Heavy Duty Truck Systems - Chapter 31 exam questions and answers

Which of the following is the best practice when instructed to block the wheels on a tractor/trailer combination? Place a pair of wedged wheel chocks on one tractor drive axle and one trailer axle wheel. What is the required amount of slack adjuster free travel on a properly adjusted, manual S-cam brake? 3/8 to 5/8 inch Which of the following foundation brake components are lubricated with chassis grease, either for component life or as part of a lube job? S-cam bushings A 161/2 inch brake drum specified to have a machine limit of 0.090 inch over and a maximum dimension of 0.120 inch over is measured at 0.098 inch over at a brake overhaul. Technician A says that the drum can be turned on a drum lathe, providing that the maximum dimension of 0.120 inch is observed. Technician B says that the drum can be legally returned to service without being turned. Who is correct? Technician B only A tandem axle trailer equipped with S-cam brakes has all four slack adjusters originally set with a 6-inch dimension from the clevis pin to the camshaft. One slack adjuster is replaced, and because of a different hole arrangement in the new slack adjuster, it is set at 61/2 inches. Which of the following is more likely to result? One of the four wheels will lock up ahead of the others under severe braking When adjusting a manual slack adjuster on an S-cam foundation brake, Technician A says that the lock collar should be retracted and the adjusting nut always rotated clockwise to decrease free travel. Technician B says that free travel can be reduced only when the adjusting nut is rotated counterclockwise. Who is correct? Neither A nor B A set of brake linings has become glazed because of oil saturation by a failed wheel seal. Technician A says that pressure washing the foundation brake components should be sufficient to remove the effects of the oil saturation. Technician B says that the best practice is to replace the brake linings on both wheels on the affected axle. Who is correct? Technician B only When adjusting S-cam brakes on a trailer equipped with manual slack adjusters, which of the following must be true? The trailer parking brakes must be released An original equipment 45-degree elbow on a line exiting a relay valve supplying a service chamber is replaced by a 90-degree elbow. Technician A says that this should have no effect on brake performance because it is the service application pressure that determines braking force. Technician B says that the use of the 90-degree elbow increases flow restriction and can affect pneumatic timing. Who is correct? Technician B only