King Pins

What is a Truck King Pin?

King Pins are the connection between your steer axle and the steering knuckle on heavy-duty, medium-duty, and older light-duty trucks with a straight axle. The king pins themselves are large, hardened steel pins that are centered in the axle beam. The king pins protrude out of the axle on the top and bottom where the steering knuckle wraps around the axle and king pin. The steering knuckle contains bi-metal bushings which wrap around the king pins and maintain a tight clearance to prevent steering play. The king pins and bushings manage a large amount of force while holding the knuckle in correct alignment.

What causes King pin wear?

Types of King Pin Kits

Performing a king pin rebush job is a major undertaking so it is best to be prepared for the task with a replacement king pin kit. There are two main options for king pin kits to accomplish the job of replacement.

Spiral bushing kits

Spiral bushing kits use a coiled, spiral-shaped bushing. These bushings can be installed by twisting into the spindle using an installation tool and they do not require reaming. Spiral kits are the ideal kit to use if you do not have the capability to press new bushing into the steering knuckles and ream them to fit the pins. You can avoid a machine shop using a spiral bushing kit so if you are servicing your own truck this is the kit to use.

Standard King Pin kits

Standard king pin kits use solid bi-metal bronze and steel bushings. Steel is used for the outer portion of the bushing to allow it to be pressed into the steering knuckle without deforming the inner bronze area. Bronze is used on the inside portion of the bushing due to its anti-friction and wear-resistant properties, bronze will only become damaged if lubrication is not present. The bushings included in a standard king pin kit will need to be reamed to fit the new pin after they are installed in the steering knuckle. Standard king pin kits are typically used by shops since special tools are required to line bore the bushings in the steering knuckle. If you are self-installing, it will require the assistance of a machine shop to fit the pins to the steering knuckle.

King pin kit components

King pin kits are specific for each axle model and the kits will include all necessary components to refurbish the axle and steering knuckle. Most king pin kits will include the following items:

• King pins – Large Hardened steel pins. These may be a single or double keeper (using one or two keeper bolts) The diameter and length of the pin are critical to finding the correct replacement kit. King pins are machined to fine tolerances to fit the axle precisely.
• Steering Knuckle bushings – Bushings will be included that are installed in the steering knuckle. There will be four bushings, two for each spindle. The type of kit that you have purchased will dictate whether you have spiral bushings or standard bi-metal bushings.
• Caps – King pin caps will be included when needed. The caps install in the top and bottom of the spindle and seal in grease while providing threads to install a grease zirc.
• Seals – Seals install at the top and bottom of the king pin to retain the grease. It is important to install the seal in the correct direction to allow the grease to flow through the bushings. Incorrectly installing the seals may block grease from reaching the bushings.
• Shims – Shims are used to control play between the steering knuckle and the axle. Shims will be used on the top of the axle between the spindle and the axle. Truck manufacturers will have specifications for each model on how much travel is allowable and shims will be added or removed to meet this specification.
• Keeper – Keepers are bolts that have a wedge-shaped head and retain the king pins in the axle. As the bolt is tightened the wedge squares the king pin against the axle.
• Thrust bearings – Thrust bearings are roller bearings that sit at the bottom of the axle against the steering knuckle. The weight on the axle rests on these bearings. Thrust bearings should be pre-packed before you install them to ensure proper lubrication.