Wheel bearing service, often called “packing a bearing,” involves thoroughly cleaning and refreshing the lubricant inside a wheel’s tapered roller bearings. This maintenance ensures the bearings are fully saturated with fresh grease, preventing metal-on-metal contact between the rollers and races. Proper lubrication minimizes friction and dissipates heat, preventing premature component failure and potential wheel separation. Since the lubricant breaks down and becomes contaminated over time, routine repacking extends the operational life of the wheel end assembly.
Preparation and Component Inspection
Before applying new lubricant, disassemble the wheel end and thoroughly clean the old grease from all components. Wear appropriate safety gear, including gloves and safety glasses, while using a dedicated cleaning solvent or parts cleaner. The goal is to remove every trace of contaminated grease from the bearing rollers, the cage, and the inner and outer races. This ensures a pristine surface for the new lubricant to adhere to.
After cleaning, meticulously inspect the components to determine if the bearing assembly can be reused. Examine the bearing rollers and races for signs of damage, such as pitting (small indentations) or spalling (flaking of the hardened metal surface). Look for heat discoloration, which manifests as a blue or brown tint on the steel, indicating excessive temperatures. Any sign of scoring, flat spots on the rollers, or metal flakes embedded in the old grease indicates a compromised bearing that must be replaced.
The lubricant of choice is typically an NLGI No. 2 Lithium Complex grease. This grease is engineered to perform reliably under the high temperatures generated by braking systems. It provides superior protection against wear, corrosion, and water washout. Using the correct type of grease is essential, as mixing different formulations can compromise performance and lead to premature breakdown.
Applying New Lubricant
The technique for applying new lubricant is critical, as the grease must be forced deep into the bearing’s internal structure to fully coat the rollers and races. The objective is to achieve 100% saturation of the bearing cavity, replacing all air and old residue with fresh grease. This is accomplished by forcing the grease between the cage and the tapered rollers until it is extruded from the opposite, smaller end of the assembly.
One common and effective approach is the manual packing method, often called the palm method. Place a generous dollop of grease in the palm of one hand, then press the larger diameter edge of the bearing firmly into the grease. This pressure forces the lubricant through the gaps between the rollers and the cage. Rotate the bearing in small increments, continuously forcing the grease into the assembly until a visible ring of new lubricant is extruded uniformly from the smaller side of the bearing cone.
Alternatively, a dedicated bearing packer tool offers a faster and less messy way to pack the bearing. The tool works by placing the bearing into a central reservoir and using a plunger or grease gun to apply hydraulic pressure to the lubricant. This pressure uniformly pushes the new grease through the internal passages until it appears on the opposite side. Regardless of the method used, the visual confirmation of grease extruding from the narrow end signals that the bearing is fully packed and ready for reassembly.
Reassembly and Final Adjustment
With the bearings fully saturated, the next step involves installing a new grease seal into the back of the wheel hub assembly. The old seal must always be replaced, as it is a wear item that prevents contamination and leakage. Ensure the new seal is seated squarely and evenly into the hub bore. The packed inner bearing is then placed into the hub, followed by the careful installation of the wheel hub assembly onto the spindle.
Setting the wheel bearing preload is the most precise step in the entire process. Incorrect preload is a frequent cause of premature bearing failure. Excessive tightness generates high friction and heat, while too much looseness allows movement that causes impact damage to the bearing surfaces. A common procedure involves tightening the spindle nut to a high initial torque, often around 200 foot-pounds, while rotating the wheel to ensure the bearing races are fully seated.
After the initial seating, the nut is backed off completely, and then re-torqued to a much lower, intermediate value, such as 50 foot-pounds, while rotating the wheel. The nut is then backed off a final, specific amount, often a fraction of a turn, to achieve a slight amount of wheel end play. Manufacturer’s specifications for this final adjustment must be followed exactly. The goal is typically to achieve a minimal end play range, often between 0.001 and 0.005 inches, allowing for thermal expansion and proper operation.