commercial driver lincense - part 6
TRANSCRIPT
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Commercial Driver License Study Group
2012
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Combination Vehicles
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Driving safely
• Rollover risks – Keep cargo low and centered
– Drive slowly around curves
• Steer gently – Rearward amplification = crack the whip effect
– Steer gently & smoothly
– Following distance is longer
– Look ahead
– Slow down at night
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Driving safely
• Brake early
– Take longer to stop when empty than fully loaded
– Bobtail tractors
• Railroad-highway crossings
– Low slung units
– Long trailer….
– Get out of vehicle and away from tracks
– Call 911
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Driving safely
• Skids are more likely when trailer is empty or lightly loaded
– Use mirror to check trailer
– Release brakes to get traction back
• Turn wide
– Offtracking or cheating
– Rear wheels of last unit will offtrack the most
– Keep rear wheels near curb
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Driving safely
• Backing a trailer – Turn steer wheel in the opposite direction of where
you want to go
– Once the trailer starts to turn, you must turn the wheel the other way to follow the trailer
– Position vehicle to back in a straight line
– If curved, back to the driver’s side so you can see
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Driving safely
• Get out and look at path
• Check outside mirrors
• Back slowly
• Correct drift by turning steering wheel in direction of drift
• Pull up to reposition vehicle as needed
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Combination air brakes
• Trailer hand valve - only to test trailer brakes
• Tractor protection valve
• Trailer air supply control
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Combination air brakes
• Service air line
– Air controlled by foot brake pedal
• Emergency air line
– Air to trailer air tanks
– Loss of air pressure causes trailer emergency brakes to come on and tractor protection valve to close
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Combination air brakes
• Hose couplers (Glad Hands)
– Connect service and emergency air lines from truck or tractor to the trailer
– Color coded red, blue
– Test brakes before driving
– Keep clean – dummy couplers
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Combination air brakes
• Trailer air tanks
– Drain each tank every day
• Shut-off valves
– Between or at end of trailers
• Trailer service, parking & emergency brakes
– After 1975 = spring brakes
– Earlier = air brakes + chocks
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Anti-lock brakes
• After 1998 – ABS required
• Yellow ABS malfunction lamps
• Early models – hard to tell
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Braking with ABS
• Does not change normal braking
• Activates when wheels are about to lock up
• Helps keep vehicle under control by reducing braking pressure to a safe level
• Use only force necessary
• Brake same way
• As slow down, monitor, back off brakes
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Coupling & Uncoupling
• Coupling – 16 steps
• Uncoupling – 10 steps
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Inspecting a combination
• New items to inspect
– Fifth wheel (lower)
– Fifth wheel (upper)
– Air and electric lines to trailer
– Sliding fifth wheel
– Landing gear
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Combination brake check
• Air flows to all trailers
• Test Tractor Protection Valve
• Test Trailer Emergency Brakes
• Test Trailer Service Brakes