Bangiong Sound Between Fifith Wheel and Kingpin

Commercial Trailer is Making a Banging Sound Between the Kingpin and Fifth Wheel

Did you know that thousands of truck drivers have a problem with the connection between their semi-truck and trailer? To make matters worse, when they question it, they are often told it is not a problem!

What is the problem exactly?

Fifth wheels and kingpins are made of steel. When steel meets steel, you inevitably get wear and damage. This wear creates slop or a gap between the connection assemblies. As the tractor-trailer begins to move or comes to a stop, you feel a secondary shift of momentum.

This occurs as the connection components are stressed and the pin shifts its position within the fifth wheel jaws.  Connection component wear is unavoidable, but it is also manageable. The problem is that connection components, especially maintenance and repairs on kingpins, are largely overlooked industry-wide.

The Trailer is Making a Banging Sound

One driver posted the following on

“When starting to move from a stop there is a considerable amount of jerk, then while shifting a pretty good slam (as the trailer moves forward). This happens any time the tractor slows down and then speeds up. As far as I can tell there is no side-to-side movement but front-to-back…”

This driver has correctly identified that there is a problem with the connection between the semi-truck and trailer. But when he spoke to the company mechanic, he was not treated very well.

“I brought this to the company mechanic, and they scoffed at me and made me feel like an idiot. He said it moves about an inch and says that is fine (it feels like it could be moving more but I am not back there to see), he also claims he once hauled heavy equipment and had 4”- 5” of play and that was fine too. I am a new driver for them, and I admit I don’t have a ton of experience but as far as I know there shouldn’t be much play if any.”

Connection Issues Affect the Entire Fleet

This is an example where the driver correctly identified a problem, and the mechanic was misinformed. The driver understood the potential safety implications. He concludes, “I don’t want to drop my trailer in an intersection or anywhere on the road for that matter.”

The mechanic is failing to realize that when the connection between a fifth wheel on the semi-truck and the kingpin on a trailer is not within the OE specifications, the result of this variance causes further damage to both parts of the connection system. When those damaged units are connected to other units, they do damage to additional units. The problem quickly spreads fleet wide. 

The Proper Connection Specifications

Both the fifth wheel jaws and kingpin have a manufacture tolerance of one eight of an inch of wear. Combined, they have an overall maximum wear tolerance of one fourth of an inch. This may seem like a small amount of wear, but for the connection component to operate effectively and safely, they need to be within these tolerances.

Performing Fleet Evaluations

At Kingpin Specialists, we spend time educating fleets about the importance of having a regular kingpin evaluation process in place. Identifying wear on kingpins, before the trailer starts banging around, is critical. By identifying the wear early, steps can be taken to repair the kingpin and return it to OE specifications. This ensures that the fleet is safely operating and that more damage is not being done to other units in the fleet.

Kingpin Specialists has an engineered solution that is performed by welders certified in the specific weld application needed to refurbish the kingpin. This method is a proven tested engineered process.  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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