Commercial Driver License Study Group

2012

Combination Vehicles

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

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

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

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

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

Combination air brakes

• Trailer hand valve - only to test trailer brakes

• Tractor protection valve

• Trailer air supply control

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

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

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

Anti-lock brakes

• After 1998 – ABS required

• Yellow ABS malfunction lamps

• Early models – hard to tell

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

Coupling & Uncoupling

• Coupling – 16 steps

• Uncoupling – 10 steps

Inspecting a combination

• New items to inspect

– Fifth wheel (lower)

– Fifth wheel (upper)

– Air and electric lines to trailer

– Sliding fifth wheel

– Landing gear

Combination brake check

• Air flows to all trailers

• Test Tractor Protection Valve

• Test Trailer Emergency Brakes

• Test Trailer Service Brakes