Heavy Duty Trucking

November, 1999

Wheel Service Bible

This guide is required reading for technicians handling tires, wheels.

The Maintenance Council (TMC) of the American Trucking Assns. has the definitive answer on wheel maintenance.  It is published under Recommended Practice 222 and it is a companion to TMC’s tire service guide.  Both deserve a place in any maintenance shop library and should be required reading for any technician who handles tires, wheels or wheelends.

The wheel service guide was generated by wheelend suppliers and is a distillation of the wisdom found in their manuals, combined with the best practices in the industry.  Such is the value of the TMC publication that most of the modern wheel service literature has been brought in line with RP 222.

Following are a few do’s and don’ts that should always be wheel care guidelines.

1. Fasteners wear out.  The nuts and studs that hold wheels to the hub are designed for heavy-duty application but they do wear.  After they have been fastened and removed a number of times, the threads and seats wear.

2. Fasteners corrode.  For that reason, lubrication must be applied sparingly to the threads.  Wheel manufacture guidelines and RP222 say a couple of drops of machine oil should be applied to the threads of the stud.

• Do not over or under lubricate.  Too much oil, or no oil leads to false torque wrench readings with potential wheels-off incidents.

3. Always use a torque wrench to set the final torque.  Set air tools at less than the specified torque - usually 450 pounds feet.  Final torque every time a wheel is removed by using a torque wrench.

4. Air tools cannot be used to reliably torque lug nuts to the specified tension.  Technicians may be able to get close using air tools, but for reliability as well as good shop practice final torquing should be with a torque wrench.

Contamination of the fasteners can give false torque readings.  Threads must be lubricated otherwise the torque reading will be low.  Also, studs will not have sufficient clamping force to retain the wheel.  Keep oil off the ball seats, though, otherwise too much torque will stretch the studs and the clamping force will diminish in use.

If a truck comes in with a broken wheel stud, replace it -- obviously -- and the studs either side of the broken one.  If two or more studs are broken, replace all studs on that hub.

Overloading axles -- and thus overloading studs -- is the main cause of broken studs, which in turn can lead to wheel loss incidents.

Bear in mind that lost wheels is an all-too-common problem that can have lethal repercussions.

When installing wheels, ensure valve stems are 180 degrees separated to make balance and air pressure checking simple.  When torquing, use the proper sequence: hand-tighten first on the studs; impact wrench next starting at the 12 o’clock position then 6 o’clock, then 9 o’clock and so on.  Finally torque the wheel 450 to 500 ft lb.

Use proper tire practices, with mats on the floor to protect the wheels.  A good maintenance practice is to call for 30-day inspections on all wheel equipment with a retorque or the wheel ends registered in a log.