Newbies - Tips From the Trainer

Automatic Transmissions / Airbrake Airline Colors

By Fozzy

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I was curious, is it true that you can take a skills test in an automatic transmission semi truck and still be able to drive a standard transmission? And, if this is so, how can they score you on how you shift a standard if you don't even have to take the test in one? No offense, but it's my truck. I should be able to tear the transmission up if I so choose as long as I drive the speed limit and stop at the stop signs, right?


There is nothing that says you cannot take the skills test in a truck equipped with an automatic transmission. There are some things that simply become "freebies" on the skills test if the truck is not equipped with a particular item or piece of equipment. It's impossible to test or grade something that is not actually on the truck. A good example would be if the person brings a flat bed trailer to the CDL test. There is no way to actually check the doors, seals and latches. An automatic transmission could be seen by some as "cheating." If the person is actually going into a job where they are driving an automatic, then it's really not an issue. If they are taking the test to simply make it through the test, they are in for a rude awakening when they get to the company's road test and are not hired because they simply cannot drive.

The CDL skills test is mainly about testing drivers' skills in safely operating the vehicle that they are specifically testing on. The test is also about general knowledge of the rules of the road. The test consists of a few graded turns, passing through intersections, stopping at intersections, speed control, lane control, road signs, railroad crossings, simulating and explaining going up and then down a steep grade, and a few other things. The truck is simply a work tool. The test is about the drivers and their skill level, not about the truck and its equipment.

If you are driving your own truck during the test, it's no different than driving someone else's truck. The skills and knowledge of that vehicle and its systems are being tested. If you are so unskilled that you cannot shift the transmission properly, this shows that you lack the basic understanding and basic control of the equipment that you are testing on. Shifting affects EVERYTHING in the whole test. An examiner could fail you for being unsafe or so unskilled that you would be a possible danger to the general public. When a driver is "hunting and pecking" for gears, that means that his attention is not usually where it actually needs to be.

Shifting skills affect everything else that the new driver does while in the truck and on the CDL skills test. It's common for the driver to be concentrating on shifting so much that he will make some pretty bad mistakes while fighting the gears. Enough practice must be obtained for at least a basic understanding of how the transmission works, and how to read the tachometer and road speed to select the proper gear. The scoring system of the CDL skills test could mean that you lose a few points on the shifting, or fail the test because of the numerous things that you can miss or not do properly while looking for or grinding the gears.


What are the different colors of the airbrake airlines on tractors and semi-trailers and in what order are they connected and disconnected?


There are two airlines and one (on most applications) power cord on semi trucks. There is a standard color code for these airlines and their connectors (called glad hands). The standard color for these airlines and/or their glad hands is blue and red. Sometimes the glad hands themselves are painted if the hoses are black rubber lines. There are commonly used airlines made of plastic and the airlines themselves are actually molded in the colors of red and blue.

The RED airline is called the "Emergency line" or sometimes the "supply line." When the red air supply valve or button is pressed on the dash of the tractor, the air system of the tractor supplies air to the trailer through the airline to fill the air tanks in the trailer and release the spring pressure that keeps the spring brakes applied. When the pressure is enough (it varies in some trailers) the trailer brakes release and the trailer will roll. The pressure is normally about 120 PSI in the lines and the storage tanks. If there is a leak or mechanical problem and the system cannot hold pressure and the air pressure in the system drops to about 60 PSI, an alarm buzzer and/or light will come on to alert the driver of the problem. When or if the air pressure continues to drop to around 30 PSI, the air supply valve closes (pops out) and the air is cut off instantly to the trailer. This will cause the brakes to lock in the trailer, and if going down the road at any real speed a skid and or jackknife may occur!

The BLUE line is called the "service line." The service line provides the air to make the trailer brakes work. When you press on the foot brake or pull on the "hand valve" in the tractor, air travels down the service line and applies the trailer brakes. If somehow the blue line is not connected, disconnected, or is damaged or broken, the driver will not notice anything until they actually try to slow down or stop the truck. If you apply the brakes, air will rush out of the hose (or leak) instead of going into the trailer and brakes, making them totally ineffective or inoperable. The thing that the driver would notice first if pulling a loaded (heavy) trailer is that the truck is not slowing down as it should and the air gauges in the truck would show a dramatic air loss. This is one of the reasons for the brake check areas on the tops of mountains and grades for trucks. This gives the driver a place to check their brakes and air systems before starting down the grade.

There is really no certain way or order to hook the lines up. The best way to hook them up is far to near so you do not have to work around the other hoses. When removing the connectors they should be hooked to the tractor on the fixture provided or at least hooked together so they do not get dragged, and so water and other debris does not get into the air system. The electrical cord should also be stored out of the way.

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