A popular discussion about taper roller bearing (TRB) products involves methods for preloading and adjusting them. Manufacturers and mechanics are always looking for better ways to increase accuracy, reduce complexities, and improve serviceability.
There is a direct and indirect method for preloading, but the ultimate goal is to have a total axial load on the taper roller bearing while it’s at rest. The direct method can measure axial force on the bearings during preload or can measure axial displacement. The indirect method uses a measurement of the axial load and the torque used to rotate it.
Many technicians focus on the direct method with its spacer/shim arrangement. With this option, the bearing and housing dimensions are measured and the shim size is calculated to give you a dimensional offset. You are displacing the bearings by a known value. This is a very accurate method, but can only be as precise as the shim tolerances and thickness.
Many taper roller bearing applications are set up with the indirect measurement method. Likewise, axle and PTU pinions, final drives and more can all be set up with this version. It is less accurate because the preload relationship versus torque isn’t as accurate as the preload relationship versus the axial displacement. You can expect up to a 20 percent scatter range when using this method, but it is a manageable tradeoff for high production and reasonable serviceability.
You can add/remove accuracy with this system as needed. For example, if you need higher precision, you can measure the individual bearings for torque and then set it up.
Many times, you can use the various pairs and different parts with preloaded/matched sets that already use ground shim arrangements. In most cases, it will hit the best preload each time, but unique assemblies may not accommodate such products and most factories still prefer to preload them before sending them to auto-part shops.
There is no perfect method to preload your bearings. In most cases, the method used is based on what’s possible with the surrounding components and bearings, as well as the resources available, budget, factory capability, manpower, and serviceability. The facility you choose should be able to adjust their method and accuracy based on your needs.
Likewise, the systems architecture may require that you use a particular method. While a bearing-tightening-nut works well for many applications, it may not function in a power takeoff unit or manual transmission.