Pre-Adjusted Wheel Ends
Pre-adjusted wheel end systems (see Figure 2) are supplied in two different ways. The components may be loose, or the bearings and seals may be supplied already pressed into the hub. The adjustment is achieved when the retention nut/hardware is installed.
A pre-adjusted wheel end assembly can be identified by a spacer between the inner and outer bearings. The pre-adjusted wheel end system, like the adjustable system, can be serviced in the field.
During routine service intervals, or when maintenance is required, be sure to thoroughly clean all the components and inspect the seal, bearings, hub and spacer for unusual wear or damage. Replace the seal whenever the hub is removed from the spindle.
Additionally, all the bearings (cone assemblies and cups) and the spacer should be replaced
whenever they exhibit any sign of distress or damage. The same type of lubricant or compatible original equipment manufacturer (OEM)-approved lubricant should be used during routine maintenance.
If you're wondering if there's anything that should not be done, the answer is "yes." Do not use the spacer if converting a pre-adjusted hub to a traditional adjustable wheel end system.
Also, do not use industry-standard components for pre-adjusted systems. If replacement parts are required, use OEM-specified service parts to maximize performance.
Do not reuse components that are damaged or excessively worn, especially the bearings, spacer, seal and spindle nuts.
Always follow the hub supplier's or OEM's service recommendations and procedures.
Unitized Wheel Ends
In unitized wheel end packaged systems, the bearings, seals and lubricant are pre-installed into the hub. The bearings are either integrated into the hub or pressed in as a separate cartridge.
The bearing adjustment is set during the manufacturing process and the nut acts to retain it on the spindle, making it easier to install. However, it is not possible to replace separate components, and the unitized wheel end isn't serviceable in the field. When one component wears out, the entire system needs to be replaced.
Warning: Do not attempt to disassemble and reassemble unitized wheel end hubs and bearing assemblies. Improper reassembly could lead to failure.
3. Always replace damaged bearings immediately.
In order to know it's time to replace bearing, you need to know how to identify that they are damaged. The most common types of damage occurring in wheel end bearings include:
- Dry, caked lube in the hub caps or any other internal cavity.
- Metal particles in the lube, hub caps, hubs or bearings.
- Heat discoloration on the bearings or any other internal component. Do not confuse heat discoloration, which is non-removable stain and metal flow, with lube staining that is easily removed with fine emery cloth.
- Evidence of the cups or cones spinning or turning (grooves on the cone backface, bore or spindle). See Figure 4.
- Visual wear on any other bearing surface.
- Any dents on the cage of the bearing assembly.
- Spalling (flaking away) of bearing material on races or roller bodies.
- Any raised metal or dents on the rollers or races.
- Failure to replace a bearing under the aforementioned circumstances can result in wheel separation creating a risk of serious bodily injury.
- Failure to follow the noted cautions could create a risk of injury.
- Do not use damaged bearings as their use can result in equipment damage.
- If a hammer and bar are used for installation or removal of a part, use a mild steel bar (e.g., 1010 or 1020 grade). Mild steel bars are less likely to cause release of high-speed fragments from the hammer or bar or the part being removed.
4. Replace cups and cones together.
When replacing tapered roller bearings in adjusted and pre-adjusted wheel ends, it's important to replace both the bearing cups and cones at the same time.
It might be tempting to keep the "good" half of the used set and pair it with a new mate, but the problem is that the old "good" component has a distinct pattern worn into its raceway. Mixing it with the new component may set up edge stresses along the races and result in premature bearing failure.
With headquarters in Evansville, Ind., USA, Accuride Corporation is a leading supplier of components to the commercial vehicle industry. The company’s products include commercial vehicle wheels...
This installment of Heavy Duty TechTips, from The Timken Company, discusses the three main types of wheel bearing systems: adjustable, pre-adjusted and unitized.