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How Trailer Wheel Hubs Work

Installing Trailer Wheel Hubs
Replacing trailer wheel hubs is usually a task you can perform on your own, without having to pay a mechanic.
Replacing trailer wheel hubs is usually a task you can perform on your own, without having to pay a mechanic.
Rusty Jarrett/Getty Images

Re­moving or replacing trailer wheel hubs is something that you can do without having to pay the mechanic. It shouldn't take much manpower to assemble or disassemble, although, you'll want to keep track of all the parts you're handling. A standard toolbox with a hammer, pliers and wrench should sufficiently arm you for the task. You'll also want bearing grease on hand and, if you're performing regular maintenance on a hub assembly, a solvent to dissolve old grease on the bearings.

When you're purchasing a trailer hub assembly, there's some valuable information to know in order to make the correct selection. Wheel hubs aren't one-size-fits-all parts. They vary in dimensions based on the si­ze of the trailer wheels and the bearing load. Before you buy, you should:

  • Find out how many stud holes should be in the hub. Hub assemblies usually come with either four or five holes around the circumference. Those slots are for studs that join the tire hub cap to the wheel hub.
  • Measure the diameter of bolt hole in the center of the hub. That is where you screw in the castle nut to hold everything in place. Most wheel hubs have bolt hole diameters between 4 and 6 inches (10 and 15 centimeters), divided into half-inch increments. To obtain that figure, measure from the center of that large bolt hole to the center of a stud hole, and divide that number by two [source: Eastern Marine].
  • Know the inner and outer bearing size. You won't have to pull out your ruler for this one since most bearing have a reference number engraved on them that signify their diameter. The dealer you buy the hub from should have that chart available, or you can find it online.

Once you have your wheel hub assembly with the correct specifications, it's time to install. There are a couple of tips for hub installation to prevent later problems with your tires. First, spread a thin coating of the bearing grease on the inside of the hub before you slide it onto the axle. You don't want a lot on there -- just enough to help it slip on easily. Also, when you tighten the assembly in place, don't overdo it. If you adjust your castle nut correctly, the hub shouldn't move more than a .25 inches (.6 centimeters) after the tire is attached [source: e-trailer].

Up next, we'll learn about trailer wheel hub kits that contain entire hub assemblies. If you're installing a new hub, these kits can simplify the process.