tire / wheel combo to the car. This unit included inside the assembly a hub assembly and wheel bearings which allow the tires and wheels to spin freely on the vehicle. Inside the bearing is a wheel seal designed to keep the bearings properly lubricated and free from bearings debris, dirt, and other materials.
It is recommended that seals and bearings for cars built before 1998 be serviced every 30,000 kilometres. This service usually includes removing the seal and bearing wheel from each axle, cleaning it, grazing it and repairing any damaged seals. However, most car owners in the US who have vehicles constructed in 1997 or earlier have not completed this significant routine maintenance. As a result, there is greater potential for a broken or failing wheel seal. If this part wears out, it will damage the wheel bearings and typically display a few warning signs indicating wearing out or failure of the bearings.