With most types demanding attention only when they start to fail, Rob Marshall discovers that there is more to hub bearings than keeping the wheels on.
Subjected to the axial forces of cornering, radial forces from acceleration and braking, let alone sudden shock loads introduced by poor road conditions, or driver error, it is remarkable that wheel bearings can last in-excess of 100,000 miles, especially as most types require zero routine maintenance. FAG, one of Schaeffler’s brands and an original equipment supplier to vehicle manufacturers, explains why we should not be so surprised, because development of a new bearing can take anywhere between two and five years and must undergo every imaginable extreme test, both on-and-off the vehicle, before being put into production.
GETTING THE PART RIGHT
Considering the effort that OEM suppliers exert in making these safety critical parts achieve their design objectives, the aftermarket needs to be sensitive about not only selecting quality replacement parts but also the fitting methods. Should you get either of these wrong, the reduced lifespan of the replacement wheel bearing could be the least of your worries.
Understandably, the quality aftermarket component providers realise this and stake their reputes firmly on quality. Like FAG, NTN-SNR Bearings supplies both car manufacturers and the aftermarket; it states that there are many factors that result in a wheel bearing, which will be safe and long lasting. Yet, non- OEM suppliers are keen to emphasise quality, too. febi bilstein emphasises that its internal certified quality management tests match OE quality requirements, which assess precision, fit, dimensional stability, material quality, tensile strength and hardness.
First Line has its bearings manufactured to OE specifications, tested to seven different criteria, with materials and manufacturing processes being controlled tightly, allowing for full traceability throughout the production processes. Like First Line, Comline works exclusively with ISO compliant factories but the company conducts its own regular in-house quality testing in addition to those performed by its manufacturing partners.
DODGING THE BULLET
febi bilstein warns that counterfeit alternatives are becoming more prevalent, where both the wheel bearing’s appearance and its packaging are copied but the important technical details are not replicated as faithfully. NTN-SNR confirms that these low-grade substitutes do not meet the strict specification of the equivalent OE quality bearing. Technical concerns include incorrect tolerances and sub-standard materials. Poor build quality is reflected in poor sealing, which permits the often unsuitable grease to leak out, and that is presuming that water ingress does not cause seizure beforehand. From a fitting perspective, NTN-SNR reports that counterfeit bearings tend not to be made to correct dimensions, which makes them harder to install, risking damage to hubs and stub axles during the fitting procedure.
First Line told AT that these situations occur, because these bearings tend to be produced by manufacturers with little engineering or technical knowledge, using raw materials of an unknown quantity. FAG highlighted that some low-quality wheel bearings have their ABS encoders glued into place, rather than integrated into the seal. These either fall off, or do not provide an accurate enough signal for the wheel speed sensors. FAG concludes that,
“The wheel bearing is a safety critical item. By fitting a cheap copy bearing, you are putting the occupants of the car and other road users at risk. It is a gamble – like Russian Roulette.”
TIP OF THE ICEBERG
When excessive noise, or play, indicates a wheel bearing needs to be replaced, look for reasons why the bearing has failed. Admittedly, it is not always easy to establish how many times the driver has struck potholes, or driven through floods, but be aware that wheel bearing life can also be affected by other components.
FAG reveals that the wheel bearing acts as a heatsink and changing associated components for those of a different specification risks placing them under extra stress. febi bilstein adds that fitting inferior quality braking parts, such as discs, can introduce excessive vibrations into the bearing. First Line explains that this can lead to ‘brinelling’, where the rolling elements (balls or rollers) impact and dent the bearing’s raceway surface(s), accelerating wear levels.
HELPING YOU TO DO YOUR JOB
Aside from the safety and liability considerations of buying suitable quality parts, ensure that a supplied wheel bearing kit includes all of the necessary parts, such as new hub nuts and seals/covers, so that you can complete the repair properly snap-ring/retaining clip. In cases where a bearing fits into a steering knuckle housing, it can be difficult to apply force to the outer race, because it is made inaccessible without having to wait for extra parts to arrive. Access to technical data, such as Schaeffler’s REPXPERT, should be used to not only ensure the correct part number but also to access fitting instructions and torque specifications. As even the best quality bearing can be damaged by incorrect fitting, consider the need for dedicated equipment. Steve Prince of Pichler Tools highlights that technicians can struggle to not only fit Generation Two wheel bearings but they can also fail to identify them correctly, because not all types are fitted with a snap-ring/retaining clip. In cases where a bearing fits into a steering knuckle housing, it can be difficult to apply force to the outer race, because it is made inaccessible by the integral road wheel mounting hub being in the way. Applying pressure to this flange instead of the bearing outer ring causes forces to be transmitted though the inner bearing ring, then to the outer ring via the rollers.
Aside from any physical damage that this might cause to the main bearing components, the weather seal can be compromised, risking water ingress. The correct method is to apply force to the outer bearing race with the dedicated tool. Pichler Tools’ Universal Gen2 Wheel Bearing Kit not only performs this duty but adjusts to accommodate the different bearing sizes, up to (and including) the Mercedes Sprinter commercial vehicle. Not only does the tool ensure correct fitting but it also can be used to press-out the old bearing, which can save workshop time too, by negating the need to remove the ABS sensor.
TOP 10 TIPS FOR BEARING FITTING
- Avoid using a hammer to fit the bearing, such as installing one to a stub axle. This causes brinelling (damage to the raceway, caused by impact from the rolling elements), which shortens the bearing’s service life.
- Do not use an impact gun to install the hub nut. Not only can this damage the bearing but it also makes it impossible to establish the torque applied. Gather the appropriate torque specifications from the part supplier, or from the OEM fitting instructions.
- Where taper bearings (Generation 0) are installed on older vehicles, do not forget to grease them adequately and avoid contaminating the lubricant. Ensure that the front hub bearing end-float is adjusted to the manufacturer specifications (as pictured), because overtightening will shorten bearing life considerably.
- Ensure that the mounting surfaces are clean, free from corrosion, or other debris, before fitting. Contamination in and around the wheel bearing can cause it to fail.
- Ensure that all threads are clean and in good condition.
- Should any be reusable, check that any fixings are in good order. Be wary if any parts (such as hub nuts) are for single use only and that they are renewed accordingly. Split pins, or similar locking systems, should be installed correctly prior to the vehicle being driven.
- Ensure that the bearing is installed correctly, not backwards, or at an angle (which cracks the inner ring), and that the hub/stub axle is not damaged.
- Be careful with bearings containing active ABS sensor rings, which must be protected and not placed near anything magnetic. The encoder face must not be laid on a workshop bench, which may damage, or contaminate it. Do not subject them to shocks, either.
- Use bearing installation tools, especially for Generation 2 bearings, onwards. Where a snap ring (or retaining clip) is fitted, such as on certain VAG applications, it must be located accurately in the groove on the hub. Using a workshop press is not a suitable alternative.
- Check that any wheel speed sensors are clean, in good order and installed correctly.
BEARING EVOLUTION – AN OVERVIEW
Wheel bearings have evolved, because cars have become heavier, more powerful and have boasted increased wheel sizes. Pressures to reduce weight and drag, to help the carmaker lower CO2 emissions and fuel consumption, come with the need to reduce time and costs at the vehicle assembly stage. To date, therefore, you will encounter four different generations of bearing, all of which dictate different handling, removal and fitting methods. As always, follow the fitting instructions for the appropriate application carefully.
‘Generation 0’ are taper roller bearings, with separate inner and outer races and seals. They are used on many classic and retro cars, especially for the non-driven wheels. The most common applications are VW-Group applications throughout the 1990s and early 2000s, Vauxhall applications up to 2000, RWD Ford Transit, Mercedes-Benz Sprinter/VW LT
to 2006 and the Citroen Relay/Fiat Ducato/Peugeot Boxer to 2002.
‘Generation 1’ combined all of the Generation 0’s components into one assembly. As this design is pre- lubricated and sealed, they are maintenance-free, because it was not necessary to check the play/end- float periodically any longer. Tightening the hub nut sets the required bearing end-float. Most types are secured with a circlip and even a snap ring, in some circumstances.
‘Generation 2’ type bearings possess a flange that acts either as a mounting point for the road wheel, or as a mounting point to the axle carrier. The centre can be splined, for driven axles. The main advantages are a reduction in the number of individual parts and enhanced rigidity. Yet, be aware of the special tools required to press the bearing into the bearing seat, using the outer ring. A snap ring (or retaining clip) may be fitted instead of a circlip but this is not true for every application.
‘Generation 3’ bearings possess two flanges, rather than just one. Some types may be equipped complete with ABS sensors. An advantage to the aftermarket workshop is that this design does not require any special tools to install them.