Back in the day, when stud-pilot (or “Budd”) wheels ruled the disc wheel world, maintenance professionals dreamed of a system without the inherent limitations of ball seats and inner/outer cap nuts. While they were infinitely better than demountable (or “Dayton”) rims, the wheels still wore out too quickly and the fasteners would “freeze” together or just snap off and break. So when the hub-pilot (or “Uni-mount”) wheel system was introduced, industry professionals welcomed the numerous advantages.
Since the changeover has been complete for well over a decade, the trucking industry has quietly enjoyed the benefits of a superior wheel system. When hub-pilot wheels are properly serviced and maintained, the integrity of the wheel is seemingly limitless because there are no bolt holes to be ground away with each installation. In some applications, aluminum hub-pilot wheels can outlive the vehicle while the lifespan of steel wheels can be extended for years with proper refinishing and maintenance. For the majority of fleets, the hub-pilot wheel is more or less the perfect solution for large trucks and trailers.
Like every component on a vehicle, the application determines the degree of maintenance, which ultimately dictates performance. For example, on the road, a typical tractor spends the majority of its time running at highway speeds, so heat and lateral forces are rarely a factor. On the other hand, refuse and recycling trucks are constantly stopping and starting (which increases brake heat) while twisting and turning (lateral forces). As it turns out, despite good maintenance practices, some vocational operators, such as construction and waste fleets, are struggling to find a way to make hub-pilot wheels work in their applications.
It's possible that a solution was unveiled at the recent TMC Annual Meeting in Tampa, FL. It starts with a set of positioning pins from Alcoa that allow the technician to secure the drum to the hub before installing the wheels. Outboard drums are centered on the hub in the same manner as hub-pilot wheels. If the drum slips off the pilot pad, it creates a gap that technicians cannot see when the wheels are installed. The wheels will appear to be secured to the vehicle, but the unseated brake drum will eventually seat — but improperly — during operation and when it does, the beginnings of a wheel-off are in place. Since the pins are slightly smaller than the bolt holes, they pass through the wheel and allow the technician to install and torque the remaining fasteners. This ensures the outboard drum is properly seated.
The other half of the solution is a new fastener from ITW CIP called the Pacnut. It loosely resembles the standard hub-pilot flange nut, but the design incorporates a stack of threaded Belleville washers. The washers act like cone-disc springs after torque is applied so the fastener's clamping ability is improved. Testing has shown that by using the positioning pins with the Pacnut, fleets in severe-service applications can improve the performance of hub-pilot wheels while reducing the frequency of loose wheels. Of course, everything still depends on the correct installation, including the recommended torque for the fasteners, but it definitely looks like the industry has found a way to make hub-pilot wheels work for almost any fleet.
That being said, I still do not believe that fleets should just abandon the traditional service procedures and components for hub-pilot wheel systems. Millions of these assemblies safely operate on the road every day so there is no indication that wholesale changes are necessary. If a particular operation is experiencing issues with hub-pilot wheel performance and retention, however, the combination of the positioning pins and the Pacnut may be the answer.
