King pin kits on HGVs: wear, testing, and replacement
The king pin is the vertical pin that passes through the axle beam and stub axle knuckle, providing the pivot axis for steering. The stub axle rotates around the king pin on bronze bushes that require lubrication at service intervals. When the bushes wear, the stub axle develops play on the king pin, which introduces looseness into the steering system and causes the tyre to wear across the tread edge.
Testing king pin wear requires the front axle to be lifted to unload the king pin. With the wheel off the ground, a dial gauge or ruler is positioned at the top of the tyre and the wheel is rocked fore and aft. DVSA guidance specifies maximum tolerances for annual test. King pin replacement requires pressing out the old pin and bushes and fitting new items with the correct interference fit.
Frequently Asked Questions
How do I test for king pin wear on an HGV?
Raise the front axle so the steer wheels are off the ground. Place a dial gauge at the tyre rim, or measure at the tyre contact patch. Have an assistant apply upward and downward force to the wheel at the hub while you measure the movement. Compare against the manufacturer's specified tolerance for king pin play.
What is the DVSA annual test limit for king pin play?
DVSA specifies maximum allowable play for steering pins as part of the annual test inspection criteria. The precise value depends on the axle design. For current limits, refer to DVSA's annual test inspection manual, Section 5 (Steering).
Do I need to replace the king pin and bushes at the same time?
Yes. The king pin and bushes wear together and should always be replaced as a complete kit. Fitting a new king pin into worn bushes, or new bushes onto a worn pin, will not restore the correct geometry.
Does Truckstop Group stock king pin kits for all HGV steer axle types?
We stock king pin kits for the main HGV makes. Call us on 01527 598 000 with your chassis number and axle specification to confirm the correct kit for your vehicle.
