The fact that a wheel-end failure can result in such catastrophic consequences on the highway makes it one of the most crucial vehicle components. Since poor bearing adjustment is considered the most frequent cause of wheel-end failure, the industry has worked to develop wheel-end technology that circumvents this problem.
Perhaps the most effective solution to date is the unitized wheel end, a pre-assembled, integrated unit that includes the hub, bearings, seals, lubricant, spindle nut and hubcap. A number of manufacturers offer these premium products, including ArvinMeritor, Dana Spicer and Hendrickson. According to ArvinMeritor, the primary advantages of a unitized system are that it eliminates bearing adjustment, seal installation and periodic lubrication. Because they're sealed for life at the manufacturer, grease contamination is not a problem.
The units are virtually maintenance-free, not only saving fleets time and money, but eliminating the vulnerability to contamination that occurs when individual components are replaced. Although periodic inspections are necessary, they don't involve taking the wheel end apart.
Hendrickson recently introduced the HUS (Hendrickson Unitized System), a wheel end option for axles used on their INTRAAX and VANTRAAX trailer suspension systems. According to the company, this unitized wheel end achieves plus or minus 0.001 in. end-play.
In many cases, unitized wheel ends are joint activities between axle, hub and bearing manufacturers. ConMet, for example, has developed some complete pre-packaged sub-assemblies (hub, bearings, seals, grease) in conjunction with bearing companies for specific axle configurations.
ConMet points out that although unitized wheel ends, which have been available since the mid-'90s, are growing in popularity, market acceptance has not been overwhelming. In the meantime, companies continue to develop products that will help minimize wheel-end failure for fleets that aren't ready to spec the completely unitized, premium systems.
ConMet's PreSet wheel ends, which fit on industry-standard axles, are factory-assembled with preadjusted bearings, making installation easier and more error-free than with traditional wheel ends. According to ConMet, this eliminates the risk of seal misalignment and damage during installation that can cause premature wheel-end failure.
The PreSet wheel ends differ from unitized systems in that they are fully serviceable, do not come pregreased and use a spacer for bearing adjustment. The PreSet wheel end fits industry standard axles, while the unitized product requires a special spindle configuration.
Last month, ArvinMeritor introduced the TRIAD wheel end system, which uses a patented installation procedure from the Hub Nut Corp. to achieve proper bearing pre-load. Called C-PAN (Controlled Position Axle Nut System), it provides controlled bearing preload in the 500-lb. range, which is expected to be the target number recommended by TMC in its upcoming revision of RP-640, according to ArvinMeritor.
The TRIAD wheel-end system can be used on RP-618 (end-play) or 640 (preload) systems. ArvinMeritor says the system's salient feature is the bearing adjustment procedure-it's more manageable and less time-consuming, and basically more reliable, than the traditional two-nut end-play procedure.
The advantage of pre-load bearing adjustment is that it eliminates end-play, providing a tighter bearing setting, for longer wheel-end life.
ArvinMeritor's first introduction of TRIAD is for trailer axles, specifically the TN, TQ and TP units. Although the parts are different, the TRIAD looks similar to the traditional two-nut wheel-end system and can be retrofitted.
Stemco works in conjunction with hub manufacturers to provide a long-life premium product, the Advantage system. Webb Wheel Products, for example, offers a five-year, unlimited mileage warranty on its aluminum hub if it's purchased with the Stemco Advantage System (Pro-Torque axle fastener, Discover seal and Sentinel hub cap.) The hub maker completes the wheel end by adding the hub, seal and bearings, and ships it to the OEM as one assembly, where it is installed on the axle in a slight pre-load condition.
FOR MORE INFORMATION, CIRCLE NUMBER ON REPLY CARD:
Consolidated Metco 321
Dana Spicer 322
Hendrickson International Trailer Suspension Systems 324
Webb Wheel Products 328