By William D. Siuru, Jr., PhD, PE
originally printed in PopUp Times Magazine
Repacking wheel bearings on modern trucks, SUVs and RVs might be beyond the capabilities of many do-it-yourselfers mainly because it usually involves disassembly and assembly of sophisticated disc brake systems. In comparison, repacking of wheel bearing on trailers is relatively easy.
Bearings on today’s vehicles don’t usually have to be touched until a brake job is done. This is not the case with trailers. Wheel bearings on trailers with regular sized tires should be repacked every 10,000 mile on trailers used regularly, especially if they are heavily loaded. You can get by with repacking every two years on trailers that are lightly loaded and do not see many road miles. On trailers with tiny wheels like boat trailers they should repacked as often as every 2,000 miles. The smaller the wheel, the faster the bearing spins and the greater the need for good lubrication.
You should check bearings every time you refuel. They should be warm, but not excessively hot when touched by hand. If you cannot leave your hand on the bearing because it is too hot, better get it checked out.
If you decide to repack trailer bearings, try to get a service manual showing how to do the job. If one is not available, at least find out the proper torquing amount and procedure when you reassemble the wheel. This is critical because a wheel that is too tight or too loose can cause overheating, excessive wear, wheel wobble, or even the wheel falling off. Without an instruction manual, you might make a drawing of how the bearings, seals, washers, nuts are installed so you can put everything back together again correctly. Usually the wheel comes off the hub without the need for a hub puller.
After disassembly, clean all the old grease from the hub, spindle and bearings. Use a brush and parts-cleaning solvent, mineral spirits, or kerosene. Unless you already suspect a bad bearing, you can leave outer cups in the hub. Then carefully inspect the running surfaces of the races, that is the cups, cones and cage. Use a magnifying glass to look for tiny pits, cracks or roughness. While a bit of grease staining is okay, if the parts are straw brown or bluish, the bearing has been overheated by and probably lost it hardness. If there is any doubt about the condition of the bearings, replace with new ones. Use a brass drift or a piece of hard wood and a hammer to gently remove the outer cup from the hub.
If one bearing is bad, it is a good idea to replace both bearings on the same axle since both probably were subjected to the same thing that caused the damage such as overheating or a gritty foreign material. When replacing bearings make sure the part numbers match or are the right interchange parts. Whether you use old or new bearings, every time you remove a wheel bearing, use new oil seals and a new cotter pin in the retaining nut. New grease seals are important so grease does not leak out and ruin the brake shoes.
While you have the wheel apart inspect the condition of the brakes. If worn to their limits or damaged by grease, replace. Also look at the threads on the spindle. If damaged, clean them up with a thread-restoring file or knife-edge file.
Absolute cleanliness is critical when working with bearings since a bit of gritty dirt in the grease can ruin a bearing’s finely machined surfaces in short order. Pack the bearing cage with high-temperature wheel bearing grease, which is different than the grease use to lube chassis components. Work the grease into the being cage by hand. You can eliminate mess and keep grit out of the bearing by putting the bearing and a ball of grease into a plastic bag. Then work the cage with your fingers from the outside. Or use a pair of plastic gloves if you don’t want to get your hands dirty.
If you have a bearing design that doesn’t separate, you might use a bearing packer to insure enough grease gets into the bearing. Also place a thin layer of grease side the hub and on the spindle making sure no grease gets on the brake drum or shoes.
If removed, install inner bearing assembly into the hub. Then insert grease seal in its seat, looking at your drawing to make sure it goes in the right way. Start seal in the bore with thumb pressure and tap the rest of the way in with a light hammer and a hard piece of wood to spread the impact load and avoid deforming the seal. If this turns out difficult, take the unit to a machine shop that has equipment to press in bearings. Lubricate the lip of the seal with a light coating of grease. Reassemble the hub on the spindle and tighten the nut using the proper procedure and the right amount of torque.
If the trailer has a Bearing Buddy and E-Z Lube grease cap, bearing problems are less likely to leave you stranded. The Bearing Buddy typically covers the end of the spindle and there is a grease gun fitting in the center. Because fresh grease only gets to the outer bearing, wheels still should be pulled and repacked normally to grease all bearings. In contrast, the E-Z Lube hub also has a grease fitting which now includes an orifice that routes grease to both the inner and outer bearings. Repacking still needs to be done, but at about half the normal frequency. With both, you can get enough grease into a hot bearing to get you home or a service facility, so carrying a grease gun in you tool box might be a good idea. It could prevent ruining a wheel spindle.
About the Author: William D. Siuru, Jr., PhD, PE, is an Automotive Journalist who lives in San Diego, California. He is a frequent contributor to Pop Up Times. He can be emailed at [email protected]