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The Pitman arm is the steering box transfer linkage in a Pitman type vehicle steering mechanism. It is the component in the system which translates the radial motion of the steering column or shaft into the linear motion to turn the wheels. The Pitman arm is the first of three angular rotation linkages that transfer the steering box inputs to the track rod which in turn moves the left and right tie rods and their respective wheels. The other two linkages are the idler arms which are attached to the ends of the track rod as stabilizers. The Pitman arm is a crucial part of a vehicle's steering system and, when worn or damaged, can cause potentially catastrophic loss of steering control.
Pitman steering systems are most commonly found on older vehicles and heavy trucks. Most newer models feature variations of rack and pinion type steering mechanisms. The Pitman system is, however, robust and reliable when maintained correctly. These systems typically consist of a rod that runs from the steering wheel, through the forward firewall, and into the engine compartment. Here it enters a steering box where the axis of its movement is turned at 90 degrees to drive a short transfer shaft by means of a worm gear and nut or roller arrangement.
The Pitman arm is a flat, off-set lever which is attached to the transfer shaft at one end and a ball joint on its other. A linkage arm attaches to this ball joint and a similar joint on the track rod. The track rod is, in turn, attached with ball joints to a set of tie rods on either end. The tie rods then connect to the wheels via articulated steering arms. When the steering wheel is turned, the shaft moves the Pitman arm through a short arc which then pulls the track rod to the left or right.
When the track rod moves, so do the tie rod/steering arm assemblies which cause both wheels to turn in the same direction and steer the vehicle. The track rod is also supported at either end by a pair of idler arms which keep the track/tie rod assembly stable and at the correct height. The Pitman arm thus represents the main actuator for the linear steering movement in Pitman steering systems. It then goes without saying that a worn or damaged Pitman arm will cause a loss of steering sensitivity or worse, i.e., a total loss of directional control over the vehicle. This makes the regular inspection and maintenance of this critical linkage a must for any vehicle maintenance regimen.
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