Properly designed and operating in good conditions, the rolling bearing has a long service life. In most cases, it is close to the durability of the whole car. On the other hand, we still encounter the need to replace bearings, and of all kinds. It turns out, that in some vehicles the life of wheel bearings is a problem (e.g.. front hub), in others, one of the bearings of the engine attachment is more likely to fail (e.g.. coolant pumps, timing belt tensioner or alternator). Tend, although rare, gearbox constructions, in which the bearing is damaged. In the chassis, quite often there are problems with the seemingly low loaded bearings of McPherson struts. What are the causes of such a phenomenon, which are usually difficult to associate with inadequate bearing design?
The user would be inclined to look for the cause in the poor operation of the car, but a well-designed bearing arrangement should not be damaged during the use of the vehicle. The life of the bearings of the engine attachment certainly does not depend on the rotational speed and load of the drive unit, the life of the hub bearings is not related to travel speed, and even its dynamics, etc. Of course, can happen, that hitting the curb with the wheel, unluckily we damage the ball or raceway in the bearing, what will initiate the peeling of working surfaces (pitting). Such a strong impact will probably cause serious damage to other suspension components first., at which bearing failure becomes negligible. So what's the problem?
Rolling bearings are most often damaged by:
■ damage to seals and operation in grease with the addition of abrasive silica (Dust, Dust) and water;
■ bending of the bearing journal (even insignificant), which causes increased loads and overheating of the bearing, and as a result, even obliteration;
■ incorrect preload adjustment (applies to such systems, in which this adjustment is made during assembly, e.g.. in pairs of tapered roller bearings);
■ permanent overload of the bearing, what is possible, for example,. in tensioning systems for toothed and V-belts.
As a result, the cause of the failure may not be so much improper operation, careless or unprofessional handling or a design that allows the bearing to be dirty.
So don't be surprised., that car builders are definitely moving away from bearing the hubs of the wheels with pairs of tapered roller bearings, that need to be adjusted during assembly. Such a solution, in terms of strength, nothing can be faulted. In practice, however,, tapered roller bearings can be assembled carelessly, not keeping clean, you can also misalign their initial clearance, and finally apply the wrong grease and install the seals incorrectly. These errors will result in a drastic reduction in bearing life. It is worth emphasizing in particular, what role does the mounting clearance play. No bearing can operate in the long run (at operating temperature) no backlash. Assessing the amount of clearance is difficult and performed indirectly. No backlash, seemingly "beneficial" is the cause of most tapered roller bearing pairs failure. In the common opinion, however, the manufacturer is charged for a bad product. In passenger cars, therefore, the currently closed double wheel bearings reign supreme., which as a whole have a precisely fixed internal clearance (small, and therefore not affecting, e.g.. on the action of brakes), are provided with a load of grease, sufficient for the end of service, and effective seals. From the manufacturer's point of view, their biggest advantage is the compact design and… difficulty of damage during assembly. In any case (not only in the bearing of running wheels), when in a particular car one of the bearings is repeatedly damaged, the reasons should be seen in the minimum, difficult to diagnose curvature of the bearing raceway seat axis, for example, as a result of a neglected impact.