7.2 Coupling and Uncoupling

7.2 Coupling and Uncoupling

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 air tank, and disconnect the emergency line. This will set the trailer emergency brakes (if the slack adjustor adjusters are correctly adjusted). Chock the wheels if you have any doubt about brakes.

Couple Tractor and First Semi-Trailer as Described Earlier

Caution: For the safest handling on the road, the more heavily loaded semi-trailer should be in first position behind the tractor. The lighter trailer should be in the rear.

A converter gear or dolly is a coupling device of one or two axles and a fifth wheel by which a semi-trailer 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. (Or, if the dolly has spring brakes, use the dolly parking brake control.)
• If the distance is not too great, roll the wheel dolly into position by hand so it is in line with the king pin.
• Or, use the tractor and first semi-trailer to pick up the converter dolly:
-Position combination as close as possible to converter dolly.
-Move only to rear of first semi-trailer 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 semi-trailer.
-Lower dolly support.
-Unhook dolly from first trailer.
-Wheel dolly into position in front of second trailer in line with the kingpin.

Connect Converter Dolly to Front Trailer
• Back first semi-trailer 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 Rear Trailer
• Make sure trailer brakes are locked and/or wheels chocked.
• Make sure trailer height is correct. (It must be slightly lower than the center of the fifth wheel, so trailer is raised slightly when dolly is pushed under.)
• Back converter dolly under rear trailer.
• Raise landing gear slightly off ground to prevent damage if trailer moves.
• Test coupling by pulling against pin of number two semi-trailer.
• Make visual check of coupling. (No space between upper and lower fifth wheel. Locking jaws closed on kingpin.)
• Connect safety chains, air hoses, and light cords.
• Close converter dolly air tank petcock.
• Close shut-off valves at rear of second trailer (service and emergency shut-offs).
• Open shut-off valves at rear of first trailer (and on dolly is so equipped).
• Raise landing gear completely.
• Charge trailers (push “air supply” knob in) and check for air at rear of second trailer by opening the emergency line shut-off. If air pressure isn’t there, something is wrong and the brakes won’t work.

Uncoupling Twin Trailers

Uncoupling Rear Trailer
• Park rig in a straight line on firm level ground.
• Apply parking brakes so rig won’t move.
• Chock wheels of second trailer if it doesn’t have spring brakes.
• Lower landing gear of second semi-trailer enough to remove some weight from dolly.
• Close air shut-offs at rear of first semi-trailer (and on dolly if so equipped).
• Disconnect all dolly air and electric lines and secure them.
• Release dolly brakes.
• Release converter dolly fifth wheel latch.
• Slowly pull tractor, fist semi-trailer, and dolly forward to pull dolly out from under rear semi-trailer.

Uncouple Converter Dolly
• Lower dolly landing gear.
• Disconnect safety chains.
• Apply converter gear spring brakes on chock wheels.
• Release pintle hook on first semi-trailer.
• Slowly pull clear of dolly.

Caution: 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.

Coupling & Uncoupling Triple Trailers

Couple Second and Third Trailers
• Couple second and third trailers using the method for coupling doubles.
• Uncouple tractor and pull away from second and third trailers.

Couple Tractor/First Semi-trailer to Second/Third Trailers
• Couple tractor to first trailer. Use the method already described for coupling tractor-semitrailers.
• Move converter dolly into position and couple first trailer to second trailer using the method for coupling doubles. Triples rig is now complete.

Uncouple Triple-Trailer Rig
• Uncouple third trailer by pulling the dolly out, then unhitching the dolly using the method for uncoupling doubles.
• Uncouple remainder of rig as you would any double-bottom rig 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. Lear the right way to couple the vehicle(s) you will drive according to the manufacturer and/or owner.

Safety First!