It’s a lose-lose situation for jobber and repair shop alike when a new wheel or axle shaft bearing fails. The lose-lose parts occurs, for example, when a new axle bearing suffers a catastrophic failure. To ensure against still another bearing failure, the rear axle should be completely disassembled and steam-cleaned to remove the metal particles from the failed bearing. In most cases, the shop absorbs the clean-up and labor cost for replacing the failed bearing, which doesn’t make it a happy customer. Fortunately, most warranty problems can be prevented by addressing the root cause of the original bearing failure and following correct installation procedures, including appropriate cleanliness and workmanship.
Wheel Bearing Construction
Wheel bearings and axle bearings are manufactured in sealed hub assemblies, tapered roller, flat roller, “barrel” roller, and ball bearing configurations. Individually replaceable barrel-roller and ball bearings generally haven’t been used as since the 1950s because they lack the load-bearing capacity of tapered-roller wheel bearings. Bearing manufacturers generally use a tough, but relatively soft base metal to form the body of the wheel bearing. A chemical process is then used to case-harden the bearing’s load-bearing surface for maximum service life.
Failure Patterns
Wheel bearings live in a very tough operating environment because they must support the vehicle weight, endure millions of wheel rotations and survive in extreme heat and moisture without failing. The sealed ball-bearing hub assembly is currently the most popular because it operates at zero bearing end-play to provide the precise operating tolerances required for anti-locking disc brakes. When the sealed bearing hub begins to develop excessive end-play, the first symptom might be an illuminated anti-locking brake system (ABS) warning light because the ABS wheel speed sensor is no longer operating at its specified air gap. To avoid damaging the new bearing hub assembly, the bearing retainer bolts and spindle nut should be lubricated and hand-torqued to specification.
While tapered roller wheel bearings have been with us since the earliest days of the automobile, their need for constant adjustment and maintenance has made them less suitable for use with modern braking and vehicle stability systems. Nevertheless, tapered roller wheel bearings are still used in many heavy trucks, tractors and trailers because of their ability to carry heavy vertical and side-thrust loads.
Unlike sealed bearing hubs, tapered roller wheel bearings require occasional cleaning, inspection, lubrication, and adjustment. So it shouldn’t be a surprise that most tapered roller bearings fail due to incorrect adjustments and incorrect lubricants. When servicing tapered roller bearings, it’s imperative to use a wheel bearing grease that meets manufacturer’s specifications for temperature and water resistance as well as load-carrying ability.
Always recommend selling a new bearing race with each new bearing. Mixing old and new will virtually guarantee failure. And don’t forget to recommend new oil seals when required.
