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NOTE: Information in this section is not all inclusive and is subject to change due to law changes. For the latest information refer to the current CDL Manual for the
state you live in.
Please be sure to read the pre trip inspection section that applies to all commercial motor vehicles.
Additional Pre Trip Inspection Information for Double/Triple Trailers

Coupling System Areas (Pre Trip Inspection)
  • Check the fifth wheel (lower).
  • Securely mounted to the frame.
  • No missing or damaged parts.
  • Enough grease.
  • No visible space between the upper and lower fifth wheel.
  • Locking jaws are around the shank, not the head of kingpin.
  • Release arm is properly seated and the safety latch/lock is engaged.
  • Fifth wheel (upper).
  • Apron is securely mounted to the trailer frame, not bent, cracked or broken.
  • Kingpin is not damaged.
  • Air and electric lines to the trailer.
  • Electrical cord is firmly plugged in and is secured.
  • Air lines are properly connected to the glad hands, there are no air leaks, they are properly secured with enough slack for turns.
  • All lines are free from damage.
  • Sliding fifth wheel.
  • Slide is not damaged or there are no parts missing.
  • Properly greased.
  • All locking pins are present and are locked in place.
  • If air powered, there are no air leaks.
  • Check that fifth wheel is not so far forward the tractor frame will hit the landing gear, or the cab will hit the trailer during turns.

Landing Gear (Pre Trip Inspection)
  • Fully raised, there are no missing parts, it is not bent or otherwise damaged.
  • Crank handle is in place and is secured.
  • If power operated, there are no air or hydraulic leaks.

Double and Triple Trailers (Pre Trip Inspection)
  • Shut-off valves (at the rear of trailers, in the service and emergency lines):
  • Rear of front trailers: OPEN.
  • Rear of last trailer: CLOSED.
  • Converter dolly air tank drain valve: CLOSED.
  • Be sure the air lines are supported and the glad hands are properly connected.
  • If the spare tire is carried on the converter gear (dolly), make sure it is secured.
  • Be sure the pintle-eye of the dolly is in place in the pintle hook of the trailer(s).
  • Make sure the pintle hook is latched.
  • Safety chains should be secured to the trailer(s).
  • Be sure light cords are firmly in the sockets on trailers.


Use the tractor parking brake and/or chock the wheels to hold the vehicle. Wait for air pressure to reach normal, then push in the red “trailer air supply” knob. This will
supply air to the emergency (supply) lines. Use the trailer handbrake to provide air to the service line. Go to the rear of the rig. Open the emergency line shut-off valve
at the rear of the last trailer. You should hear air escaping, showing the entire system is charged. Close the emergency line valve. Open the service line valve to
check that service pressure goes through all the trailers (this test assumes that the trailer handbrake or the service brake pedal is on), then close the valve. If you do
NOT hear air escaping from both lines, check that the shut-off valves on the trailer(s) and dolly(s) are in the OPEN position. You MUST have air all the way to the back
for all the brakes to work.

Charge the trailer air brake system. (That is, build up normal air pressure and push the “air supply” knob in.) Shut the engine off. Step on and off the brake pedal
several times to reduce the air pressure in the tanks. The trailer air supply control (also called the tractor protection valve control) should pop out (or go from the
“normal” to “emergency” position) when the air pressure falls into the pressure range specified by the manufacturer, usually within the range of 20 to 45 psi. If the
tractor protection valve does not work right, an air hose or trailer brake leak could drain all the air from the tractor. This would cause the emergency brakes to come
on, with possible loss of control.

Charge the trailer air brake system and check that the trailer rolls freely. Then stop and pull out the trailer air supply control (also called tractor protection valve control
or trailer emergency valve) or place it in the “emergency” position. Pull gently on the trailer with the tractor to check that the trailer emergency brakes are on.

Check for normal air pressure, release the parking brakes, move the vehicle forward slowly, and apply trailer brakes with the hand control (trolley valve), if so
equipped. You should feel the brakes come on. This tells you the trailer brakes are connected and working. The trailer brakes should be tested with the hand valve,
but controlled in normal operation with the foot pedal, which applies air to the service brakes at all wheels.
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Commercial Drivers License (CDL) Pre-Trip Inspection: Double/Triple Trailers
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