What to Know When Coupling and Uncoupling a Tractor-Trailer Rig
With nearly 3 million tractor-trailer rigs rolling on the roads in the United States each year, those outside the industry might not realize what an artform it is to match up the tractors with trailers.
While some trailers are loaded and unloaded at the point of delivery so coupling and uncoupling doesn’t happen at every stop, there are times when the tractor and trailer need to be separated and then reattached later. In some cases, the trailer is dropped at its destination for unloading, so the tractor can go on to the next job. Maintenance to either the tractor or the trailer may also be a reason to separate them.
To understand what it takes to perform this task properly, we’ve put together the following guide to learn more about the procedure, especially if there comes a time as a new driver when you need to know how to perform this skill.
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A Couple of Terms to Know
There are a number of terms used in the coupling/uncoupling process that we need to define in order to make it easier to understand:
- Landing Gear: A semi trailer’s landing gear is a system of retractable legs that support the trailer when it is detached from the tractor. These are crucial for supporting the trailer when loading and unloading, especially if the trailer is on uneven ground.
- Fifth Wheel: The coupling device attached to the tractor.
- Fifth Wheel Jaws: The locking device on the fifth wheel.
- King Pin: The metal pin on the trailer that attaches to the fifth wheel.
- Glad Hands: The couplers for the air brake system which securely link the pressurized air hoses and brake lines.
Let’s Get Hitched (Or Unhitched)
With the terminology defined, here’s a review of the steps it takes to couple and uncouple a tractor trailer.
For the record, it is possible for one person to couple and/or uncouple a tractor-trailer, but having a second person to guide the alignment and complete the connection is generally faster, safer, and easier. Just as you would exercise caution when learning the basics of truck loading for beginners, you should take things slowly. Since the coupling area is close to the cab, one person can drive the truck and the other can yell out commands on alignment. However, in a noisy environment, you may want to use walkie-talkies, cell phones, or hand signals. Once the connection has been made, the second person can call out to the driver to give a quick tug test to make sure the connection is secure.
When trying to do the procedure alone, the driver may have to get out of the cab several times to get the alignment right, make all of the necessary connections, then complete the tug test. As you can imagine, that takes more time and energy, although with practice, a good driver should be able to get the job done efficiently.
Uncoupling
Before starting the actual process, chock the rear tires of the trailer (one in front and one in back so the trailer doesn’t rock). Then, make sure that your parking brakes are on, that the tractor is in neutral, and that the engine is turned off. Ahead of dropping the landing gear, make sure that the ground below is level and free from debris, and also that it will be able to support the weight of the trailer (hard surface) once uncoupled from the cab.
There are two “gears” for the landing gear handle—high and low. Use the high gear for lowering the landing gear to make the process faster. You should only use the low gear when the landing gear is in contact with the ground. When raising or lowering a trailer, be sure to keep yourself away from where the handle turns to to prevent a collision or injury when it swings around.
When the landing gear feet are just touching the ground, secure the handle, disconnect the air and electrical lines and secure them to the back of the trailer, then get back in the trailer and hit the button in your cab to release the king pin. This usually takes about three seconds. Once you are notified it has released, pull up about 6 inches to make sure the trailer is on secure ground. Once you’re satisfied and believe all is good, you can pull completely forward.
Coupling
Before getting started, take a look at both the king pin and the fifth wheel to make sure both are in prime condition and not damaged. Also check to see that the fifth wheel jaws are in the open position. Next, check to make sure that the trailer is positioned to the proper height for the fifth wheel to slide into place. Then it’s just a matter of aligning the tractor with the trailer and backing in slowly until the fifth wheel is directly over the king pin. The fifth wheel jaws should lock onto the king pin, which you can test by doing a slow tug test, moving only a couple of inches forward so you don’t damage the landing gear.
Once you hear everything click together and the tug test looks successful, get out of the cab and do a visual inspection to see that the locking pin is fully engaged and that the jaws of the fifth wheel are fully clamped down. Once satisfied that all is well, you can pull up the landing gear and attach the glad hands.
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Drive On
Need a semi to put the information above to good use? Commercial Truck Trader has the largest online inventory of new and used trucks to choose from. When you’re ready to get connected, we’ve got the hookups so you can purchase a top vehicle or buy a heavy-duty trailer.
Barrett Baker
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