Landscaping Trailer Electric Brake System


R. Scott King, BSME ::::

Case Analysis: Landscaping dump truck and trailer were involved in a collision with a tractor-trailer that was parked on the roadway shoulder.  After the incident, police inspected the landscaping trailer and determined its brakes were “out of adjustment”, thus contributing to the incident.  The ensuing Complaint echoed the findings and conclusions expressed in the police report.  Service records revealed a third-party maintenance company performed minor services to the trailer several months before the incident and, because of this, was joined in the suit.  Their defense counsel retained an engineering expert familiar with trailer brakes to investigate and, if possible, counter the complaint allegations.

Expert Analysis: The investigation and analysis revealed the incident trailer was equipped with electric brakes.  Such a braking system requires an electrical connection between the trailer and the towing vehicle.  The towing vehicle is equipped with a controlling device that provides the trailer brakes an electrical voltage proportional to the force with which the operator applies the brake pedal. Further, because the weight of a trailer’s load is typically variable, the electrical voltage to the trailer’s brakes must also be variable. An adjustable setting, or “gain” control, on the device provides this electrical variation.  Normal operating procedures require an operator to adjust the gain setting on the brake controller to ensure that the trailer brakes are balanced with the brakes on the towing vehicle.  The trailer should not “push” the towing vehicle, indicating the gain is set too low; nor should its brakes lock prematurely, indicting the gain is too high.  Typically, this process is accomplished by trial and error and has nothing to do with vehicle maintenance.  Moreover, subsequent testimony revealed that the police conclusion regarding the improperly adjusted trailer brakes was related to gain setting, not maintenance.

Result: The resulting expert opinions were able to rebut the assertions that the actions or inactions of third-party maintenance provided contributed to the incident and facilitated a settlement.

Categories: Case Studies


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