The purpose of the wheel hub is to serve as the glue between the tire and the axle. Tires are attached with studs to the hub assembly. The hub assembly then fits on the axle, which connects the tire component to the rest of the car. Because the wheel hub is the bridge between the tire and the entire vehicle, if one of its parts breaks down, it creates a ripple effect. That could include problems such as impaired steering or a broken axle.
What's going on inside of that wheel hub assembly? A hub isn't a standalone piece of hardware. Instead, it needs a handful of other parts to do its job. The trailer wheel hub looks sort of like a metal donut that slides onto the axle. On either side of the hub, you have the inner and outer bearings. (You can learn more about wheel bearings in How Trailer Bearings Work.) In brief, the bearings are cylindrical pieces that are packed with grease that reduce friction during tire spin. A castle nut at the center of the hub assembly holds the hub and the bearings in place on the axle. A sticklike piece of metal called a cotter pin then secures the castle nut.
The bearings in the hub must stay adequately greased to reduce the heat by-product as much as possible. Also, dirt and water that contaminate the hub can impede tire rotation. For that reason, a grease cap, which is sometimes referred to as a dust cap, fits over the outside of the trailer wheel hub to keep the grease in and the impurities out.
So with all of these parts, how do you go about removing or replacing a trailer wheel hub? We'll discuss installation on the next page.