Subject:
Steering knuckle:
The steering knuckle (also called knuckle or knuckle body) plays an important role in the suspension. It serves as the pivot point for the ball joint (at the bottom of the knuckle) and the track rod end. The shock absorber is clamped into the top of the knuckle, so it turns along with the steering movements. The wheel bearing is also mounted in the knuckle. The image shows part of the suspension in which the wheel bearing is mounted with 4 bolts, but a wheel bearing can also be pressed into the knuckle. In that case there are no bolts and special press tools must be used for removal and installation.
The image shows a steering knuckle from the front axle of a VW Golf (Mk 6).
Ball joint:
The steering knuckle in the image is now seen from the other side (from the inside). The ball joint is mounted at the bottom. This is the connection between the lower control arm of the suspension (to which the triangular plate with nuts is attached) and the knuckle itself. When steering, the track rod end pulls or pushes the knuckle around its axis. It pivots around the ball joint and moves the shock absorber along as it turns. Defects in the ball joint can be caused by a torn dust boot, driving (fast) over speed bumps or humps in the road, or extreme loads in the suspension (e.g. when driving up curbs).
