A torque wrench is an essential tool when it comes to installing wheel bearings. Here are the top 10 tips to remember about these tools and procedures.
- CHECK RECOMMENDED TORQUE PROCEDURES AND SPECIFICATIONS
It is almost impossible to give a general specification or torque range for a wheel bearing axle nut. There can be significant differences depending on bearing type and housing. Always check the service information for the correct procedure.
Hub units may require many steps to adjust the final torque of the axle nut. On some hub units with factory set preload, the axle nut can only secure the knuckle in the bore. On other hub units, the final adjustment is to set the load paths for races and rolling elements. Torque specs depend on bearing size, axle diameter, and many other factors like axle nut style.
Wheel bearing manufacturers may use a different style nut that is included with the bearing. This nut may have a different torque specification – lower or higher – than the value stated in the service information. Some manufacturers include this information in the box.
Even if you are installing a set of tapered roller bearings, it is worth looking at the service information. Not all procedures and specifications are the same, and the method you learned in school or from your dad may not work on some vehicles.
- IF HE SAYS “ON THE COURT”, DO IT ON THE GROUND
Many vehicles require the wheels to be on the ground for final tightening of the axle nut to specification. This ensures proper mating of the split inner rings of the bearing needed to achieve the proper internal clearances. However, jamming a screwdriver into the rotor fins and bracing it against the caliper bracket may not yield the same results. For specific instructions, refer to the vehicle manufacturer’s service information.
- USE A NEW NUT / COLT PIN*
Some hub units and wheel bearing assemblies come with a new nut in the box. In effect, the nut deforms to secure the hub to the axle. In these applications, a new nut should always be used when installing a hub. Reusing the old nut could cause the nut to loosen during vehicle operation.
- CLEAN AXLE SHAFT BEFORE INSTALLATION
Clean and inspect the axle shaft before installing a new hub assembly. Use a fine file, wire brush, emery cloth, or whetstone, as appropriate, to remove debris, nicks, or burrs from the splines. You can apply a light coat of oil to the splines. But do not use lubricants on the threads or washers. This can reduce friction on the threads and cause the nut to be overtightened.
- DO NOT USE YOUR TORQUE WRENCH AS A SOCKET WRENCH
Use a torque wrench to apply a specific torque value during the final assembly process. Do not use a torque wrench as the primary means of tightening or loosening fasteners. Also, lower the torque wrench before putting it back in your toolbox.
- DO NOT USE IMPACT
Although it may seem easier to use an impact wrench, it is not recommended. OEM and bearing manufacturers always recommend using a torque wrench for installation. Using an impact to “drive down” the axle nut can cause the assembly to be over-tightened. However, when dismantling, it is possible to use an impact. First, loosen the axle nut with a breaker bar if possible. Using this method can prevent damage to the steering knuckle or CV joint.
- REPLACING A DAMAGED WHEEL HUB FLANGE BEFORE ASSEMBLY
When replacing a press-in type wheel bearing and hub flange, it is important that all parts of the wheel end work together correctly after reassembly. A hub flange with a damaged shoulder that contacts the inner bearing can cause inconsistent torque values and lead to failure down the road. Wheel hub flanges for most applications are available from many sources.
- DO YOU TRUST YOUR TORQUE WRENCH?
For some hub units, the final torque specification can range from 150 to 350 ft/lbs depending on the application. Accurate tightening of the nut is critical in defining bearing load paths. But you have to trust your torque wrench.
Torque wrenches designed for lug nuts typically have an upper limit of 190-200 ft/lbs. Even if a hub’s final torque is 185 ft/lbs, you might be at the limit of your torque wrench’s accuracy. A torque wrench is most accurate in the middle, and almost all torque wrenches are least accurate at the ends of its wrench scale range. So if the final torque is 200 ft/lbs, you better use a torque wrench with a 300 ft/lbs limit.
How to tell if your torque wrench is accurate? Some tool carts are equipped with a torque wrench tester that can help locate a faulty torque wrench. You should test at least several torque settings, including the highest and lowest settings. It is not uncommon to find a wrench that will be accurate at 50 ft/lbs, but significantly inaccurate at 25 or 150 ft/lbs. If the accuracy is poor, you should send it in for calibration rather than buying another torque wrench.
- USING AXLE NUT SOCKETS
Axle nuts are usually recessed into the flange. The nut will normally be 29mm or larger and can be a six or 12 point hex. In some cases, the pin will protrude, preventing the use of a shallow socket. Tool makers make sockets specific to axle nuts.
Using these sockets can prevent backlash and damage the nut. They can also increase the accuracy of the torque wrench by fully engaging the nut.
- DON’T FORGET OTHER TORQUE SPECIFICATIONS
Most hub units are attached to the suspension knuckle using three or four fasteners. These fasteners have their own specifications and torque procedures. Some of these bindings are torque-yielding and cannot be used a second time because they have stretched. Additionally, some fasteners use thread locking compounds that must be removed and reapplied.