Wheel bearings can be some of the most misunderstood components of a car, and the confusion can run the gamut from technicians all the way through to the service department. But, without a doubt, motorists will have the most questions.
Much of this confusion stems from the types of bearings that were used in automobiles and were commonplace all the way up into the 1990s. Primarily, I’m referring to the tapered roller bearing. Cleaning and repacking these bearings was such a common service that most vehicle owners came to expect it, just like the 3,000-mile oil change and regular tune-up.
Even to this day, when a customer hears “wheel bearing,” many of them expect an inexpensive service or an inexpensive part. Many aspects of automotive technology – airbags, antilock braking systems and tire-pressure monitoring systems, for example – are well-known. But, wheel bearings always have remained in the shadows, leaving us as automotive professionals having to explain them.
While most counter pros and technicians are familiar with the fact that sealed wheel bearings and bearing-hub units account for the majority of wheel bearings on cars today, many vehicle owners are not. Nor are they familiar with the different types and how they relate to the overall design of the steering and suspension systems.
At the most fundamental level, all wheel bearings are simply roller bearings – meaning they contain rolling elements. The different types of roller bearings include cylinder roller bearings, tapered roller bearings, barrel roller bearings, needle bearings and ball bearings. The rollers are trapped in a cage to keep them in place, and then located between an inner and outer ring. Each ring has a groove called a race, in which the rolling elements roll.
The tapered roller bearing is one of the most well-known and recognized types of bearings, but the other types were commonly used for axle bearings or applications where a gear oil provided lubrication as opposed to grease.
Wheel bearings take an incredible amount of abuse due to the different types of loads in vehicles, such as cornering, acceleration, braking, potholes and the weight of the vehicle. These factors, along with the increased demands of automotive engineering, created the need for bearings that offer lower maintenance, less weight, reduced friction, less noise and longer service life.
A compact bearing unit, known to many technicians and counter pros as a “sealed wheel bearing,” was the first major technology advancement. This style of bearing was constructed of two sets of caged rollers: a one-piece outer ring/race with two inner rings/races. The entire unit was pressed together, lubricated and sealed, creating a maintenance-free bearing. These are known as Generation
With minor variation in design, Generation 1 bearings were pressed into a steering knuckle and held in place by a type of snap ring. A wheel hub was then pressed into the bearing and an axle shaft would slip through the hub (splines on both would mate together), ultimately transferring power from the shaft to the wheel. Early front-wheel-drive (FWD) cars are where most of us saw the initial influx in the use of Generation 1 bearings.
As ABS and traction-control systems came onto the scene, these bearings also would house a sensor ring or pick-up. Installing these bearings was sometimes a time-consuming process, and caution had to be taken to support the inner and outer rings properly when finally pressing the bearing and hub in place. If the bearing contained a sensor ring or pick-up, care had to be taken to install it on the correct side, as the bearing appeared the same at a quick glance, in many cases.
A Generation 2 bearing is a compact bearing unit as well, but with one flange already pressed in place. The flange can be either a wheel hub or a mounting flange, and they have been used for both driven and non-driven axles. A common use for some of the first Generation 2 bearings was on the rear of a front-wheel-drive car. The Generation 2 bearing would slip onto the stub axle and be held in place by a nut. These bearings also came with or without ABS-sensor rings, depending on the application.
A Generation 3 bearing, also the same compact bearing unit, is constructed with two flanges. One is the wheel hub, and one is a mounting flange to bolt it to the steering knuckle. These also can come with or without ABS-sensor rings, and, in many cases, the entire sensor is built into the bearing assembly. Generation 3 bearings are the most common type used today and are used on driven and non-driven axles. Theoretically, Generation 3 bearings are among the easiest to install, but rust and corrosion can make it very difficult at times. Regardless of the generation of bearing, following the recommended service procedures is critical for maximizing the lifespan of the new bearing (and preventing a customer comeback). Hub-bearing removal and installation, for example, is a process that requires strict adherence to the service information, particularly the torque specifications. Deviating from the recommended procedures can leave the hub assembly vulnerable to premature failure, and create an unsafe situation for the driver and passengers. It also can lead to unnecessary returns at the parts counter.