Bearing Diagnostics: Brinelling/Non-noise Failures
In the past, serviceable bearings were maintained between 25,000 to 35,000 miles, and the inner workings could be inspected and replaced if damaged. Today, the average life of a sealed bearing is 85,000 to 100,000 miles, but they can fail sooner without making any noise. The last signs of failure are noise and play. These are symptoms of a problem that started a long time ago, but the bearings make no noise and cause vibrations and problems with the brake system. Pulling on the wheel at the 6 and 12-o’clock positions can test bearings, but that only catches the really bad ones. New techniques are easier, and can catch bad bearings sooner.
Causing Bearing Problems
Loads being put on the bearings when a vehicle hits a curb, pothole, or other object can exceed the material’s hardness limit. When this happens, the damage is called Brinelling. The result of the damage is a permanent dent called a Brinell Mark. Brinell marks may or may not cause the bearings to make noise immediately, but as the marks keep rolling, it can damage the entire bearing. If the impact changes the bearing’s pre-load, it can cause more noise and damage.
The wheel bearing’s flange is a direct indicator of the health of the bearing. All flanges have runout, but more and more manufacturers are going to a 0” runout specification because, any runout in the flange is magnified by the rotor. Even a very small amount of runout can cause problems over time. Runout can sometimes be corrected by using the brakes, but it removes material from the rotor. If that is the case then a plate can be put between the flange and the rotor to fix it, but if that doesn’t fix it, the flange/bearing must be replaced.
Most vehicles with hub units use tone rings located between the inner bearing races. The air gap is very precise, so if there is play in the bearing, the ABS/ESC computer will pick up the signal changes and disable the system and illuminate the ABS light. If a vehicle has these symptoms, the bearing should be replaced even if there is no noise or play.
When replacing the bearing, it is a good investment to use a high quality bearing made from harder materials that won’t Brinell under hard impacts. Replacement hub units may have special grease that prevents damage during shipping but when it is installed the grease breaks down and the hub functions normally. It is not recommended to use an impact wrench for installing bearings and hub units. An impact wrench can damage the axle nut threads and shock the CV joints while also over torque the nut leaving it susceptible to failure. Also, in almost all cases, a new axle nut should be used.