Welder Repairing a Structurally Mounted Kingpin on a Commercial Trailer

A Deep Dive into Structurally Mounted Kingpin Repair

How do you repair a structurally mounted kingpin that has been damaged or has wear that exceeds OEM specifications?

Replacing or Repairing a Structurally Mounted Kingpin

The trailer’s kingpin is the cornerstone of the connection between the tractor and trailer. The kingpin, which the majority of are composed of 8630 alloy steel, allows easy connection to the different fifth wheel manufacture assemblies, providing a secure connection for the transportation of large loads.

This grade of material has characteristics making it extremely tough (but not brittle), allowing it to absorb the stress during connections, while still having the resilience to wear compared to other metals compositions.

Although the connection points are made from high-strength material, during use, the connection components will experience stress and wear. You can help reduce the amount of wear and stress on connection components by servicing the equipment on a regular basis ensuring that the proper lubrication and jaw adjustments are maintained.

For operators of a single tractor-trailer, who do not experience daily disconnections and multiple stops, wear rates are typically low as the stress on the connection components is limited. On the other hand, when dealing with fleets that regularly interchange equipment, have daily disconnections and multiple stops, the wear rates can become unmanageable without proper maintenance.

Options for Structurally Mounted Kingpin Repair

If you are responsible for the repairs on your trailer or a fleet of trailers, it is always good to understand the options you have available to make the best decision that gives you the highest return on investment while ensuring industry standards are maintained.   

Below is a flow chart to highlight the available options.

Flow Chart Showing Kingpin Repair Procedure
Available Kingpin Repair Options

OEM and Aftermarket Direct Replacement

An OEM or equivalent aftermarket assembly will be a direct fit and will solve both structural integrity issues and kingpin replacement needs. This is one of the more costly ways to solve the issue. Downtime can become a factor due to both the repair shop availability to complete the repair and parts availability.

Caution should be taken with aftermarket assemblies to ensure that the assembly meets the required strength tests and is built to operational specifications.

Also, some manufacturers’ replacement upper coupler assemblies are a lower grade than the original equipment. It is important to ensure your replacement part meets your transportation needs.

For example, an OEM 3/8” bolster plate upper coupler assembly replacement could come with a 1/4“ thick bolster plate. Although the part is classified as a direct fit, the 1/4″ bolster plate will not have the same durability as the 3/8” originally installed bolster assembly.

Custom Fabrication

A custom fabricated upper coupler is where a repair or manufacturing shop builds an upper coupler from scratch to replace the existing assembly. This type of repair has become more common as parts availability is limited due to the effects of the current pandemic and subsequent supply chain disruptions.

A custom fabricated assembly can range you anywhere from $1.5K to $8K just for the bolster assembly, depending on the type of trailer and quality of the craftsmanship. While a properly constructed upper coupler assembly may run you more in cost than an OEM model, you may save on the time the trailer is out of service by going this route.

When looking for a custom fabrication you need to ensure that the work is performed by a certified welder who is tested and certified in the type of welds needed.

Structural Repair – Pin Replacement

Replacing the structurally mounted kingpin with a new kingpin requires a structural repair. The framing of the upper coupler assembly must be removed to replace the kingpin. It is then reinstalled with a new kingpin. It is important to ensure that it has the correct pin height, squareness, and adequate structural mounting. Structural repairs are common for trailers where the kingpin is integrated with the frame of the trailer.

When choosing this type of repair, be cautious that you do not can create a larger liability. Care must be taken when cutting out the old pin, as the work area is usually limited, and working through a small access hole makes it difficult to remove the old pin. Excess oxy/acetylene heat can oxidize the base metal in the bolster plate and cause the base metal to be weakened. Carbon arc is the better method to remove the old material.

Ensuring that the completed repairs meet the industry standards and manufacturer’s requirements is essential. There is a big difference between making a good weld and being able to create or repair critical components which requires a more in-depth engineering process.

One other issue with pin replacement is the pin itself. With the current supply chain issues, there is an increasing number of replacement kingpins on the market that are knockoffs or do not meet the SAE metallurgical standards. If you are purchasing a kingpin, ensure it has a stamped identification number and has been tested for hardness. Holland, Jost, and Wallace Forge are three of the most prominent manufacturers.

Kingpin Refurbishment

Refurbishing the structurally mounted kingpin with an engineered process gives the pin similar wear characteristics without invasively cutting into the structure of the trailer. When the bolster plate and framing are structurally sound, and the wear is limited to the kingpin, refurbishment is an ideal solution to maintain compliance and keep the fleets wear rate manageable.

Structurally mounted kingpin refurbishment is the process of rebuilding the kingpin’s operational dimensions by adding a spiral weld wrap and then machining the kingpin back to operational standards.

Using a fully insured, certified company, ensures structurally sound, safe results. Kingpin refurbishment is typically a 2-hour process from start to finish. The structurally mounted kingpin is repaired directly on the trailer, and it can go back into service immediately after the repairs have been completed.

Please note that if you choose this route, make sure that the company/technician has the proper certifications and knowledge to ensure the finished product meets or exceeds the standards of the OEM part.

With YouTube videos and parts supply issues, we have seen an increasing trend for individuals and repair companies attempting this type of repair, resulting in sub-standard repairs that do not meet compliance.

Structurally mounted kingpin refurbishment should not be done on a trailer that the upper coupler is structurally compromised (including cracks in the bolster plate). It should only be done by a company/technician who has been trained and certified through an engineered process established on the metallurgical composition, hardness, grain flow, and MFG operational specifications.

Unlike other repair methods, the refurbishment path allows for a preventative maintenance option that can help keep the wear rate manageable on the fleet and decreases excessive wear on all connection components in the fleet.

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 structurally mounted 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?

Call us at 1-888-221-7774 or email us at

Share this: