Maintenance Q&A – November 2020
Fender benders and collision-avoidance systems
Q. You keep referring to the Technology and Maintenance Council as your authority for what to do for maintenance. What makes it such an authority as opposed to anyone else?
A. A short while ago I explained the difference between a TMC recommended practice and a what-to-do manual like Motor or Mitchell 1. TMC recommended practices go into the “why” as well as the “what” of maintenance. Those practices have stood the test of time.
Sixty-four years ago, a group of maintenance managers got together because they were not getting good information from original equipment manufacturers and suppliers. They formed a committee to identify common problems and develop common practices to solve those real-world problems. That committee evolved over time to become a major force in standardizing truck maintenance practices. It also has expanded to include technician development and the anticipation of future maintenance problems based on developments in engineering. In 1985, TMC was recognized by the Society of Automotive Engineers as the technical society speaking for the truck user when TMC presented its first future truck proposals at the SAE annual truck and bus meeting. I was one of the volunteers on that project.
TMC recommended practices are considered what is state of the art in truck maintenance.
They do not have the force of government regulations, but as published documents they can be used to establish legal liability.
Q. I have a 2019 Volvo with all the latest safety devices. I was in a minor fender bender – literally – and parts of my fiberglass fender and bumper got damaged. They were easily repaired but now my collision avoidance system isn’t working. The body shop says they didn’t touch any electronics and there was no damage to their mounting. Can you tell us what’s wrong?
A. When sighting a rifle, a small fraction of a millimeter off at the sight can make your shot miss by feet at the target.
With electronics, even a slight jarring where the sensor is mounted can affect its aim and its performance on the road.
This is not uncommon with many of the electronics in today’s trucks, as was brought up as a common problem at the recent virtual TMC meeting that I attended. Even the most minor impact should be checked by a factory dealer who has the proper electronic equipment to measure and recalibrate any frame- and bumper-mounted electronic safety devices.
Q. A few attendees at TMC brought up the increasing number of wheel-end fires that they have experienced. The acronym used by the government is WETE for “wheel-end thermal events.”
A. A number of possible causes that have been discovered by TMC members, most of which involve brake drag. Even the slightest dragging of brakes can result in wheels heating up to the point that hydrocarbon lubricants and tires can ignite.
Damage to brake lines or chambers: Damage does not have to be catastrophic to cause brake chambers to leak air. Even small air leaks caused by corrosion or being hit by debris can result in springs not being fully withdrawn. This can lead to constant brake drag. With today’s high horsepower, high torque engines, a driver may not become aware of drag on brakes until there is a full-fledged fire visible in the mirrors.
Leaking wheel-end seals: Under some braking conditions drums may heat to more than 600 degrees F. That’s well above the ignition point of hydrocarbon lubricants, both oils and greases.
Out-of-adjustment bearings: Wheel-end bearings must be properly set using dial indicators and setting tools dedicated for that particular bearing. If not properly aligned by pre-load or end-play, friction will build and ignite any leaking fluids.
All these were mentioned at the TMC’s Shop Talk session. The common thread is that wheel-ends and brake chambers have become regular inspection and maintenance items during preventative maintenances.
Q. What other items were brought up as major concerns at TMC?
A. A major ongoing concern is corrosion control and prevention. TMC has formed a study group to work on this. Their recommendations are included in a publication “Corrosion: Complete, Cause and Correction Manual,” one of a number of useful TMC publications.
TMC also looks to the future to anticipate problems before they occur.
For example, electric power is increasing in popularity. It started with medium duty trucks, and today both start-ups and established OEMs are field testing Class 8 prototypes. Voltages in these vehicles vary from 48-volt DC and three-phase AC to as high as 600 volts for hybrid and battery electric vehicles.
One benefit of high-voltage systems is that small-gauge wire can be used throughout the vehicle. Power is measured in watts and calculated as volts times amps. The higher the voltage, the fewer the amps needed for a given watt requirement. A wire’s ability to carry current without overheating is dependent on amps alone. At higher-voltage, smaller-gauge and therefore lighter weight and more flexible wire can be used. Because of the variety of systems being considered, TMC is working with other industry technical groups to color code wiring according to system voltage, thus warning technicians about the systems they are working on. Currently, positive 12-volt wiring is red and 24-volt positive is yellow. Proposals are that 48-volt wiring will be blue, and 60-volt DC and three-phase AC will be orange, as will all higher voltages. Grounds for higher-voltage systems will be white with colored stripes. TMC also is working on personal protective equipment to be used when working on high-voltage systems.
By the time you’re ready for an electric truck – or rather when one is ready for you – TMC will have helped develop the maintenance and repair information you’ll need. LL
For more information on TMC, and to obtain any publications including the Recommended Practices Manual call 703-838-1763. There is a special discounted owner-operator membership available that includes a free copy of the Recommended Practices Manual.