Inspecting used truck parts before placing them back into service is always a good practice. Even the most diligent technicians can be misled, however, if component performance has been compromised by problems that are not mentioned in normal inspection guidelines, not visually apparent, or are so rare that it's something a technician has never encountered.
Axle end components, especially tires and wheels, are good candidates for routine inspections since tires are considered normal “wear” items and used casings are valued assets if removed for retreading prior to excessive wear or late tread-life damage. It's also important because problems can affect vehicle handling and safety.
Tire and wheel makers provide information designed to help fleets through the inspection process, including specific measurements or visual distinctions to decide whether or not the part can be returned to service. In addition, analysis guidelines and out-of-service criteria are available from The Technology Maintenance Council, Item # T0121.
But what happens when the condition has no visible symptoms and there are no readily available in-field test tools to identify the problem?
A few wheel-end conditions come to mind. For example, tire/wheel assemblies that have been subjected to extreme heat, such as that caused by brake failure or vehicle or tire fires, are often unusable. While charring, cracking or brittle areas will typically show up on the tires, the wheels may look just fine after a routine cleanup.
What may not be obvious is that the heat has changed the metallurgy of the wheel, resulting in lost strength, compromised durability and distorted dimensions. Remember that the tires and wheels support the entire weight of the vehicle using high inflation pressures in a contained air cavity. They also transmit the forces needed for acceleration, braking and steering.
Wheels that have been subjected to extremely high voltages or otherwise functioned as an electrical conductor can also become damaged beyond usable limits. Unfortunately, this type of abuse is rarely quantified and often leaves no visible symptoms. Insurance adjusters often complicate matters by insisting that the wheels “look” to be in normal condition.
What can a diligent maintenance person do to avoid such problems? First, any vehicle that has been involved in a high-damage accident, been even partially burned, contacted high voltage lines, or encountered other questionable circumstances, should be quarantined to prohibit parts scavenging.
Second, if exposure to high heat is suspected, a quick wheel check involves rolling it across a flat floor surface to see whether or not it rolls in a straight line. If the wheel turns (usually to the open side), remove it from service. If it appears to roll true, continue with the rest of your inspection procedure. Precision tapes are available to measure bead seat diameters. Contact your tire or wheel supplier or The Tire and Rim Assn. for details (e-mail: [email protected]).
If you have any doubt about a component's safety, ask the manufacturer to provide recommendations for inspection procedures and physical inspection assistance. Alcoa Wheel Products (800-242-9898); Accuride (800-869-2275); and Hayes Lemmerz International are sources for technical advice and assistance. It's usually best to contact the company that made the component you're concerned about.
Keep in mind that in cases of high heat exposure, there may be more than meets the eye.