Kingpin Maintenance is a Recommended Practice for Fleets

“We’ve never done any maintenance on our kingpins before…” is something we commonly hear from fleet maintenance managers. When we hear this, we know that their fleet is going to have above normal wear and damage on their kingpins and will need a lot of repairs.

In fact, in the 25+ years, Kingpin Specialists has been repairing kingpins with our engineered solution we know that fleets that don’t have a kingpin maintenance program can have a 25% increase in repairs over fleets that do regularly maintain their kingpins.

Regular Inspections

An upper coupler can last the life of a trailer.  Equipment users can help to maximize coupler service life by monitoring the wear, damages, material degradation, and surface finish characteristics of the trailers in their fleet. 

The periodic inspection, measurement, and documentation of upper coupler and kingpin wear, characterized and sorted by fifth wheel and trailer manufacturer, can be helpful in the continuing maintenance of the fleet.

Upper couplers must be inspected (at minimum) as part of the Federal Annual Inspection, or whenever there is suspicion or indication of damage, wear, or out-of-service condition. A more frequent inspection may be needed if the trailer is older, used in trailer-on-flat car (TOFC) Service, used in severe-duty service, or subject to atypically corrosive environments.

Kingpin Wear

In our last article, we discussed how wear and damage to kingpins are unavoidable because anytime you have metal in contact with metal you have the conditions where damage can occur. This is why regular inspections are so important because it is the only way to manage the wear and damage that inevitably will occur.  

There are 4 main factors that contribute to wear rates:

  1. Environment. Includes road conditions, traffic, yard configuration, and territory serviced.
  2. Maintenance. Regular greasing, maintaining low wear variance, type of equipment.
  3. Volume. Size of loads, number of drop and hook, and the type of cargo.
  4. Compatibility. Fifth wheel compatibility (material type and hardness).

Every fleet works in dynamic conditions so the best way to manage the wear and damage on kingpins is to regularly inspect and repair kingpins as soon as possible to minimize the amount of damage that occurs to the rest of the fleet.

Repair Guidelines

Once you have discovered that a kingpin no longer meets the OEM specifications or is damaged and requires a repair what do you need to consider?

First, the welding process employed must be qualified, that is, proven to be capable of producing similar mechanical properties to OEM kingpins.  Various national and international standards exist and are suitable for qualifying welding procedures. 

These standards provide the guidelines for the methodology and types of tests that must be performed on the welding procedure.  Welders must also be qualified, that is, proven capable of duplicating the results of the procedure qualification. 

Second, the repair procedure involves a cleaning procedure and a preheat procedure where the temperature is controlled before the welding starts, during welding, and after welding is completed.

Third, there are several tests that must be conducted to ensure that the repair procedure meets OEM and safety specifications and will last and be safe. These tests include mechanical testing, hardness tests, bend tests, impact tests, fatigue testing per SAE requirements, weld macro sections, and weld sequence for each diameter to be overlaid, and finally machining and final surface finish inspection.

Qualification of the Welder

Not only do all of the above repair guidelines and tests need to be met to repair a kingpin properly but most fleets do not have welders that are certified to do these repairs. That is why Kingpin Specialists provides a mobile nationwide service so that fleets can regularly have their trailers inspected and kingpins repaired when needed.

Over the years we have seen many uncertified welders perform repairs on kingpins and bolster plates that have resulted in additional damage being done to the fleets assets and creating a situation where the uncertified repairs put the public, the drivers, and the fleet at risk.

A Complete Solution

It is very important that kingpin repairs are done by a certified welder with a repair procedure that meets all the OEM and SAE specifications. Kingpins are often ignored and when they are repaired, they are often repaired by uncertified welders, either extreme is a recipe for added repair costs, unscheduled downtime, and potential disaster.

Kingpin Specialists has an engineered solution that meets all the requirements and is performed by certified welders. 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? Call us at 1-888-221-7774 or email us at

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