Trailer Axle Bearings and Electric Brakes

Trailer Axles-
Bearings and Electric Drum Brakes

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It’s easy to take things for granted. The fact your trailer rolls smoothly down the road, and your rig comes to a quick stop when you hit the brakes, comes to mind. Two key components that bring this level of confidence are the wheel bearings and electric drum brakes on your trailer.

Wheel bearings and electric brakes share living quarters, and have to survive a tough environment. Together, they are subject to heat, structural loads, moisture, and sometimes abuse. To live, prosper, and contribute to your good times they need attention once in a while.

It’s hard to visually inspect brakes and bearings, so a bit of exploratory wrenching is required to get a close look. How often should you pull the wheels and drum? That really depends on the starting point. Off the showroom floor we rightly expect the parts to deliver thousands of trouble free miles. But if it has been a few years, or you just bought a used rig, then it’s a good idea to pull things apart before hitting the road and bring everything to factory specifications.

A few of the variables determining inspection and service times for bearings and brakes are the recommended OEM maintenance schedule, how many miles you’ve driven, exposure to moisture (rain, washing, etc.), temperature extremes, and severity of terrain (hills, curves, bumps, etc.). The more distance you travel and the more demanding the working environment the shorter time between inspection intervals.

Some RVs rolling off the assembly line come with externally greaseable hubs. You simply remove the cap from the end if the axles and pump grease into the exposed Zerk fitting. This process does not replace a full axle service, however it does allow you to “top-off” the bearings with fresh grease, especially convenient if your axles were submerged or experience a long session of driving in the rain or snow.

When it’s time, place your trailer on jack stands and physically remove the wheels. This exposes the brake drum, which holds the wheel bearings. Once the brake drums are off you can visually see the axle spindle and all the brake components.

The first inspection point is the brake shoes. If they are less than 1/16-inch thick or if the linings are cracked, gouged, grease or oil soaked – or seem to be coming loose from the metal backing, it`s definitely time to replace the shoes. Then inspect the inside of the hub/drum assembly. The inside of the drum should be free of grooves, ridges, rust, etc.

Next look at the condition of the brake hardware. It should be relatively clean. The moving parts should be in good working condition. One difference between drum brakes on a trailer compared to a car is that trailer brakes are operated by electricity, not hydraulic pressure. The electricity comes from the tow vehicle’s brake controller and energizes an electromagnet which actuates the brake shoes. The magnets and associated hardware can wear, and the moving parts freeze up.

Most manufacturers provide service limit specifications for the shoes, drums, and magnets so you or your technician can actually measure wear and determine the correct maintenance path.
With the brakes out of the way, the axle spindle and wheel bearing are up next on the service agenda. The bearings are housed on either side of the drum. The bearings should well-greased and spin smoothly, with a slight resistance from the grease. It takes an experienced hand to feel if a bearing is worn. If the bearings are visibly dry, rusted, or show signs of being overheated, it’s probably time for new bearings.

While the drum/hub assembly can be serviced, usually by machining the inside of the drum to provide a fresh braking surface, and the bearings pressed out and replaced, replacing the entire hub may be a more practical solution. New hubs may, or may not, come with new bearings. In either case, make sure the new bearings match the spindle.

However, if everything is in order you can simply repack the existing bearings with wheel bearing grease. This is typically done by hand. Removing the old grease is always a good idea. There may be contaminants in the old grease, and new and old grease may not be interchangeable.

After servicing the brakes and bearings, install the hub over the spindle. There are specifications on how to tighten the hub attaching nut, as overtightening or under tightening the bearings can cause premature wear or catastrophic failure. I have seen experienced techs tighten “by feel”, but following the manufacturers specified procedure is always the best route.

Now, mount the wheels. Apply anti-seize or blue threadlocker to the lug studs, and torque to specification. Test drive the vehicle. Make sure everything is working correctly. Record the servicing on your log book, then hit the road!

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Andrew Newton