Christian P. Koop
In November 2013, I wrote about emergency response vehicle (ERV) fleet defects I have encountered over the years that can repeat themselves even in different makes, models, and equipment vocations.
I began the article with an analogy about how history seems to repeat itself-not only in recorded history but also with trucks, automotive equipment in general, and ERVs in particular. I feel it can be beneficial to others involved in ERV maintenance and repair to communicate these past fleet-wide issues because they can repeat themselves. The driving force behind writing about these cases is sharing past experiences with the hope that it may help someone get a difficult issue resolved and get a unit back into service sooner rather than later. I have witnessed these issues recur time and time again. Being forewarned about these issues will effectively forearm you to help resolve a problem.
In this article, I cover two cases involving a new fleet that had steering system defects and directional control issues because of an improperly wired antilock braking system (ABS) and traction control system.
Steering Miter Boxes
One fleet defect I have seen repeatedly is the steering system miter box and the security and design of how it is mounted to the chassis or cab. The steering miter box is necessary when the location of the steering column in the cab is forward of where the steering gear box is located or mounted on the chassis. Most miter boxes I have seen on fire apparatus are 1:1 ratio, 90-degree types and are used to redirect the steering shaft output from the steering column back toward the power steering gear that is mounted on the chassis, generally somewhere below the driver’s seating position.
I distinctly remember when a critical problem was detected in a group of aerial fire apparatus during a predelivery inspection of a group of new aerial apparatus at the manufacturer’s facility. While I was inspecting the steering system, I noticed the miter box had been mounted on an L-type bracket constructed out of what appeared to be a ⅜-inch aluminum plate that was bent at 90 degrees. What really caught my eye was that it had no gussets or any form of reinforcement. Becoming suspicious of its mounting integrity, I had one of the inspection team members rock the steering wheel back and forth with the engine off while I checked the miter box for movement. Just as I feared, the bracket flexed excessively. We reported the problem to engineering, and the miter box mounting bracket was redesigned with the appropriate welded gussets to ensure it would support the miter without any undue flexing or movement.
This was done prior to accepting and placing the units into service. I think most reading this can imagine what could have happened had those units left the factory with defective miter box mounting brackets. If a miter box bracket had broken during operation, the steering could have locked, causing loss of directional control for the operator. Loss of steering is a scary thought, and just think of the possible legalities involved if someone was seriously injured or killed had there been an accident. A good attorney would have a field day with a failure of this type involving such a safety-sensitive component that should be properly engineered and tested prior to being placed into production.
I must also mention this was not an anomaly because I have seen issues with how this component is mounted not just on fire apparatus but also on other vehicles. A few years after the previous case, I was invited to inspect a new type of refuse truck cab and chassis where I discovered a very similar issue where the miter box flexed excessively because the mounting location was not structurally sound for the torque loads placed on it during steering.
This is an item technicians must check thoroughly when examining the steering system during preventive maintenance inspections. It is most important to ensure the mounting bolts are tight, that there are no cracks in the mounting bracket if it is equipped with one, and that there is no movement or indication of movement during static steering. The gears in the miter boxes also wear out after normal use over the years, and the gear lash must be checked. Refer to the miter box manufacturer’s specifications for exact procedures to test gear lash and wear.
ABS and Traction Control
This next example involves a fleetwide defect involving vehicle directional control. These units were front-wheel-drive pumpers equipped with ABS and traction control. The problem was discovered while road testing during the specification and acceptance inspection phase at the shop level and would only occur when road conditions were either slippery or wet. To complicate matters even more, the loss of control would only occur while turning under moderate to hard acceleration. This problem was duplicated several times, the manufacturer was contacted formally, and the problem was resolved.
To put things into perspective, imagine driving out of a parking lot, making a right-hand turn onto a two-lane road, accelerating, and the truck sliding over the width of one lane so quickly that there was nothing the driver could do to prevent it.
To get a full understanding of what was occurring, I need to give a brief explanation of how a traction control system works. The units were equipped with air brakes that would be activated or pulsed by the ABS electronic control unit (ECU) if one of the front wheels lost traction during acceleration up to a given vehicle speed. The pulsing of the wheel losing traction would continue until it regained traction-information the ABS ECU continuously receives from the wheel speed sensors. If vehicle speed went above the predetermined parameter, the ECU would take over and derate engine rpm for a brief moment to allow the wheel to regain traction. The problem with the affected units was that the wires for the left and right brake ABS actuation valves were crossed in an electrical connecter. Because of this this error, when the unit went into traction control mode, it pulsed the incorrect wheel, causing both front wheels to lose traction. When this occurred, the driver would immediately lose control of the truck, and the unit would slide out of control.
This was a simple mistake that occurred while the wiring harnesses were assembled at the factory. However, it could have resulted in an accident. The key to remember in this example is that a simple yet critical mistake at the factory level can get past factory quality control and end up in your fleet undetected. Luckily, there were no accidents in this case, and everyone involved learned from the experience. Just keep in mind that, unfortunately, history usually repeats itself.
CHRISTIAN P. KOOP is the fleet manager for the Miami-Dade (FL) Fire Department. He has been involved in the repair and maintenance of autos, heavy equipment, and emergency response vehicles for the past 35 years. He has an associate degree from Central Texas College and a bachelor’s degree in public administration from Barry University and has taken course work in basic and digital electronics. He is an ASE-certified master auto/heavy truck technician and master EVT apparatus and ambulance technician. He is a member of the board of directors of EVTCC and FAEVT and a technical committee member for NFPA 1071, Standard for Emergency Vehicle Technician Professional Qualifications.