The Effects of the Wheel Bearing and Mating Parts to Rotor Runout and Runout Variation

During validation of a new brake lining on a light duty truck application, the brake rotor exhibited high lateral runout on the friction surfaces. As the engineering team investigated the issue more carefully, they noticed the rotor lateral runout was also changing from revolution to revolution. The team ran testing on multiple light pickup vehicles and found differences in the amount of rotor runout variation. The rotor lateral runout and runout variation can cause vibration and pulsation of the passenger seat and the steering wheel. To identify the root cause of the high level of rotor lateral runout and runout variation, measurement data was collected and analyzed from the vehicle level test. During further analysis, some of the runout variation corresponded to a wheel bearing internal frequency. The bearing internal geometry was studied to confirm what factors affected the runout variation. The team also conducted testing to see how the mating components may have affected the wheel bearing. In addition to the vehicle testing, fixtures were built to perform brake corner bench testing. This testing showed that both the total runout and runout variation increased as more mating components were added. Brake corners from two different vehicles were bench tested. The major difference between the vehicles was the mounting location of the splash shield. On one vehicle the splash shield is mounted (sandwiched) between the knuckle and the bearing’s outer ring flange and on the other vehicle, the splash shield is directly mounted with screws to the knuckle (not sandwiched). Splash shield distortion due to compression near the knuckle bolts and the bearing outer ring contact surface, caused the larger total runout value and the higher variation. The study also proved that continuous assembly/disassembly will increase the distortion on the mating parts, which leads to the greater total runout and variation values.