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result in a loss of air pressure. Pumping
the brakes on a long downhill grade may
mean that you do not have enough air
pressure for the brakes to work properly.
• Avoid using the brakes too much going
down hills. Downshift before going
over the top of the hill. Use engine
compression as a way to control your
speed on steep grades.
• If there is a low air pressure warning,
stop as soon as possible in a safe
place. Increase the air pressure before
continuing.
• Before going down a hill, test the brakes.
Look at the air pressure gauge, apply
the brakes, and check for abnormal air
pressure loss. Do not proceed if there is
abnormal pressure loss.
• If the trailer hand valve is used too
much, particularly on steep hills, the
trailer brakes may fail. Use of the trailer
hand valve only is not recommended
as it leads to a greater wear on the
trailer brakes then the truck-tractor
brakes. This causes unbalanced braking
between the truck-tractor and the trailer
which could cause the unit to jackknife.
• Always be sure the brakes are adjusted
properly. If they are not, some brakes
will have to work harder than the others.
This could cause a skid.
• A driver must not pull any trailer that
weighs more than 2,300 kg that is not
equipped with brakes controlled by
the driver.

Coupling and
uncoupling a truck-tractor
and semi-trailer

Coupling

The basic steps for coupling a truck-tractor
to a semi-trailer are as follows:

Chock the semi-trailer wheel. If you only
have one chock, place it to the rear of
the semi-trailer wheel. If you have two
chocks, place one to the front and one
to rear of the semi-trailer wheel.
Check that the jaws on the fifth wheel
are in the unlocked (open) position.
Check the condition of the semitrailer
apron, king pin and it’s collar for
excessive wear or cracks.
Back the truck-tractor in line for the
hook-up with the semi-trailer. Stop
before contact is made between the fifth
wheel and the trailer apron.
Check that the height of the fifth wheel
and the semi-trailer match.

NOTE: Some older trailers may not have
spring brakes.

If the semi-trailer does have spring
brakes on at least one axle, connect air
lines from the truck-tractor to the semitrailer
and fill the trailer air tanks.
Set the semi-trailer brakes.
Back the truck-tractor until a connection
has been made.
Perform a firm tug test to ensure you
have a good hook-up. If noticeable
slack is present, make
necessary corrections.
Visually check that the fifth wheel jaws
are properly locked around the trailer
king pin.
Raise the landing gear and hook-up
the electrical line.
Remove wheel chocks.

CHAPTER FOUR OPERATING CLASS 1 VEHICLES 43

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