Truck hub units have the potential to keep trucks on the road longer, with less downtime. Fleet operator Hare Express decided to try them out.

With the development of an integrated hub bearing arrangement that can be used on trucks and trailers, engineers have borrowed a feature from passenger car technology. A hub unit combines bearings and hub in a factory-manufactured assembly that is lubricated, sealed and adjusted for life. Many passenger cars use such an arrangement. Passenger car wheel bearings are critical automotive axle components that experience a wide range of loads and operating conditions. Heavy-duty trucks (over-the-road tractor-trailers), however, experience even more severe usage in terms of considerably higher vehicle road time, consistent long-distance use, inordinately high bearing loads and frequent maintenance.
    Maintenance of the conventional bearing arrangement, with separate bearings, seals and hubs, has long been a serious concern for both owner-operators and truck fleet managers. At Hare Express, a fleet operation near Detroit, Michigan, in the United States, trucks normally accumulate 250,000 miles per year. Company trucks with conventional bearing arrangements are brought in every 100,000 miles as a matter of routine bearing maintenance, says Matt Hare, chief operating officer of Hare Express. However, Hare Express has recently added 20 tractors equipped with Meritor Easy-Steer Plus Axles with SKF Truck Hub Units. Says Hare, “So far, we’ve exceeded 300,000 miles on these units – with no bearing-related problems and zero maintenance. We fully expect the truck hub units to last trouble-free through the warranty period.”

Truck wheel end maintenance
The warranty period covering these particular steer axles with the hub units is 750,000 miles or five years. However, the realistic design life – and the proven test life of the SKF hub units is a great deal longer.
    A considerable number of European units have been in use for 10 years and continue in trouble-free service even today.
    The conventional arrangement of separate, non-integrated bearings, seals and lubricant are maintenance-intensive by nature, making maintenance downtime a fact of life for truck owners. Conventional truck hub bearings require periodic inspections and end play adjustments. Seals often fail well before their projected lifespans. Bearing experts believe that more than 95 percent of all wheel-end bearing failures have occurred because they have failed prematurely due to contamination or poor adjustment rather than because they have reached the end of their fatigue life.
    Seal failure and subsequent oil or grease leakage starves wheel bearings of lubricant, causing excessive operating temperatures and premature bearing failure. Seal failure alone often necessitates expensive bearing and brake lining replacement. When the hub lubricant escapes past the seal, the brake lines are often contaminated. Most hub seal failures are due to in-the-field maintenance problems including improper seal installation, inaccurate bearing adjustments and contaminated lubricant. Frequent bearing and seal maintenance – and downtime – is required to forestall failure of conventional wheel-end components.
    Trailer axle maintenance occurs less often and is more difficult to monitor, in terms of accurate, accumulated road time, than other wheel-end positions. Trailer bearings meet the worst conditions possible for oxidation, condensation and other damaging conditions, having to endure periods of prolonged downtime in freight and other yards.

The truck hub unit solution
The primary objective of truck owners and fleet managers is to eliminate downtime and its considerable costs. A truck or trailer that’s down for any service task – including regular wheel-end maintenance – makes no money for its owners. Truck hub units address this critical issue head on, eliminating wheel-end maintenance and reducing downtime. Both experts and truck owners agree that evolutionary designs, those involving slight modifications to present wheel-end designs, are not acceptable over the long haul. To really prevent wheel seal leaks revolutionary designs are needed.
    Instead of using separately installed, replaced and adjusted items for the wheel end, the truck hub unit is fully integrated – factory assembled and adjusted for life – virtually eliminating the need for maintenance of any kind. In the unlikely event that a unit is damaged in service i.e., by accident, the entire unit can be replaced as a single assembly in less than 30 minutes, with no in-the-field adjustment or lubrication required.
    “Our trucks use external hubs, so we don’t even remove the truck hub units during brake lining replacements,” says Hare. “People are generally skeptical of the term ‘zero maintenance,’ but truck hub units have proven themselves even to our own skeptics.”

Stephen J. Davis  
a business writer based in Philadelphia, Pa.  
photo Dave Gusho