Don't ignore the fifth wheel

By: Lawrence Schäffler, Photography by: Lawrence Schäffler

Date: 21.03.2013

Despite their crucial role in keeping trucks and trailers operating as safe, harmonious units, fifth wheel couplings are often overlooked in preventative maintenance schedules. Regular inspections help to minimise the odds of failure

Don't ignore the fifth wheel

A complete failure of a fifth wheel coupling is rare but it's not unknown — and the result is usually pretty spectacular. Underlying causes are fairly straightforward: a lack of regular maintenance and/or abuse by operators.

"Ironically," says Rhys Harnett at Auckland's BPW Transport Efficiency, "one of our issues is that the component itself is a very robust, heavy-duty item which seldom gives problems.

"Sadly, that means many operators tend to ignore it — the classic 'if it ain't broke, don't fix it' syndrome. It also comes in for abuse because it's perceived as an ultra-tough item that will take any punishment unflinchingly."

BPW Transport Efficiency is the New Zealand distributor for Jost Werke, one of the world's four major manufacturers of fifth wheel couplings. The other three are SAF-Holland, Fontaine, and Georg Fischer.

Fifth wheels on heavy rigs fall into two basic types, says Harnett, those that are lubricated with grease, and those that aren't (they are instead fitted with teflon/urethane skid pads). All the manufacturers supply both types and both need regular inspections and maintenance.

Lubrication

"A common problem with the lubricated models is irregular or insufficient greasing," says Harnett. "All the manufacturers specify a maintenance programme — Jost recommends the mechanism is cleaned and greased every six months. As it happens, that ties in with the vehicle's COF inspection schedule, so it should be an easy routine to follow.

"Failure to clean and apply grease can damage the coupling. Typical results are scored plates and a corroded jaw locks up or seizes. Both can affect the reliability of the fifth wheel — as well as compromise the ease and speed of the coupling/uncoupling process itself."

He points out that while the COF inspection of the fifth wheel is only visual, Jost recommends that the unit's top plate is entirely removed at every six-monthly greasing schedule.

"It's important to clean it thoroughly (using an appropriate solvent) and inspect it for cracks, chafe, or damaged components. Most fifth wheels can be easily refurbished if there are worn parts — replacement kits are readily available."

While poor lubrication is one of the most common causes of imperfect fifth-wheel operation, the units can also be damaged by operator abuse. Problems range from the locking handle being bent (often by sloppy forklift operation during loading), to careless drivers failing to correctly match the height of the trailer's kingpin to the fifth wheel.

"A misaligned kingpin can damage the fifth wheel's locking mechanism — particularly if the driver reverses at speed. This prevents the mechanism operating smoothly, and sometimes it's so badly deformed it won't lock at all."

Poor alignment of the kingpin and fifth wheel can also damage the teflon pads on the non-lubrication models. "It's usually a high-hitch issue — when the height of the kingpin and fifth wheel are poorly matched," says Harnett.

"It's important to note the locking mechanism is not designed for a vertical load, only a horizontal load. So if the coupling attempt is affected by a high hitch, where the kingpin is dropped on to the locking mechanism, it can bend, severely affecting its integrity and operation."

The problem is often compounded when trailers and trucks are interchanged frequently, with different drivers using different settings. "Simply assuming the previous driver's setting on the trailer is fine for your truck is unwise."

The issue also arises when trailers are swapped between trucks with air and mechanical suspension. "Drivers of air models lower the suspension, reverse and hitch up and then reinstate the suspension. Drivers of trucks with mechanical suspension don't have that luxury, so it's important to check the height before reversing."

Grease vs teflon

While lubricated fifth wheels are still the most common, there is a growing shift to teflon models. Harnett says many operators don't like the mess associated with regular greasing schedules. There is also growing concern about the potential environmental impact of the process, where liberally-applied grease falls off the fifth wheel.

"An added deterrent is that lubricated models are more demanding at the six-monthly inspection, when the top plate is removed, cleaned, and inspected. Teflon models are obviously less messy and quicker to process, so the downtime and maintenance costs are lower." Lubricated fifth wheels are slightly cheaper than the teflon alternatives.

Kingpin wear

Wear and tear in the trailer-truck coupling also extends to the trailer's kingpin. "A common cause of premature kingpin wear is a poorly-adjusted locking mechanism," says Harnett, "where it's either too loose or too tight. If it's too loose the kingpin bangs every time the truck brakes and accelerates, damaging both the kingpin and the locking jaws. If it's too tight the chafe, scoring and wear will be excessive."

He points out that the play between the kingpin and locking jaws is easy to adjust and can even be done without unhitching the trailer. Most operators use a dummy kingpin to set the tolerance.

Until 2011, operators were compelled to replace kingpins at 100,000km intervals. The NZ Transport Agency changed the legislation in April of that year, introducing a new rule (Heavy Vehicles Amendment 2011 - Rule 31002/4) which stipulates that the kingpins need to be inspected and only replaced if necessary.

The objective of the rule is to: "remove the requirement for a kingpin to be tested or replaced every 100,000 kilometres. This requirement is considered to be unnecessary as the improper modification or poor manufacture of kingpins is covered by other rules. This change will reduce compliance costs, without reducing safety."

Extending the life and improving the performance of a fifth wheel, says Harnett, comes down to basic but regular maintenance — inspections and proper lubrication.

"I would also encourage drivers to get out of the cab after hitching and closely inspect the coupling to ensure that it's correctly engaged. Everyone carries out the 'tug test', but it's not foolproof.

"It's important to check that the safety latch is correctly deployed, and that there's no gap between the fifth wheel's top plate and trailer's rubbing plate. If there is, you have a problem."

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