Figure  7-19.—Air  line  storage  dummy  couplers. Step 8. Secure trailer l l l 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). 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. 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 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 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. 7-18