In a truck steering system, the steering gear receives the rotational input from the steering wheel. Most steering gears have a hydraulic input and output for steering assistance. The pitman arm is attached to the output gear of the steering gear.
source.image: Gary’s Tradition Auto
As the steering gear rotates, the ball joint end of the pitman arm moves horizontally across the car. This moves the steering linkage back and forth in the direction the vehicle is to be steered.
A motor vehicle’s steering system contains the following basic parts: Steering wheel, Steering shaft and Column, Tie rods, rack, idler arms, Pitman arm, and drag or center link.
The idler arm provides support for the steering linkage. Inner and outer tie rods are attached to the ends of the steering linkage which attach to the steering knuckle.