|New hub units may exhibit rough feel when rotated by hand, a characteristic common with today's high performance products. SKF reports the rough or coarse feel of some new hub units if they are rotated by hand before installation and explains why these conditions are normal for technicians to experience.
In recent years there have been concerns about new hub bearings being rough or difficult to rotate. Many technicians inspect a new replacement hub bearing visually and by rotating the assembly once or twice by hand.
During the inspection process, it is not abnormal to feel a rough, coarse sensation as the two halves of the hub are rotated. This condition is not an indication of a defective bearing; these hub units should not be returned as suspected defective parts.
This condition is caused by the premium grease SKF uses in many of its bearings, especially in hub bearings. SKF uses GHG grease that provides a significant advantage over other standard greases.
SKF GHG contains many performance-enhancing additives, some of which are in the form of soft crystalline structures when the grease is new. These crystalline structures can create a rough, coarse feeling when the hub bearing is first turned by hand, before the bearing has experienced significant rotation.
These additives are important to optimum wheel bearing performance and include anti-brinelling and extreme pressure performance enhancers and solid lubricant components. This advanced technology grease chemistry improves bearing performance from many aspects, ranging from protecting against bearing damage during vehicle transport to maintaining proper lubrication conditions during high load/low speed operation to lubricant stability at elevated operating temperatures.
Even though the bearing may feel rough when it is initially rotated by hand, after rotating on the vehicle for a few minutes, the soft crystalline structures in the grease will break down into finer structures, and the bearing will rotate smoothly. There is no detrimental effect of the SKF GHG grease run-in. This is the normal and desired behavior of this type of grease.
Another item that may contribute to a hard turning hub bearing is the seal. In some hub bearings, the seals also have more interference with the bearing. Once the bearing is rotated for a few minutes, the bearing will gradually turn freely. This is a normal situation.
As a reminder, Generation 3 hub assemblies need to be fully preloaded/seated with the correct torque in order to operate properly. Without the proper bearing seating on a hub assembly, the bearing may have a feeling of roughness when turning it. The rough feel is more noticeable in bearings that are preloaded from the factory, as many of these newer generation hub units are preloaded. Always remember to follow the OE manufacturer's recommended torque specifications and procedures when installing the axle nut. This will create the correct preload for the hub assembly.