The kingpin of a trailer is a small but essential component. It’s responsible for coupling a trailer to a tractor, which means its one of the few things keeping a rig together on the road. Operators know that the kingpin is the last thing you want to go bad while you’re on the road, but how can you identify a bad kingpin before it becomes a problem? Here are 5 symptoms of a worn or bad kingpin to look out for every time you’re coupling or uncoupling a trailer:


1. Hard to Couple

If you’re having problems coupling a trailer on the tractor, it could be a sign that you have a bent kingpin or upper coupler.

A kingpin that is in great shape should make it easy to couple your tractor and trailer. So, if you’re noticing problems with a specific trailer, the kingpin could be to blame.

What’s the cause? In the case that you’re having trouble coupling your trailer, the issue could be a result of a worn or failing upper coupler structure.

Why fix it? If your kingpin or upper coupler are bent, not only are they making coupling more difficult, but they’re no longer supporting your trailer and cargo safely. This is an unsafe way to haul, and it’s also a leading cause of accelerated top plate surface wear.

In any case, the best solution is to have the upper coupler structure and kingpin inspected and replaced if possible. You’ll spend less in the long run by addressing the problem now rather than waiting for it to affect other parts of your rig.

2. Hard to Uncouple

Maybe your tractor and trailer coupled just fine, but now you’re having problems uncoupling them. This is a key sign of a bad kingpin. The symptoms here are similar to those that occur when it’s difficult to couple a trailer, and it’s also usually a sign of a bent kingpin or coupler.

This is another fix to make as soon as possible. If you’re unable to have the problem addressed, a bad kingpin can add significant wear to your tractor and fifth wheel. What’s more, it’s an unsafe way to haul. It’s always best to get a bent kingpin fixed as soon as possible.

3. Fifth Wheel Adjustment Will Not Tighten — Worn Down Shoulder

If you’re experiencing problems with your fifth wheel adjustment, it’s usually a sign of a bad kingpin. There are two issues that could be causing this, the first of which is a worn-down shoulder.

When the shoulder of the kingpin wears down, it becomes impossible for your fifth wheel adjustment to tighten securely. There’s not enough material for the fifth wheel to tighten against, and if you cannot tighten your fifth wheel adjustment, you cannot safely haul.

This is a sure sign of a worn kingpin in need of replacement. The best solution is to address this as soon as possible by installing a new kingpin.

4. Fifth Wheel Adjustment Will Not Tighten — Worn Down Throat

As mentioned, there are two key problems that will prevent a fifth wheel adjustment from tightening. The first was the worn-down shoulder, and the second is a worn-down kingpin throat. When this happens, the throat has become so worn down that there is nothing for the fifth wheel adjustment to tighten against.

This presents a similar problem to a worn-down kingpin shoulder, which is that the coupling cannot be safely secured. Here too, it’s essential that you replace the kingpin before using the trailer. It is unsafe to haul if the coupling cannot be secured properly.

5. Lack of Lubrication

The fifth and final symptom of a bad kingpin is a lack of lubrication. If a kingpin has been poorly lubricated, excessive wear can happen quickly — and excessive wear is a surefire sign of a bad kingpin.

The kingpin and fifth wheel should always be well lubricated to reduce grinding between the tractor and the tractor’s fifth wheel. If the kingpin is not properly lubricated, it will wear unevenly and prematurely, which can create unsafe hauling conditions.

Signs of poor kingpin lubrication include the galling of kingpin contact surfaces and premature wear. If you know that a kingpin is not at the end of its life but is showing significant wear, a lack of lubrication is likely the problem. Unfortunately, once worn down, and especially when worn down unevenly, and kingpin must be replaced to ensure the safety of the operator and the rig.

Invest in a Better Kingpin

Forget the symptoms of a bad kingpin when you invest in a better kingpin developed by experts in the commercial transportation industry. JOST kingpins have proven themselves mile after mile over the world’s most challenging roads. They’re built for quality, safety, and durability. If you’re ready to upgrade, we have the solutions you need. Find a dealer near you.