The kingpins on a semi-truck are the large pins that connect the truck's axle to the steering knuckle. The kingpins must be strong enough to handle the weight of the truck and trailer, as well as the forces exerted on them when turning. Over time, however, they can become worn down and need to be replaced.
There are a few signs that it may be time to replace your kingpins. If you notice any play in the steering, or if it feels like the front end of the truck is wobbling, these could be indicative of worn kingpins. You should also check for wear at the point where the pin meets the axle housing; if there is any scoring or pitting, this is another sign that replacement is necessary.
If you're not sure whether your kingpins need to be replaced, it's best to have a professional mechanic take a look. They will be able to tell you for sure whether replacement is needed, and can also install new kingpins if necessary.