Diagnosing a Worn Kingpin

Improper lubrication of kingpin bushings can cause kingpin contact points to begin to wear at the steering knuckle. You will notice signs of kingpin and bushing failure from incorrect vehicle alignment, premature and uneven front tyre wear and rough handling. Experiencing these symptoms while driving may result in a shaking cab or steering wheel. Because of the potential for further damage and operator safety risks, properly diagnosing and repairing worn kingpins, bushings and tie rods needs to be addressed promptly. 

After experiencing symptoms of a kingpin and bushing failure, additional diagnoses must be done to rule out other wheel assembly issues that may also cause similar symptoms. An easy way to help determine a worn kingpin is to conduct a kingpin wear inspection. 

Before beginning, make sure to always review and follow the axle manufacture and company maintenance and procedure manuals. Kingpin wear inspection requires that no weight be on the axle; so jacking up the front of the truck is required. Follow truck-lifting procedures in your vehicle’s operating manual to properly lift the truck. 

After the truck is lifted and no weight is on the axle, remove the wheels and tyres. Tighten the wheel bearing to eliminate any play that may be related to a loose wheel bearing.  Another way is to have a helper apply the service brake to differentiate between wheel bearing and kingpin bushing wear. Try moving the wheel left to right and top to bottom and up and down. If the wheel has any play you may have an issue likely caused by a worn kingpin.  Use a dial indicator to measure, axial and lateral movement should not exceed 3.2 mm (1/8 or .120 in).

“It’s an 8-hour job to ream the bushing and replace the kingpin. The good news is the kingpins have a life of 1,200,000 km (750,000 miles), so with good maintenance they would only need to be replaced once during a truck’s lifetime,” said Duane Rasmussen, Instructor, Medium/Heavy Truck Technology, Hennepin Technical College. “Kingpins and bushing replacement are rarely covered under warranty, because it always relates to lack of preventive maintenance.”

Nothing lasts forever, even if these parts have been greased every day. However, the kingpins and tie rods can wear out extremely fast if they’re not greased on a regular basis. The cost for a kit containing bushings and kingpins can range from $500 to $1,500 and replacing them is very time consuming. Graco automatic lubrication systems can help you properly lubricate kingpin bushings, resulting in a much greater reduction in kingpin failures caused by improper lubrication.