The two most common types of steering linkage are parallelism and rack and pinion. Parallelism steering linkage uses the pitman arm and idler arm to support the center link, forming a parallelogram. Tie rods connect a center link to the steering knuckles. In a rack and pinion steering system, the rack takes the place of the center link. It moves back and forth across the pinion, and tie rods connect it to the steering knuckles.
From the ASE A4 Task List:
Inspect and adjust front and rear steering linkage geometry (including parallelism and ride height).
In a parallelism steering linkage, the vehicle steers smoothly when the center link is parallel to the ground that is parallelism. If the center link is not parallel, the cause may be a bent or incorrectly positioned idler or pitman arm, which affects tie rod position, which leads to bump steer and an unequal turning radius.
Check parallelism after you replace parts in the steering linkage.
First, make sure ride height is equal on each side of the vehicle, that tire pressures are correct and that the vehicle is parked on a level surface.
Position the wheels straight ahead and center the steering gear.
Locate the points where the pitman and idler arms connect the center link and measure the distance from these points to the ground. Some center links have flat-machined surfaces for making these measurements.
The distance from the pitman arm side and the idler arm side of the center link to the ground should not differ by more than 0.06 inch (1.5 mm).
To adjust parallelism, raise the vehicle on a frame-contact hoist. Then, depending on the vehicle, either loosen the idler arm mounting bolts and reposition the arm in the slots on the frame, or turn a threaded bushing at the base of the idler arm mounting bracket to change idler arm position.
Separating and Installing Steering Links
Replace steering links if their ball joints are worn because the wear causes loose steering and wander or if the joint dust covers are ripped or damaged. The dust cover prevents joint damage and lubricant leaks.
To remove a link from the steering linkage, separate the ball joints that connect to other links at each end.
ASE A4 Test Prep Online Exclusive: Ball Joints
Technician A: “Excessive radial play found during a ball joint wear inspection indicates a worn load carrying ball joint.
Technician B: “Ball joint wear must be checked with the suspension fully loaded.”
Who is right?
Check out this ball joint tutorial from AVI for the answer. And for more AVI Test Prep Videos, head to www.avitestprep.com