WARNING

Keep legs and feet clear of the rear of the tractor wheels to avoid injury should the tractor move.

Step 6. Pull tractor partially clear of trailer

Pull tractor forward until the fifth wheel comes out from under the trailer.

Stop with the tractor frame underneath the trailer. This prevents the trailer from falling to the ground if the landing gear should collapse or sink.

Step 7. Secure tractor

Apply the parking brake.

Disengage the trailer hand valve to release trailer brakes.

Place the manual transmission in neutral; in park, if an automatic transmission.

Figure 7-19.-Air line storage dummy couplers.

Step 8. Secure trailer

l 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).

l Ensure the lines are supported so they will not be damaged while driving the tractor.

l Ensure the ground is supporting the trailer.

l 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.

Accelerating

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 accelerator pedal.

Steering

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.

Shifting Gears

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 components.

Most tractor-trailers with manual transmissions require double clutching to change gears. The procedures 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 correct gear.

You can use two factors to tell when to shift the transmission. One is the engine rpm. The operator's 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 operator's manual before operating a tractor with an unfamiliar transmission shifting pattern.

Figure 7-20.-Right turn.

AUTOMATIC TRANSMISSIONS.- Some tractors in the NCF are equipped with automatic transmissions. A low range can be selected to have a greater engine braking power when going down grades. The lower ranges prevent the transmission from shifting up beyond the selected gears. Shifting an automatic transmission incorrectly can cause serious damage to the transmission; therefore, operators must study the operator's manual for techniques of shifting automatic transmission.