When coupled with a hub that has the bearing cup seat-to-seat distance closely controlled, and the addition of a precision machined bearing spacer, PreSet or LMS hubs do not require that the bearings be manually adjusted. By design, the components work together to provide the proper wheel bearing end play without requiring that the technician manually adjust the bearings. Each hub assembly is tested at the factory to insure that when the hub is installed onto the spindle and the spindle nut is tightened to the proper torque, the bearing end play will be in the optimum operating range.
Unitized hub assemblies use a special cartridge type tapered roller bearing system. They are assembled, lubricated and sealed at the factory. They are installed on to the spindle as a sealed, pre-lubricated unit. When the spindle nut is torqued to the proper torque range, no further adjustment is required. Several of the unitized hub assemblies have a unique hub cap that aids in the identification of the wheel end.
Regardless of the wheel end type, they all must be inspected on a regularly scheduled basis. TMC RP 631A lists four levels of recommended inspection. Most wheel end manufacturers also list similar inspection requirements.
The most frequent inspection is the driver pre-trip/in-service inspection. It includes a walkaround inspection where the driver should look for signs of leaks at the hub cap or the wheel seal, or lubricant soaked brake linings. The driver also should look for broken, loose or missing components. If the hub cap has a sight glass, the level and condition of the lubricant needs to be verified.
At each scheduled preventive maintenance inspection, all of the things previously listed should be checked. In addition, the wheels of the vehicle should be lifted and supported, and each wheel s rotated and checked for signs of quiet, smooth operation. Each wheel end should also be checked for signs of excessive end play.
Annually, each wheel end should be re-inspected as just outlined. In addition to these inspections, the hub cap or drive axle should be removed and the wheel bearing end play should be checked with a dial indicator.
If anything of concern is found at any level of inspection, wheel ends with manually adjusted or PreSet/LMS bearing systems should be completely disassembled for inspection. All individual components should be cleaned and inspected when the wheel end is disassembled.
Most manufacturers recommend that the wheel end be disassembled and inspected at 5 years/500,000 miles, or in conjunction with the second brake job. All components should be cleaned and inspected and replaced as necessary.
The exception to this is unitized hub assemblies. Unitized hub assemblies are not serviceable in the field, but should be regularly inspected per the manufacturer’s instructions. If anything of concern is found, the hub should be replaced.
Sealing technology has improved with new materials and designs. Differences between seal manufacturers’ materials and designs make it mandatory that the instructions included with the seal be closely followed for proper installation. The seal should be replaced anytime the hub is removed from the spindle.
There are a variety of commercially available tools to aid in removing the seal from the hub. These tools insert between the seal and the bearing, and are used to pry the seal from the seal bore in the hub.
Never drive the bearing from the inside of the hub to push the seal from the seal bore. Damage to the bearing could occur that may be difficult to detect.
Some types of seals may separate when the hub is removed from the spindle. Use caution to prevent damage to the seal journal on the spindle when the inner portion of the seal is removed from the spindle. After the inner portion of the seal is removed, it may be necessary to use emery cloth to remove corrosion or foreign material from the seal journal on the spindle.
If the old seal is to be returned to the manufacturer for warranty consideration, efforts should be made to reduce damage to the seal from removal. Typically, the seal should not be cleaned before it is returned.
Do not use identification tags attached to the seal by a wire for identification purposes. The wire could damage the seal surfaces making it difficult to determine the failure mode. It is better to place the seal in a plastic bag as is after it has been removed from the vehicle. Mark the bag with the proper identification information.
Care and maintenance will enable wheels to last the life of the vehicle
Helpful tips from ConMet's PreSet®Hubs and SKF Sealing Solutions.
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