The bearings in the axle hub of each wheel allow your trailer wheels to move freely with no issues. The bearings occasionally need basic repairs, which usually consists of repacking each hub with lubrication. If bearing issues are caught early, though, you may need to replace the entire hub or axle assembly.

1. Grinding Noises

One of the most obvious signs of failing bearings is noise when you are driving. When pulling the trailer, it's a good idea to periodically turn off the radio and roll down the windows. If you hear grinding, rumbling, squealing, or rattling from the trailer, then the bearings may be going out. You can also stand on the side of the road while an assistant drives by with the trailer if you are concerned that you may not hear any noises while in the vehicle cab.

2. Hub Heat

When the bearings seize due to a lack of lubrication, friction will be an issue when you are hauling the trailer. Friction leads to heat, which is something you can test for if you are concerned about the state of the bearings. Haul the trailer at highway speeds for no more than 10 minutes. Then, stop and place your hand on the hub of each wheel. If the hub is very hot to the touch, it may be time for a bearing repair.

3. Pulling

Just because the bearings are failing in one hub doesn't mean that all wheels are equally affected. It's not uncommon for the issue to only affect or to be worse in one wheel compared to the others. When this happens, it may feel as though the trailer is pulling or swaying to one side behind you. You can often feel the drag on the towing vehicle, and you may also be going through more gas than usual due to the drag.

4. Sparking

That same friction that leads to heat on the hub can also lead to sparking. Sparks occur when metal rubs on metal, which is what can happen inside the hub if there isn't enough lubrication to allow free motion and keep the bearings from seizing. If you notice sparks from your trailer wheels when you glance in the rearview mirror, it's time to get the trailer to a mechanic as soon as possible. 

5. Spin Issues

You can test the hub bearings without ever driving them down the road. Jack up one wheel. Make sure any brakes are disengaged, and then spin the tire. The wheel should move freely on the hub, without any signs of friction or wobbling. Repeat this test for each wheel. If a wheel doesn't spin freely, then the hub needs a bearing repair.

Contact a trailer repair service in your area if you suspect issues with the hub bearings.