Although modern drive joints are by no means a nuisance to drivers and car repair shops, however, they require some attention. The most important thing in each joint is lubrication. Paradoxically, even in elastic joints, of which a substantial part, i.e. vibration-absorbing rubber, hates petroleum products. It is possible to approximate the end of the life of the elastic joint, allowing this to happen, that grease or oil from closely located mechanisms will get on it. Flexible joints can also be harmed by improper installation (non-grey mounting) or uneven prestress of the entire device. Then, during work, there will be a rapid "fatigue" of too intensively working rubber material. Of course, the damage can be caused by sudden overload, which, however, rarely happens during the normal operation of vehicles.
All other types of joints require very intensive and efficient lubrication, more or less like this, what is the share of rolling bearings. Joints are usually constructed in this way, that the grease load is to be sufficient for the whole, very long service life. Only cross joints are sometimes equipped with lubrication points, which can be found almost exclusively in the shafts of large machines and trucks.
Lubrication is particularly important for ball joints, where the drive torque is transmitted through the linear (even point) pressure of individual balls on the surface of the grooves, so the peak values of unit pressures can be enormous. At the same time, with the deviation of the rotating shafts, the balls travel all the time along the grooves. Therefore, special semi-liquid lubricants are used in ball joints, similar properties to bearing properties, but thanks to the addition of molybdenum disulfide significantly increasing the resistance to mashing. Despite this, over time, the surface of the joint grooves may wear out. This consumption is usually the highest there, where the balls stay most often (when driving straight ahead), that is, more or less in the middle of the groove. The effect is very characteristic: when the shafts are not tilted (straight ahead riding), the clearance in the joint is greater than the nominal, but it works satisfactorily. However, after turning the wheels during acceleration from the joint, there is a loud rattle of balls jumping over uneven grooves. Such a signal, usually coming from the wheel on the inside of the bend, indicates the need to replace the joint. A "crackling" ball joint can break into pieces at any time.
The cause of accelerated wear of the joint is usually dirt on the grease, as a result of damage to the rubber cover. So the problem in contemporaries, well made joints is constantly rubber.
