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Guide To Replacing Automotive Bearings
Automobile bearings are one of the key components of important components such as automobile engines. It carries the ultimate load and friction during vehicle movement. Therefore, it is important to maintain and replace car bearings regularly to ensure the smooth operation and safe driving of the car. This article will introduce the precautions for car bearing replacement to help car owners understand and take appropriate measures.
In a typical passenger car that weighs about 3,400 pounds, each pair of front wheel bearings and rear wheel or axle bearings support about 850 pounds, depending on weight distribution and driveline configuration. In the case of a 6,000-pound SUV, each bearing might hold about 1,500 pounds. This load is concentrated on a relatively small bearing surface. These loads don’t even take into account the dynamic loads created by turning. The loads exerted on the bearings are called thrust loads and radial loads. They are the forces that the bearings must withstand when the vehicle turns or brakes. Another unmeasured force is the impact of potholes and curbs.
Overfilling bearings with too much grease can cause the grease to be over-stirred during operation and at high temperatures, resulting in overheating and excessive grease leakage. Overheating occurs because the heat generated cannot be dissipated properly and then builds up until damage occurs. When a bearing overheats and squeezes out grease, the sealing lip can become damaged and “blow out” in the opposite direction.
When bearings wear out, it’s usually due to insufficient lubrication, incorrect installation, or improper adjustment. For repairs to be successful, you must first determine the cause of the previous bearing failure. With sealed hub units, it is not possible to inspect the internal bearings and races. Start by understanding the types of roads they drive on. Also ask what types of loads they typically carry in their vehicles. If a customer overloads the vehicle, bearing damage may be unavoidable. The most common failure mode for bearings is that the bearing on the passenger side of the vehicle fails first. The passenger side bearing is exposed where the most water accumulates on the side of the road. If the bearings on the driver’s side of the vehicle fail first, take a closer look at the bearings on the passenger side, as they may fail shortly after.
Oxidized grease is just as bad as no grease at all.
Burning or oxidizing lubricant may leave a dark coating on the bearing surface. If a bearing overheats, the hot lubricant can break down and cause scratches or even corrosion on the bearing surface. Water and other corrosive elements can also cause this, causing the pavement to peel. Remember that with tapered roller bearings, excessive preload can simulate the same damage. If the bearing becomes very hot, the cage and seals may deform and cause the bearing to lock.
Grease wear.
Grease is a precise combination of oils, thickeners and additives. Grease acts like a sponge to retain and release oil. Oil release properties may become exhausted due to time and temperature conditions. When this happens, the grease wears away.
The bearing may appear to fit, but may not last.
Bearings are precision products that require complex manufacturing processes. Inferior bearings using inferior steel and poorly heat treated will wear and peel prematurely. Inferior steel may contain hard or soft metal inclusions that can cause premature failure. All in all, a cheap bearing may look the same as a high-quality bearing, but it’s what you don’t see that can make the difference between a comeback and a happy customer. Additionally, some cheaper hub units use smaller bearing sizes than the OEM intended. This can also lead to premature failure. Unfortunately, the only way to tell is to destroy the new bearing.
The most important repair tip on serviceable bearings is to invest in a good set of sealed drives. Even slight distortion of the seal during installation can shorten the life of the internal bearings. One may ask, “Why can’t I use an impact wrench to secure the axle nut?” While using an impact wrench may seem easier, it is not recommended. Impact wrenches can damage axle nut threads and shock CV joints during disassembly. It can also create a false sense of security when adjusting a nut or bolt that may be under- or over-torqued. This can make the hub assembly susceptible to failure. Also, in almost all cases, it’s better to use a new axle nut. Some axle nuts cannot be adjusted and are designed to be used only once.
Follow Torque
Always check service information for proper procedures. Over-tightening adjustable tapered roller bearings is a common mistake that can lead to premature failure. The tapered roller bearings at the front of RWD vehicles are never preloaded. They weigh no than 15 to 20 foot-pounds. of torque when turning the wheel to ensure the bearings are in place. Then, loosen the adjusting nut 1/6 to 1/4 turn and lock it in place with a new cotter pin. As a rule, end play should be about 0.001 to 0.005 inches.
Bearing design
For engineers, wheel bearing design and selection can be a balance between durability, cost and fuel economy. Large bearings may be great for fighting potholes and heavy loads, but there’s only so much room in the wheel hub and steering knuckle. Larger bearings may also have increased rolling resistance due to the larger sealing surface. On the other hand, if the diameter of the bearing is too small, it may not be able to handle the load and there may not be enough room for the shaft. Smaller hubs may also lack the stiffness to control flange and rotor motion. Axial spline hubs or face spline hubs are changing the way shafts are connected to hubs and rotors. Asymmetric wheel bearings allow larger wheel and tire assemblies to be installed on vehicles with additional weight or rolling resistance. Both technologies have new service procedures that you should know about.
Correct installation of bearings is very important, but in actual operation it is always easy to go astray and problems arise in endlessly. The reason is that some details were not noticed, causing the bearings to be damaged during installation, and even some damage was not discovered, causing problems during subsequent use of the equipment before the bearings were replaced. Although the cost of replacing a bearing is not high, the cost of downtime is still very high.
How to install car bearings?
Bearings need to be installed in a dry, clean environment and away from equipment that generates metal debris and dust. When it must be installed in a complex environment, contamination should be minimized. Prepare necessary parts, tools and installation equipment before installation. And determine the order of parts installation. Check the machining quality of the shaft, the mating surface of the bearing hole, the shoulder end face, the connecting surface of the groove, and then prepare the bearing.
Press-in method (also called cold installation):
a. Small bearings with transition or interference between the bearing ring and the shaft or shell can be directly pressed into the shaft or shell mechanically or hydraulically. Just apply force on the bearing ring with interference fit. Be careful not to Use a hammer to hammer directly, or use a sleeve and then hammer the sleeve, and gently tap the sleeve to install the bearing into the appropriate position. And when knocking, it should be applied as evenly as possible on the bearing ring to prevent the bearing from tilting or skewing. Force cannot be transmitted through rolling elements, otherwise it will cause crushing on the working surface of the bearing and the bearing will be damaged quickly.
Look at these damaged bearings, do you still dare to do this? This is still visible damage. Those invisible damages will be brought to the equipment. Such bearings will be damaged quickly during use and cause damage. cause greater economic losses.
b. If you want to install the inner and outer rings of the bearing on the shaft and the bearing seat at the same time, you must ensure that the same pressure acts on the inner and outer rings at the same time, press the bearing into the space of the shaft and the bearing seat at the same time, and it must be in contact with the installation tool faces on the same plane. Likewise, force cannot be transmitted through rolling elements.
c. Bearings with separate inner and outer rings can be installed into the shaft and shell respectively, and then installed together. Just pay attention to the alignment. The preload can be adjusted by running out.
Heating or cooling method (also called hot installation):
When the bearing size is large or the interference is large, the required installation force will increase significantly. At this time, the principle of thermal expansion and contraction is required for installation. The temperature difference required for installation between the bearing ring and the shaft or housing depends on the interference size and the size of the bearing fit. Generally, oil bath heating or induction heater is used for heating. The suitable heating temperature is 80 degrees – 100 degrees, and the maximum cannot exceed 120 degrees. (The heating temperature of open bearings shall not exceed 120°C. It is not recommended to heat bearings with seals and dust covers above 80°C. Make sure that the temperature does not exceed the allowable temperature of the seals and grease.)
After the heated bearing is assembled and cooled, the thickness direction will shrink. At this time, the bearing needs to be tightened axially with nuts or other methods to prevent axial clearance.
Bearings with tapered inner holes are installed by interference with the shaft. Generally, they are mostly mounted bearings and self-aligning bearings, and there are also cylindrical bore bearings with an adapter sleeve in the inner ring. The amount of interference after installation is determined by the axial advancement distance of the inner ring on the conical shaft diameter, adapter sleeve or withdrawal sleeve. The greater the advancement distance on the conical mating surface, the smaller the radial internal clearance of the bearing. The amount of interference can be determined by measuring the clearance reduction or the axial advancement distance. When installing, first measure the bearing radial clearance. During the pressing process, just check that the clearance reaches the required value.
For small and medium-sized bearings, you can use a bearing installation tool or preferably a locking nut to push the inner ring into the appropriate position on the conical shaft diameter. When using an adapter sleeve, use a socket nut that can be tightened with a hook or impact wrench. Use the bearing installation tool or the end plate to push the withdrawal sleeve into the bearing inner hole. Larger bearings require greater force to install, so hydraulic nuts should be used.
For single and double row angular contact ball bearings, tapered roller bearings, and thrust bearings, the final stage of installation is to adjust the bearing clearance. It needs to be accurately adjusted according to the installation structure, load, operating temperature, and bearing performance. Adjustment of clearance can be measured with a dial indicator or adjusted by experience.
Car bearing maintenance
1. Regular lubrication: Proper lubrication is a key measure to maintain automobile bearings. Car owners should lubricate bearings according to the manufacturer’s recommended maintenance intervals. The lubricant should be a cleaning oil of appropriate grade and viscosity to ensure its compatibility with the bearing material. Bearing lubrication should follow the correct lubrication method and amount to ensure effective coverage and protection of the bearings.
2. Pay attention to the usage environment: Cars are susceptible to pollution and corrosion, so car owners should try to avoid using their vehicles in harsh working environments. Especially when driving in dusty, sandy, high temperature or humid environments, the maintenance and cleaning of automobile bearings should be strengthened. Regular inspection and replacement of components such as the air intake system and air filter can effectively reduce bearing contamination and corrosion.
3. Avoid overload and vibration; during driving, try to avoid the impact of overload and severe vibration on the bearings. Car owners should reasonably adjust their driving style and reduce sudden braking and acceleration to reduce the load on the bearings. In addition, good maintenance of the car’s suspension system can also reduce the vibration and impact of the vehicle on the bearings.