Figure 7-19.Air line storage dummy couplers.
Step 8. Secure trailer
Disconnect the air lines from the trailer. Connect
the air line glad hands to dummy couplers at the
back of the tractor cab (fig. 7-19).
Ensure the lines are supported so they will not
be damaged while driving the tractor.
Ensure the ground is supporting the trailer.
Ensure the landing gear is not damaged.
Step 9. Pull the tractor clear of trailer
l Release the parking brakes.
. Check the surrounding area and drive the tractor
clear of the trailer.
When driving a tractor-trailer, you must not roll
backward when you start, because you may hit a vehicle
behind you. Partly engage the clutch before taking your
right foot off the brake. If on an incline, engage the
parking brake to hold the tractor, then release the
parking brake only when you have applied enough
engine rpm to keep from rolling backward. Another
technique is to engage the engine hand throttle to
increase the engine rpm while your right foot is on the
brake and your left foot is partly engaging the clutch. As
the clutch engages, release the foot brake, and disengage
the engine hand throttle.
Accelerate smoothly and gradually so the tractor
does not jerk. Rough acceleration causes unnecessary
premature mechanical damage to the drive train and to
the coupling. When traction is poor as in rain or snow,
speed up gradually. Using too much power may cause
the drive wheel to spin. If the drive wheels lose traction,
do not apply the brakes; just take your foot off the
When steering, hold the steering wheel firmly with
both hands on the opposite sides of the wheel. Should
you hit a pothole or a curb, the steering wheel could pull
away from your hands if you do not have a firm hold.
Correct shifting of gears is important. Not only must
you have full control of your tractor-trailer, but
grinding to find them, a term used when a driver
forces the gears to engage, clutch slipping, rapid
engagement during shifting, improper downshifting,
and so forth, causes premature failure of drive-line
Most tractor-trailers with manual transmissions
require double clutching to change gears. The pro-
cedures for double clutching were covered in chapter 2.
Remember: Shifting gears using double clutching
requires practice. If you remain too long in neutral, you
may have difficulty putting the transmission into the
next gear. If this happens, do not try to force it. Instead,
return to neutral, release the clutch, increase engine
speed to match the road speed, and try to shift into the
You can use two factors to tell when to shift the
transmission. One is the engine rpm. The operators
manual tells you the operating rpm range for the tractor.
Using the tachometer, shift up when the engine reaches
the top of the range. The second factor is the road speed
(mph). Through experience you will learn what speeds
each gear is good for. Then by using the speedometer or
engine sound, you will know when to shift.
MULTI-SPEED REAR AXLES AND AUXIL-
IARY TRANSMISSIONS. Multi-speed rear axles
and auxiliary transmissions are used on many tractors
to provide extra gears. These gears are shifted by a
selector knob or switch on the gearshift lever of the main
transmission. Many different transmission shifting
patterns are used; therefore, it is important that the
operator study the operators manual before operating a
tractor with an unfamiliar transmission shifting pattern.