Torque is rotational force or the ability to overcome resistance to rotation. It is the cross product of force and radius. Torque is the amount of force applied tangentially to a circle.
Ask any mechanic who works around a wheel hub, and he will likely tell you that "Happiness is a well-adjusted wheel bearing." In recent years, we have all seen a change in bearing technology, which has changed certain aspects of how you service and maintain your coach wheel ends. For your fleet to stay productive, your service team needs to be aware of all of the new bearing designs; their features and benefits; and required service procedures.
This month's Maintenance Matters will look at the three bearing and two locking-system designs currently in use in MCI coaches, along with the inspection, adjustment, and service procedures for each.
Once the bearings and hub assembly are installed and adjusted, a locking nut system is used to ensure that the adjustment does not change during operation. MCI currently uses both the conventional double-nut locking system and the Pro-Torq™ nut system. Both are very secure locking systems but employ different locking methods. The two locking systems are different and are not interchangeable.
The conventional double-nut system uses two spindle nuts separated by one or more locking washers. One of these washers generally has a bendable tab that is used to secure the outer nut from loosening, while an optional second washer may have a series of alignment holes that index onto a pin on the inner nut. When the outer nut is tightened, it acts as a jam nut holding the inner nut in position.
MCI currently uses three wheel bearing configurations in our modern wheel-end assemblies, as supplied by the axle manufacturer:
During hub installation and bearing adjustment, a small amount of "free play" is normally adjusted into the bearing pack. This allows for expansion of the bearing assembly during operation as it heats up, and the expansion then removes the free play, placing a minor pre-load on the bearings. For tapered roller type bearings, this is an optimum operating condition. The bearings may be either oil or grease lubricated.
At routine intervals as normally prescribed by the axle manufacturer, inspect the bearing assembly for operating condition. This generally involves the service technician rotating the hub assembly while checking for smooth and quiet rotation of the hub, and measuring the free play or end play of the bearing and hub. If the bearing end play measures beyond the prescribed limits, it should be adjusted. Any roughness or noise in the bearings will require that the bearing and hub components be serviced as needed.
With the coach securely supported and wheel(s) removed:
Ensure that the oil-filled hub is filled with the proper lubricant.
At routine intervals as normally prescribed by the axle manufacturer, disassemble, clean, inspect, and then reassemble and adjust the entire bearing package. Any worn or damaged parts should be replaced with new ones during reassembly.
The Pre-Set bearing design is a low-maintenance assembly. Like conventional bearings, Pre-Set bearings use the tapered roller design. Unlike the conventional bearing, it also uses a precision spacer between the inner and outer bearings, and it is used in conjunction with a precision-machined hub assembly. When installed, the spacer correctly positions the bearings' seating depth into the bearing cups, automatically setting the correct bearing preload onto the assembly. No adjustment is necessary.
As mentioned earlier; the Pre-Set bearing requires no adjustment since the bearing preload is set by the spacer.
At routine intervals as normally prescribed by the axle manufacturer, disassemble, clean, inspect, and then reassemble and adjust the entire bearing package. Any worn or damaged parts should be replaced with new ones during reassembly. Note that the spacer may be replaced alone if needed. Replacing the bearings requires replacement of all components, bearings, cups and spacer.
The Unitized Wheel End (UWE) is a maintenance-free complete hub assembly that uses a pre-lubricated and sealed bearing assembly. The hub assembly is composed of a wheel-end adaptor, rotor and unitized hub bearing mounted to the spindle. The bearing assembly requires no maintenance and is not adjustable. Periodic inspection is required to maintain performance.
As with all other bearing assemblies, rotate the hub assembly while checking for noise or rough operation. Check end play of the bearing assembly as described above. Any roughness, noise, or end play will require that the bearing assembly be serviced.
(always consult the appropriate maintenance manual for your coach for exact specifications and procedures)
The UWE wheel end is a nonadjustable bearing assembly. Any end play of the bearing requires that the bearing be serviced.
Once the assembled UWE bearing is mounted to the spindle, the spindle nut is torqued to 600 foot pounds.
The UWE wheel bearing assembly is a non-serviceable unit. Any roughness, noise or end play requires that the bearing assembly be replaced.
Always consult your MCI Maintenance Manual or Arvin-Meritor manual MM-0409 for specific information, procedures and specifications. The Arvin-Meritor manual is available by calling MCI Customer Service at 800-323-1290.
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