Commercial Driver License Study Group

2012

Section 7 Doubles and Triples

Driving safely

• Steer gently

• Drive slowly on curves, on/off ramps, corners

• Last trailer most likely to turn over

• More critical parts to inspect

Driving safely

• Look far ahead

• More space needed – front/back/sides

• More careful in adverse condition

• Park to pull straight through

• Converter dollies have anti-lock brakes

Coupling / uncoupling

• For safest handling on road, put heaviest trailer immediately behind tractor, then lighter trailer

• Converter gear on a dolly is a coupling device of 1 or 2 axles and a fifth wheel by which a semitrailer can be coupled to the rear of a tractor-trailer combination forming a double bottom rig.

Coupling / Uncoupling Twin Trailers

• Sequence on pages 7.1 to 7.2

Coupling / Uncoupling Triple Trailers

• Sequence page 7.2

Inspecting Doubles & Triples

• Coupling system areas

– Fifth wheel (lower)

– Fifth wheel (upper)

– Air and electric lines to trailer

– Sliding fifty wheel

Inspecting Doubles & Triples

• Landing gear

– Fully raised, no missing parts, not damaged

– Crank handle in place and secured

– If power operated, no air or hydraulic leaks

Inspecting Doubles & Triples

• Double & triple trailers

– Shuf-off valves

– Air lines supported and glad hands connected

– Spare tire secure

– Pintle-eye of dolly in place

– Pintle hook latched

– Safety chains secured to trailers

– Light cords are firmly in sockets on trailers

Air brake check

• Check as for any combination vehicle plus ---

• Air flows to all trailers

– Put on tractor parking brake

– When air pressure up, push in “trailer air supply” knob = supply air to emergency lines.

– Use trailer handbrake to put on trailer service brakes

Air brake check

• At back of last trailer

– Open emergency line shut-off valve = hear air

– Close it

– Open the service line valve = hear air

– Close it

– If you do NOT hear air escaping, check valves up the line – they should be OPEN.

Air brake check

• Test tractor protection valve

– Build up normal air pressure and push “air supply” knob in

– Shut engine off

– Step on/off brake pedal to reduce air pressure

– Tractor protection valve should pop out at 20 to 45 psi

– Failure to do so = emergency brakes come on

Air brake check

• Test trailer emergency brakes

– Charge trailer air brake system

– Trailer rolls freely

– Stop, pull out trailer air supply control

– Pull gently on trailer with tractor

Air brake check

• Test trailer service brakes

– Check for normal air pressure

– Release parking brakes

– Move vehicle forward slowly

– Apply trailer brakes (with hand control – trolley valve)

– Should feel brakes come on

– NOTE: tested with hand control, drive with foot pedal