CDL combination vehicles practice test 3

D: A single-axle tractor pulling a long trailer with its landing gear set for a tandem-axle tractor. The manual lists a single-axle tractor pulling a long trailer whose landing gear is set for a tandem-axle tractor. Commercial Driver's License Manual (CDL Driver's Manual): 6.1.4 Railroad-highway Crossings, page 6-2.

A: 20 to 45 psi. When pressure falls into the 20 to 45 psi range, the tractor protection valve closes on its own. 49 CFR 393.43(a) also requires it to operate automatically between 20 and 45 psi. Commercial Driver's License Manual (CDL Driver's Manual): 6.2.2 Tractor Protection Valve, page 6-5.

C: The outside mirrors on both sides, checked frequently. Check the outside mirrors on both sides frequently, and get out and re-inspect your path if you are unsure. Commercial Driver's License Manual (CDL Driver's Manual): 6.1.7 Backing with a Trailer, page 6-4.

D: It may catch on railroad tracks or other things. Never drive with the landing gear only part way up, because it may catch on railroad tracks or other things. Commercial Driver's License Manual (CDL Driver's Manual): 6.4.1 Coupling Tractor-Semitrailers, page 6-9.

B: Air is let out of the trailer emergency line, so the trailer emergency brakes come on. When it closes, the tractor protection valve stops air from leaving the tractor and lets air out of the trailer emergency line. The trailer emergency brakes then come on, with possible loss of control. Commercial Driver's License Manual (CDL Driver's Manual): 6.2.2 Tractor Protection Valve, page 6-5.

A: The trolley valve or Johnson bar. The trailer hand valve is also called the trolley valve or Johnson bar, and it works the trailer brakes. Commercial Driver's License Manual (CDL Driver's Manual): 6.2.1 Trailer Hand Valve, page 6-4.

B: It pops out, closing the tractor protection valve. The valve pops out, closing the tractor protection valve, when air pressure drops into the 20 to 45 psi range. Commercial Driver's License Manual (CDL Driver's Manual): 6.2.3 Trailer Air Supply Control, page 6-5.

B: Only to test the trailer brakes. Use the hand valve only to test the trailer brakes. Braking with it while driving can make the trailer skid. Commercial Driver's License Manual (CDL Driver's Manual): 6.2.1 Trailer Hand Valve, page 6-4.

C: The loss of pressure in the emergency line makes the trailer emergency brakes come on. When the emergency line loses pressure, the trailer emergency brakes apply. The tractor protection valve also closes, so the air supply knob pops out. Commercial Driver's License Manual (CDL Driver's Manual): 6.2.4 Trailer Air-lines, page 6-5.

C: The foot brake sends air to all the brakes, so there is much less danger of a skid or jackknife. The foot brake sends air to all the brakes on the vehicle, including the trailers, so there is much less danger of a skid or jackknife than with the hand valve. Commercial Driver's License Manual (CDL Driver's Manual): 6.2.1 Trailer Hand Valve, page 6-4.

C: You could drive away with no trailer brakes. Older trailers have no spring brakes. If the lines are crossed, the rig can still move but the trailer has no brakes at all, which is very dangerous. Commercial Driver's License Manual (CDL Driver's Manual): 6.2.5 Hose Couplers (Glad Hands), page 6-6.

A: The trailer air supply control valve. The driver opens and closes the tractor protection valve with the trailer air supply control in the cab. Commercial Driver's License Manual (CDL Driver's Manual): 6.2.2 Tractor Protection Valve, page 6-5.

C: When you try to put on the brakes. You may not notice a major service line leak until you brake. The leak then lowers tank pressure quickly, and if it gets low enough the trailer emergency brakes come on. Commercial Driver's License Manual (CDL Driver's Manual): 6.2.8 Trailer Service, Parking and Emergency Brakes, page 6-6.

B: A red eight-sided knob. On newer vehicles the trailer air supply control is a red, eight-sided knob. The yellow diamond knob is the parking brake. Commercial Driver's License Manual (CDL Driver's Manual): 6.2.3 Trailer Air Supply Control, page 6-5.

C: The kingpin may be on top of the closed fifth wheel jaws, and the trailer could come loose very easily. Space between the upper and lower fifth wheel means something is wrong: the kingpin may be sitting on top of the closed jaws, and the trailer would come loose very easily. Commercial Driver's License Manual (CDL Driver's Manual): 6.4.1 Coupling Tractor-Semitrailers, page 6-8.

C: The air to the trailer is shut off and the trailer emergency brakes come on. Pushing the red knob in sends air to the trailer. Pulling it out cuts off the trailer's air and sets the trailer emergency brakes. Commercial Driver's License Manual (CDL Driver's Manual): 6.2.3 Trailer Air Supply Control, page 6-5.

D: An air hose or trailer brake leak could drain all the air from the tractor, setting the emergency brakes with possible loss of control. A faulty tractor protection valve could let a trailer hose or brake leak empty the tractor's air. That would set the emergency brakes and could cause loss of control. Commercial Driver's License Manual (CDL Driver's Manual): 6.5.2 Combination Vehicle Brake Check, page 6-14.

B: Normal. On older lever-type controls you pull a trailer with the lever in 'normal'. 'Emergency' cuts off the air and sets the trailer emergency brakes. Commercial Driver's License Manual (CDL Driver's Manual): 6.2.3 Trailer Air Supply Control, page 6-5.

B: They may not operate automatically, and may be a lever rather than a knob. On older vehicles the tractor protection (emergency) valve control may be a lever instead of a knob, and it may not work automatically. Commercial Driver's License Manual (CDL Driver's Manual): 6.2.3 Trailer Air Supply Control, page 6-5.

C: The service line and the emergency line. Each combination vehicle has a service line and an emergency line connecting every unit: tractor to trailer, trailer to dolly, and so on. Commercial Driver's License Manual (CDL Driver's Manual): 6.2.4 Trailer Air-lines, page 6-5.

C: The control line or signal line. The service line is also called the control line or signal line. It carries air controlled by the foot brake or the trailer hand brake. Commercial Driver's License Manual (CDL Driver's Manual): 6.2.4 Trailer Air-lines, page 6-5.

B: How hard you press the foot brake or the trailer hand valve. Pressure in the service line changes with how hard you press the foot brake or hand valve. Commercial Driver's License Manual (CDL Driver's Manual): 6.2.4 Trailer Air-lines, page 6-5.

A: They let the trailer brakes be applied more quickly than would otherwise be possible. Relay valves on the service line let the trailer brakes come on faster than they otherwise could. Commercial Driver's License Manual (CDL Driver's Manual): 6.2.4 Trailer Air-lines, page 6-5.

A: It supplies air to the trailer air tanks and controls the emergency brakes on combination vehicles. The emergency (supply) line has two jobs: it supplies air to the trailer air tanks, and it controls the emergency brakes on combination vehicles. Commercial Driver's License Manual (CDL Driver's Manual): 6.2.4 Trailer Air-lines, page 6-5.

C: Emergency lines red, service lines blue. Emergency lines are often coded red (red hose, red couplers, or other parts) so they aren't mixed up with the blue service line. Commercial Driver's License Manual (CDL Driver's Manual): 6.2.4 Trailer Air-lines, page 6-5.