The function of the rear wheel bearing of a car
The main function of the hub bearing is to bear weight and provide precise guidance for the rotation of the hub. It bears both axial and radial loads and is a very important component. The traditional bearings used for car wheels are composed of two sets of tapered roller bearings or ball bearings. The installation, oiling, sealing and adjustment of clearance of the bearings are all carried out on the car production line. This structure makes it difficult to assemble in car manufacturers, costly and unreliable. Moreover, when the car is maintained at a repair point, the bearings also need to be cleaned, oiled and adjusted. Hub bearing units have developed on the basis of standard angular contact ball bearings and tapered roller bearings. They integrate two sets of bearings into one, featuring good assembly performance, no need for clearance adjustment, light weight, compact structure, large load capacity, pre-installation of grease as sealed bearings, no need for external hub sealing, and no maintenance required. They have been widely used in automobiles There is also a trend of gradually expanding its application in heavy-duty trucks.
In the past, the hub bearings of cars were most commonly used in pairs as single-row tapered roller or ball bearings. With the development of technology, car hub units have been widely used in cars. The application scope and usage volume of hub bearing units are increasing day by day, and they have now developed to the third generation: the first generation was composed of double-row angular contact bearings. The second generation has a flange on the outer raceway for fixing the bearing, which can be simply fitted onto the axle and fixed with a nut. It makes the maintenance of cars easier. The third-generation hub bearing unit adopts a bearing unit in combination with an anti-lock braking system (ABS). The hub unit is designed with an inner flange and an outer flange. The inner flange is fixed to the drive shaft with bolts, while the outer flange installs the entire bearing together. Worn or damaged hub bearings or hub units can cause inappropriate and costly failures of your vehicle during driving, and even pose a threat to your safety.
Please pay attention to the following matters when using and installing hub bearings:
To ensure safety and reliability to the greatest extent, it is recommended that you frequently inspect the hub bearings regardless of the vehicle's age - pay attention to early warning signs of bearing wear: including any friction noise during rotation or abnormal deceleration of the suspension combination wheels when turning. For rear-wheel drive vehicles, it is recommended that the front hub bearings be lubricated when the vehicle has traveled 38,000 kilometers. When replacing the braking system, check the bearings and replace the oil seals.
If you hear an abnormal noise coming from the hub bearing area, the first and most important thing is to find the location where the noise occurs. There are many moving parts that may produce noise, or it could be that some rotating parts have come into contact with non-rotating parts. If it is confirmed that the noise is from the bearing, the bearing may be damaged and needs to be replaced.
Because the working conditions that cause the failure of the bearings on both sides due to the front wheel hub are similar, it is recommended to replace them in pairs even if only one bearing is damaged.
Hub bearings are rather sensitive, and in any case, the correct methods and appropriate tools must be adopted. During storage, transportation and installation, the components of the bearing must not be damaged. Some bearings require a relatively large pressure to be pressed in, so special tools are needed. Be sure to refer to the car manufacturing manual.
When installing bearings, they should be done in a clean and tidy environment. Fine particles entering the bearings will also shorten their service life. It is very important to maintain a clean environment when replacing bearings. It is not allowed to strike the bearing with a hammer. Be careful not to drop the bearing on the ground (or handle it improperly in a similar way). Before installation, the condition of the shaft and bearing housing should also be inspected. Even slight wear can lead to poor fit, thereby causing premature failure of the bearing.
For hub bearing units, do not attempt to disassemble the hub bearings or adjust the sealing rings of the hub units; otherwise, the sealing rings may be damaged, allowing water or dust to enter. Even the raceways of the sealing ring and the inner ring were damaged, resulting in the permanent failure of the bearing.
There is a magnetic thrust ring inside the sealing ring of the bearing equipped with the ABS device. This thrust ring must not be subject to collision, impact or contact with other magnetic fields. Before installation, remove them from the packaging box and keep them away from magnetic fields, such as the electric motors or power tools in use, etc. When installing these bearings, observe the ABS alarm needle on the dashboard through road condition tests to adjust the operation of the bearings.
For hub bearings equipped with ABS magnetic thrust rings, to determine which side the thrust ring is installed on, you can bring a small and light object close to the edge of the bearing. The magnetic force generated by the bearing will attract it. When installing, point the side with the magnetic thrust ring inward, directly facing the sensitive components of the ABS. Incorrect installation may lead to the failure of the braking system's function.
Many bearings are sealed and do not require grease throughout their entire service life. Other unsealed bearings, such as double-row tapered roller bearings, must be lubricated with grease during installation. Due to the different sizes of the inner cavities of the bearings, it is difficult to determine how much grease to add. The most important thing is to ensure that there is grease in the bearings. If there is too much grease, when the bearings rotate, the excess grease will seep out. General experience: During installation, the total amount of grease should account for 50% of the bearing clearance.
When installing lock nuts, the magnitude of the torque varies greatly due to the differences in bearing types and bearing housings.
During the maintenance process, it is often found that some vehicles have a relatively loud driving noise. After checking, there is no abnormal wear on the tires. When turning the wheels on the lift, there is no obvious abnormal noise. This phenomenon is often caused by abnormal damage to the hub bearing. The so-called abnormal refers to the bearing damage caused by installation reasons. The front wheel bearings of a car are generally double-row ball bearings. When installing the bearings, if a hammer is used to strike them or the inner ring of the bearing is pressed when installing them into the bearing housing, it will cause damage to the raceway on one side of the bearing. When a vehicle is in motion, noise is produced. However, when the wheels are off the ground, due to the better side of the raceway, no obvious noise can be heard. Correct installation and operation are the key to the long service life of bearings.
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