Chapter #28 -Truck Brake Systems exam questions and answers

Where should grease be applied on an S-cam brake system components? cam roller pocket race What is the primary function of a relay valve? remote controlled service brake valve Which of the following factors can affect the timing of service brakes? relay valve crack pressures hose and tubing diameters and length replacing a 45-degree fitting with a 90-degree fitting What is the potential energy of an air brake system? compressed air What are S-cam type foundation brakes mounted to? axle spindle Which of the following are function(s) of slack adjusters used on truck air brake systems? Multiply force applied to the S-cams... Define shoe to drum freeplay... Convert linear force to rotational force... When a FMVSS-121 compliant tractor-trailer is running down a highway and the driver applies the service brakes, which of the following is true at the time of the brake application? both service application and hold-off circuits are charged with air When a truck has no air pressure in its tanks, which warning devices are activated when the ignition key is turned on? a buzzer red light a dash gauge When should you cage a spring brake chambers? ~Before attempting to remove and replace it.. ~When making a brake adjustment... ~Before chocking the wheels for service work... If you have to make an adjustment to air system cut-out pressure, where should the adjustment be made? governor In an S-cam foundation brake, where would you find brake shoe rollers? riding the S-cam profiles How many anchor pins are used for a pair of S-cam actuated brake shoes? two 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 An air brake equipped highway tractor features single dash air pressure gauge with two needles, one green and the other red. What does the red needle display? secondary circuit pressure Which of the following terms is often used to describe a truck safety pressure relief valve? pop-off valve Which of the following best describes the functions of a tractor protection valve (TP)? ~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... Which of the following pressure values are FMVSS-121 compliant for governor cut-out and cut-in pressures? cut-out at 125 psi and cut-in at 100 psi How is the relay (secondary) section of an FMVSS-121 compliant dual-circuit foot valve actuated when the air brake circuit is functioning properly? pneumatically