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
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
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
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.