1/8 inch (3 mm), adjust the jaw to restore the
1/16-inch (1.6-mm) clearance between the jaw
and kingpin. For instructions, see Group 31 of
the
Century Class Trucks Workshop Manual
.
12. Retract the trailer landing gear, and secure the
ratchet handle.
13. Remove the chocks from the trailer tires.
14. The load distribution on the front steering axle
and rear drive axle(s) will have a direct effect on
the steering control of the vehicle.
Determine the front and rear axle weights by
weighing the vehicle on scales designed for this
purpose.
The maximum axle weight ratings are shown on
the Federal Motor Vehicle Safety Standard
(FMVSS) label or Canadian Motor Vehicle Safety
Standard (CMVSS) label attached to the left rear
door post of the tractor. The desired load on the
axle is no less than 80 percent of the maximum
axle weight rating, but in no instances should the
axle load exceed the maximum axle weight rat-
ings given on the FMVSS or CMVSS label.
WARNING
Do not overload any tractor axle by improperly
loading the trailer. This could cause erratic steer-
ing and loss of vehicle control, possibly resulting
in serious personal injury or death.
Unlocking the Fifth Wheel Lock
Mechanism
1.
Apply the tractor parking brakes.
2.
Pull the trailer air supply valve to cut off the air
supply to the trailer.
WARNING
Do not use the trailer air supply for parking trail-
ers not equipped with spring parking brakes.
This applies the trailer service brakes only. As air
bleeds from the trailer brake system, brake appli-
cation is lost. This could allow the unattended
vehicle to roll away, possibly resulting in serious
personal injury or death.
3.
Chock the front and rear of the trailer tires to
prevent the trailer from moving.
4.
Lower the trailer landing gear until the trailer
rises about 1/2 inch (13 mm).
5.
Disconnect the tractor-to-trailer air system lines
and electrical cable. Plug the air lines to prevent
dirt or foreign material from entering the lines.
NOTICE
Before attempting to unlock the fifth wheel lock
mechanism of a sliding type fifth wheel, the slide
operating rod (
Fig. 10.9
) must be in the locked
position, and the slide lockpins must be in the
locked position (fully inserted in baseplate rail
slots). This prevents the sliding member from
moving rapidly to the far forward or rearward po-
sition, which could damage the fifth wheel mem-
ber or kingpin.
6.
If equipped with a manual kingpin lock release:
Release the kingpin lock mechanism by raising
the safety latch to the rear and pulling the lock
operating rod out and up into the lockset posi-
tion. See
Fig. 10.11
. The offset of the lock con-
trol upper rod should bottom against the plate
casting above the hole. If the operating rod can-
not be pulled to the lockset position, back the
tractor slightly to release the kingpin force
against the jaw.
If equipped with an air-operated kingpin lock re-
lease:
Pull the air-release knob on the dash.
From outside the cab,
visually check that the op-
erating rod has bottomed out against the plate
casting above the hole. See
Fig. 10.11
. If the
operating rod isn’t in the unlocked position, back
the tractor slightly to release the kingpin force
against the jaw.
IMPORTANT: If equipped with an air-operated
lock release, you still must make a visual check
of the operating rod to make sure it is in the un-
locked position
7.
Slowly drive the tractor away from the trailer.
Fifth Wheel Slide Operation
1.
Chock the front and rear of the trailer tires to
prevent the trailer from moving.
2.
Connect the trailer kingpin to the tractor fifth
wheel. For instructions, refer to "Fifth Wheel
Locking Operation," in this chapter.
Fifth Wheels and Trailer Couplings
10.9