Trailer Upper Coupler Least-Maintained Connection Component

The trailer upper coupler is the least maintained connection component and has been ignored for decades which is costing fleets more than they realize.

First released in August of 2008, the Technology and Maintenance Council’s RP 750 report was an attempt to raise awareness of growing concerns about trailer upper coupler and kingpin maintenance.

Unfortunately, even since the release of this report on the recommended practices for maintaining the upper coupler structure of commercial trailers equipped with two-inch kingpins, kingpin maintenance has not been given the importance it requires.

The task force’s co-chair, Bill Wahlin, VP of Engineering for Wisconsin-based Stoughton Trailers stated that fleet technicians needed to be aware of possible problems.

“Some fleets are going to use this as a tool to train their technicians and their drivers what to look for, and that goes a long way.”

Trailer Upper Coupler Are Often Ignored

The task force’s other co-chair, Rob Nissen echoes this opinion. The manager of technical service/training pointed out that the upper coupler and fifth wheel have consistently been two of the least-maintained components on a truck.

“The industry is in the frame of mind that it’s pretty much maintenance-free–it’s put together by the OEM, and once it’s put together it’s like there forever.” This is, however, not the case.

As we service fleets across the nation it is not uncommon for us to come across a fleet with 60% or more of the fleet is near and/or past the manufacturer’s operating threshold.

Trailers in a Yard

This doesn’t happen overnight but rather is the after effect of years of use where wear rates increase as the fleet ages and new equipment wears faster as it is integrated with older equipment that has not been maintained effectively.

During an annual inspection it is imperative that the kingpin grease is cleared off and the structural integrity is evaluated on the entire upper coupler assembly.  The cleaned kingpin needs to be inspected for squareness and wear.

If any area of the pin exceeds the manufacturer’s wear thresholds or is damaged, corrective action should be taken so the wear doesn’t impact other equipment in the fleet.

What Happens If Wear Is Not Corrected?

In an article on Goliath Business News, Nissen brought up this true story to accentuate the problem: “So this guy has a dry bulk tanker and he goes around the curve–his story is he was taking the curve at 10 miles an hour and looked in his mirror and saw the tanker going over.

The fifth wheel stayed intact and locked and it severed the lower diameter (head) of that kingpin apart–it snapped it right in half, and the tanker went over. But when you looked at the condition of the kingpin after the accident, it probably should have been changed…”

Typical wear on a new kingpin for a refrigerated trailer is between .005”-.010” a year with a manufacturer’s maximum tolerance of .125”.  On average, a new refrigerated trailer’s kingpin should last around 10-15 years.

However, the more you stress the connection components the higher your wear rate. If a trailer has multiple stops per day, carries heavy loads, or has specialized equipment like liftgates, wear rates can run higher.

Add factors like liquid transportation and an aged fleet with high wear and you can see wear rates in the .015”-.030” range or more per year.

Without a preventive maintenance plan in place to address the higher wear aspects, your kingpins can reach their operational limit significantly faster than anticipated.

How to Avoid Damage to the Upper Coupler

There are a few common causes of wear on the kingpin and surrounding components. Sodium- and magnesium-chloride based agents have been used as de-icers over the past decade, and though not any more corrosive than previous mixtures, have proven to be more difficult to remove.

These agents, road grit, and the grease on the fifth wheel assembly form into a rubbing compound that not only wears down the locks, but the kingpin itself.

This minor wear and tear may not be seen as much of a problem initially, but over time it adds to the factors that stress and wear the connection components.

The majority of the wear comes from the daily operations and the connection and disconnection of the connection components.

Improper coupling where the connection components are not aligned when connection is made can create significant damage to the connection components.

That damage then can accelerate wear and impact other equipment in the fleet as the damaged equipment is utilized in daily operations. For this reason, training on the proper coupling and uncoupling of trailers is highly recommended.

Proper Lubrication

It’s obvious that the upper coupler, kingpin, and fifth wheel need to be properly lubricated. But it might not be obvious that grit and dirt can combine with grease to create an abrasive that will damage these components.

Lubrication is important for trailer upper couplers

The surfaces should be cleaned off and fresh grease applied with no exposed metal surfaces. A good lubricant is one that has the proper viscosity, protects from corrosion, and is resistant to oxidation, water, and weather.

Inspecting the Upper Coupler and Kingpin

The RP 750 Recommended Practice for inspecting upper couplers is thorough. The front, bottom, top, and sides of the upper coupler are checked for damage and corrosion.

The components should be cleaned of excess grease and grit, although water should not be used because it could cause corrosion.

The kingpin should also be inspected for squareness, proper height, wear and to ensure it is secure.  At a minimum inspection of the upper coupler, kingpin assembly, and fifth wheel jaws should be done yearly.

Time to Call the Kingpin Specialists

Without understanding the scope of the connection management issues affecting a fleet, it is impossible to quantify the real long-term costs. It is also difficult to make any meaningful progress in fixing the ongoing connection management issues.

Most in-house technicians do not have an engineered solution at their disposal, lack the experience and training required to repair kingpins effectively, and even misunderstand the relationship between the fifth wheel and kingpin.

If you are responsible for fleet maintenance on commercial vehicles, why not take the first step and have Kingpin Specialists perform an inspection and report on the condition of your fleet?

Contact us today for a free fleet evaluation.

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