Heavy truck brakes test exam questions and answers

When a truck has no air pressure in its tanks, which warning devices are activated when the ignition key is turned on? A buzzer, a dash gauge and a red light What legislation mandates every required standard of a highway truck air brake system? FMVSS 121 If a truck is FMVSS 121 compliant, which of the following air reservoirs must be incorporated into the air brake circuit? Supply, primary and secondary tanks In a truck air brake system which sub circuit is primarily responsible for actuating front axle service brakes when the system is functioning normally? Secondary circuit When a FMVSS 121 compliant tractor trailer combination is moving down the highway at a speed of 50 mph, which circuit must be charged with air? Hold off circuit What best describes the functions of a tractor protection valve? Pressure protects the tractor air supply in the event of loss of pressure in a trailer Routes trailer supply air and service application signal to the trailer pneumatic circuits Blocks service signal air to the trailer until trailer air supply is activated If you have yo make an adjustment to air system cut off pressure where should the adjustment be made? The governor How is the relay section of an FMVSS 121 compliant duel circuit foot valve activated when the air brake is functioning properly? Pneumatically What is the function of a quick release gladhand when used? Speeds service brake release timing What best accounts for brake feel in an air brake system? Resistance of application pressure versus for pressure What is the potential energy of an air brake system? Compressed air When a tractor spring brake assembly is charged with air on both its service and hold off chambers what results is known as? Compounding What is true about hold off pressure in current truck and trailer air brake systems? Its regulated at 90 psi. What is the minimum compressed air reservoir volume dedicated to the air brakes required by an FMVSS 121 compliant highway trailer? 8 times total brake chamber volume What term is used to describe a truck safety pressure relief valve? Pop off valve What pressure is a pop off valve set to trip at in most highway truck applications? 150 psi. When an inversion valve is activated, what happens? Some hold off air is exhausted When a properly functioning treadle valve is actuated by foot pressure, which of the following will determine what pressure is metered out to actuate the primary and secondary service circuits? A. Mechanical force is applied to the treadle B. Actual travel of the primary piston C. Actual system pressure at the time of the application D. Mechanical force applied to the relay piston Mechanical force applied to the treadle Technician A says that the relay section of a dual circuit foot valve is actuated mechanically under normal operation. Technician B says that a primary piston of a foot valve is actuated mechanically under normal operation. Who is correct? Tech B Technician A says that a trailer service brake signal is always sourced from the tractor primary circuit. Technician B says that a trailer service signal can only pass through a tractor protection valve when it is in its ON state. Who is correct? Tech B Technician A says that most current highway tractors use a 3-line TP valve. Technician B says that a 2-line TP valve will remain OFF until the trailer air supply dash button is depressed. Who is correct? Tech B How man anchor pins are used for a pair of S-cam actuated brake shoes? Two What term is used to measure the aggressiveness of friction linings? The coefficient of friction