Spring must be here, because baseball is in the air! Spring training is refocusing players on the basics of the game in hopes that what they relearn now will result in a winning season. Perhaps the timing is right to refocus on the basics of wheel installation, a procedure that almost every commercial tire service technician performs each workday.
While there is no "World Series" to win, something even more important is at stake: your customers' safety, the safety of the motoring public, retention of your fleet accounts and your company's liability costs.
If a wheel you install comes off a truck while it is traveling down a busy highway, the well-being of all of these is at risk.
Let's examine a few of the often overlooked or forgotten "basics" and see if there isn't something here that can improve your "game."
Before installing a tire and wheel assembly on a vehicle, the first thing you need to do is clean all of the mating surfaces. Why? Because dirt and rust will prevent you from attaining the proper level of torque needed to hold the system on. In fact, it can cut the amount of clamping force attained in half!
Even if the correct clamp load is attained, dirt and rust can be dislodged while the vehicle is in operation, and this will result in loose wheels. So, cleaning is essential.
Use a wire brush to clean the base of each stud, as well as the threads, to remove any rust or foreign material that could bind up the wheel nuts. Wire-brush the mounting faces of the brake drums and wheels to remove loose paint, dirt and debris, too.
If you are mounting hub-piloted wheels, also make sure the center hole of the wheel is clean so it fits easily onto the hub pilots.
While you are cleaning all these parts, inspect the studs for shiny or damaged threads that indicate stripping. Replace any studs you find like this, as well as any studs and nuts that are rusty or corroded.
Also make sure the wheel mounting faces are straight and do not have cracks, wallowed holes or worn ball seat chamfers.
Questions about lubrication puzzle seasoned professionals and rookies alike. The only lubricant that should be used in wheel-fastening systems is 30-weight oil. In hub-piloted systems, two drops of oil should be placed between the nuts and flanges, and two drops on the last 2 or 3 threads at the end of each stud.
This oil will restore the original friction level between the nut and the washer, as well as the stud, so that you get the same clamp force as new nuts and studs. Spin the nuts on the flanges and make sure they turn smoothly. If they don't, replace them.
To prevent the wheels from sticking to the pilots, it is acceptable to take your finger and wipe the pilots with either oil or Freylube. It is vital that no lubricant gets smeared on the mounting faces of the hub, drum or wheels. If this happens, the whole assembly will be loose!
Many technicians use anti-seize compounds to lubricate studs and nuts to prevent them from freezing together. While their intentions are good, they are causing more harm than they realize. These compounds increase the clamping force of the studs and nuts significantly and cause the studs to break or, even worse, "yield."
Studs actually stretch a bit as they are put into tension when the nuts are installed. When the nuts are removed, the studs spring back to their original length. When they are over-stretched due to over-torquing, they "yield," which means they do not spring back. The result is a loss of tension.
This is worse than broken studs, because you can't "see" yielded studs, so you don't know that the system is loose. Often times, too, anti-seize compounds get smeared all over the place, since they are usually brushed on, and create loose wheel systems that way.
Instead of lubricating inner and outer cap nuts, replace them when you find paint buildup, damaged or deformed threads, or corrosion. Otherwise, the next time the wheels are removed, these nuts will be frozen.
Bolting the wheels on the vehicle is not rocket science, but you'd be amazed at the number of technicians that "strike out" in this area.
To hit a home run every time, the nuts should be installed finger-tight at the 12 o'clock and 6 o'clock positions, followed by the rest of the nuts. Then they should be snugged to about 50 ft.-lbs. following a criss-cross sequence. The final step is to tighten all the nuts to 450-500 ft.-lbs. using the same criss-cross sequence.
Tightening the nuts as you rotate the wheel on the axle may ensure that you don't miss tightening a nut, but it also will ensure you have a cocked wheel that will run loose.
Most of the teams in the commercial tire service league use 1-inch impact wrenches to tighten lug nuts. These tools have working torque ranges around 100-1,000 ft.-lbs. and maximum torque ranges of about 1,400 to 1,600 ft.-lbs. These really are large ranges, and only incredibly good luck will ensure you achieve the correct 450-500 ft.-lbs. every time.
It is recommended that you let the wrench impact 3-5 seconds to reach the desired 450-500 ft.-lbs. However, if the impact wrench is left on the nut too long, you easily can attain the maximum torque it puts out—like 1,500 ft.-lbs.—which is certain to cause yielded studs, and probably a few broken ones as well.
Both undertorquing and overtorquing wheel nuts can lead to loosened wheels. The only way you can possibly know you have tightened the nuts to the proper torque is to use a torque wrench.
Impact wrenches do a fast job of tightening wheel nuts, but they are not able to determine the actual amount of torque applied. That is why, after wheel assemblies are installed on a vehicle, they should always be checked with a torque wrench to ensure the proper torque level has been achieved. Do this and you'll hit a grand slam every game!