Trailer Magazine


Maintaining strong connections

  • From the January 2020 issue.
Maintaining strong connections

The most important part of a prime mover and semi- or multi-trailer combination, according to JOST Australia, is the often-overlooked device that actually locks the vehicles together. The fifth wheel mounted on the back of the prime mover, B-double lead trailer or road train convertor dolly is a critical component for the safe operation of all articulated combinations.

In an industry that boasts some large pieces of equipment, sometimes the smaller components don’t get much attention. However, it’s important to remember that components like fifth wheel couplings have the big responsibility of holding everything together.

Operators of heavy vehicles need to know and understand how components like fifth wheel couplings actually work and how to carry out the necessary checks to ensure that the fifth wheel is correctly coupled to the trailer kingpin. As Bob Martin, National Training Manager at JOST Australia explains, every JOST fifth wheel in the range features a one-piece lock jaw that locks around the trailer kingpin, backed by a lock bar that positions behind the lock jaw. The lock bar slides across from one side of the fifth wheel to the other, forming a positive fail-safe lock behind the lock jaw.

First and foremost, when coupling up to trailers, drivers must ensure that the fifth wheel is fully open which means the handle is fully extended. The driver then reverses the prime mover, lead trailer or road train converter dolly under the trailer skid plate, stopping short of the trailer kingpin.

Then the driver either raises the air suspension of the prime mover, trailer or dolly or lowers the trailer skid plate height by retracting the landing legs to ensure the trailer skid plate is in contact with the fifth wheel top surface. The trailer kingpin should still be visible at this stage.

It is also advisable to raise the trailer landing legs 50mm to 100mm off the ground, to avoid damage to the legs when completing the coupling procedure.

At this point the driver gets back into the prime mover and reverses steadily until the spring-loaded lock jaw fastens fully around the trailer kingpin. JOST recommends that while the prime mover is still in reverse gear, the driver should ease backwards one more time in reverse, to ensure that the trailer kingpin is fully seated in the fifth wheel.  Another important part of the coupling procedure is the ‘tug test’ where once coupled and while the trailer brakes are still applied, the driver selects low gear and eases the clutch to ensure the jaw and lock bar are fully engaged.

It must, however, be noted that performing the tug test does not mean that the driver doesn’t have to get back out of the prime mover and perform the three critical visual checks. Coupling of fifth wheels to trailers requires visual inspections and the driver cannot rely on audible noises alone.

JOST Australia provides a Coupling Code with every fifth wheel it sells and fleet operators also have their own coupling procedures that drivers must follow. Regardless of which procedure the driver uses to couple up, once coupled JOST recommends that the driver gets out of the vehicle and carries out three important visual checks to verify that the fifth wheel is correctly coupled.

The first of the three checks is to ensure that the trailer skid plate is in full contact with the fifth wheel top surface with NO air gap between the two surfaces.

The second, but equally important check is to ensure that the fifth wheel handle has fully retracted into the fifth wheel casting. Nearly every unit in the JOST range has a spring-loaded secondary safety latch that drops down in front of the handle, to lock the handle into the fifth wheel casting. If the safety latch is not down, the fifth wheel is not coupled correctly.

The third check is to ensure that the lock bar has slid all the way across the throat of the fifth wheel, behind the lock jaw. Even in the daytime, a torch may be required to see up into the rear section of the fifth wheel. To assist drivers with this safety checking procedure, some fleets are now positioning a work light at the rear of the prime mover chassis, which when illuminated lights up the rear of the fifth wheel.

The above coupling procedure requires drivers to alight from the prime mover twice, the first time prior to coupling up to the trailer kingpin, to visually check that the fifth wheel is open, the trailer skid plate is in contact with the fifth wheel top surface, the kingpin is visible and the trailer landing legs are raised off the ground. 

Once coupled, the driver needs to alight from the vehicle one more time and carry out the visual checks: No air gap, handle is fully in with secondary safety latch down and the lock bar is all the way across the rear of the lockjaw.

If these three visual checks are completed and the correct outcome verified, the driver can be assured that he or she will not drop a trailer from a JOST fifth wheel equipped prime mover, trailer or dolly.

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