NHTSA Preliminary Evaluation PE08069

ODI opened this investigation based on a review of Early Warning Field reports which indicated instances of the air compressor discharge line coming loose or separating on certain model year 2008 Mack Trucks.Further review indicated that Mack had issued a Service bulletin (#SB 531014) in May 2008.A revised air line was incorporated into production in May 2008 and the ferrule type fitting was changed to a 37 degree flare compression type fitting.The failure resulted in a diminished air supply to the truck's braking system.During the investigation, ODI collected information from Mack, examined warranty claims, discussed the problem with fleet managers and confirmed that the subject vehicles meet the requirements of FMVSS 121, (Air Brake Systems).This standard includes a requirement for an air pressure gauge, and an audible and visual warning signal. The air system normally operates at 100 -120 psi.If the air discharge line becomes loose, the system will continue to hold air but replenishment may be diminished depending on the degree of leakage.If the air line separates, air system replenishment will cease and air pressure will drop as system air is used during brake applications.As the air pressure drops, the dashboard mounted gauge provides a continuous pressure status. Drivers are required to have a CDL (commercial drivers' license) with air brake endorsement and part of the training to obtain such a license includes learning how to monitor and respond to the air pressure system gauges.As the pressure drops below 60 psi, the audible/ visual warning device activates alerting the driver to take appropriate action to stop the truck in a safe location.If the air pressure is allowed to drop below 45 psi, the parking brakes will began to apply.ODI confirmed that approximately 94% percent of the trucks have engine brakes that provide supplemental braking and allow a driver with a leaking discharge line to use the compression of his engine to slow the truck, thus further pr