Knowing how to couple and uncouple correctly is basic to safe operation of doubles and triples. Wrong coupling and uncoupling can be very dangerous. Coupling and uncoupling steps for doubles and triples are listed below.
Coupling Twin Trailers
Secure Second (Rear) Trailer
If the second trailer doesn’t have spring brakes, drive the tractor close to the trailer, connect the emergency line, charge the trailer air tank, and disconnect the emergency line. This will set the trailer emergency brakes (if the slack adjusters are correctly adjusted). Chock the wheels if you have any doubt about the brakes.
For the safest handling on the road, the more heavily loaded semitrailer should be in first position behind the tractor, and the lighter trailer should be in the rear.
A converter gear on a dolly is a coupling device of one or two axles and a fifth wheel by which a semitrailer can be coupled to the rear of a tractor-trailer combination forming a double bottom rig.
Position Converter Dolly in Front of Second (Rear) Trailer
Release dolly brakes by opening the air tank petcock (valve), or if the dolly has spring brakes, use the dolly parking brake control.
If the distance is not too great, wheel the dolly into position by hand so it is in line with the kingpin. If the distance is too far between the dolly and the trailer, use the tractor and first semitrailer to pick up the converter dolly:
- Position combination as close as possible to converter dolly.
- Move dolly to rear of first semitrailer and couple it to the trailer.
- Lock pintle hook.
- Secure dolly support in raised position.
- Pull dolly into position as close as possible to nose of the second semitrailer.
- Lower the dolly support.
- Unhook the dolly from the first trailer.
- Wheel the dolly into position in front of the second trailer in line with the kingpin.
Connect Converter Dolly to Front Trailer
- Back first semitrailer into position in front of dolly tongue.
- Hook dolly to front trailer.
- Lock pintle hook.
- Secure converter gear support in raised position.
Connect Converter Dolly to the Rear Trailer
- Make sure the trailer brakes are locked and/or wheels chocked.
- Make sure the trailer height is correct (it must be slightly lower than the center of the fifth wheel, so the trailer is raised slightly when the dolly is pushed under it).
- Back the converter dolly under the rear trailer.
- Raise the landing gear slightly off of the ground to prevent damage if the trailer moves.
- Test the coupling by pulling against the pin of the second semitrailer.
- Make a visual check of coupling (no space between the trailer apron and the fifth wheel plate, and the locking jaws are closed around the kingpin).
- Connect the safety chains, air hoses, and light cords.
- Close the converter dolly air tank petcock (valve).
- Close the service and emergency air shut-off valves at the rear of the second trailer.
- Open the service and emergency air shut-off valves at rear of the first trailer and on the converter dolly (if so equipped).
- Raise the landing gear completely.
- Charge the trailer brakes (push “air supply” knob in), and check for air at rear of second trailer by opening the emergency air line shut-off. If air pressure isn't there, something is wrong and the brakes won't work.
Uncoupling Twin Trailers
Uncouple Rear Trailer
- Park the vehicle in a straight line on firm level ground.
- Apply the parking brakes so the vehicle won’t move.
- Chock the wheels of the second trailer if it doesn't have spring brakes.
- Lower the landing gear of the second semitrailer enough to remove some of the weight from the dolly.
- Close the air shut-off valves at the rear of the first semitrailer (and on the dolly if so equipped).
- Disconnect all of the dolly air and electric lines and secure them.
- Release the dolly brakes.
- Release converter dolly fifth wheel latch.
- Slowly drive the tractor forward with the first semitrailer and dolly still attached in order to pull the dolly out from under the rear semitrailer.
Uncouple Converter Dolly
- Lower the dolly landing gear.
- Disconnect the safety chains.
- Apply the converter gear spring brakes or chock the wheels.
- Release the pintle hook on the first semitrailer.
- Slowly pull clear of the dolly.
Never unlock the pintle hook with the dolly still under the rear trailer. The dolly tow bar may fly up, possibly causing injury, and making it very difficult to re-couple the equipment.
Coupling & Uncoupling Triple Trailers
Couple Tractor & First Semitrailer to Second, Third Trailers
- Couple the tractor to the first trailer. Use the method already described for coupling tractor-semitrailers.
- Move the converter dolly into position and couple first trailer to second trailer using the method for coupling doubles. The triple trailer combination is now complete.
Uncouple Triple-trailer Combination
- Uncouple the third trailer by pulling the dolly out, then unhitching the dolly using the method for uncoupling doubles.
- Uncouple the remainder of the vehicle as you would any double-bottom vehicle using the method already described.
Coupling & Uncoupling Other Combinations
The methods described so far apply to the more common tractor-trailer combinations. However, there are other ways of coupling and uncoupling the many types of truck-trailer and tractor-trailer combinations that are in use. There are too many to cover in this manual. You will need to learn the correct way to couple the vehicle(s) you will drive according to the manufacturer and/or owner specifications.
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