Idler Arm


Several styles of idler arms and brackets are used with parallelogram steering. The most common is an assembly in which the idler arm is integral with the mounting bracket. A worn idler arm is usually replaced as an idler arm and bracket assembly; in a few cases, only the idler arm or idler arm bushing is replaced.

When rubber idler arm bushings are used, the idler arms should be tightened onto the bracket with the tires in a straight-ahead position. As with rubber tie-rod ends, tightening the bushings in a turned position can cause a steering pull in the direction that the arm was when it was tightened and early failure of the bushing.

If the idler arm and pitman arm are not level to each other, the car will experience bump steer. Bump steer causes toe to change when going over bumps, which will cause tire wear.

To remove and replace an idler arm, you should:

  • Raise and support the car on a hoist or jackstands.
Some car models have changed the length of their idler arms during model changeover, and in some cases, the two different arms are almost interchangeable. If an idler arm is too short, it can go over center and lock the steering at the extreme position of a turn. Always check the new idler arm against the old one to ensure an exact replacement.
  • Remove the cotter pin and nut from the idler arm or center link stud.
  • Install a puller to break the stud taper and separate the idler arm from the center link.
  • Remove the bolts securing the idler arm bracket to the frame and remove the idler arm.
  • Clean and inspect the frame mounting location and the stud taper and mounting hole to make sure they are in good condition.
  • Place the new idler arm bracket in position, install the mounting bolts, and tighten the bolts and nuts to the correct torque.
    • Some idler arms have adjustable slots at the mounting bolts.
These slotted holes are for mounting an adjustable idler arm. Courtesy of Moog Automotive, Inc.
    • On these cars, steering linkage parallelism shoud be adjusted. With the steering exactly centered, measure the distance from the center tie-rod stud to the center of the upper control arm mounting/pivot bolt on each side of the car. Slide the idler arm up or down so these two measurements are the same or within 0.060 in. (1.5 mm) of each other.
    • Some idler arms use a threaded-style bushing; the idler arm can be unthreaded from the bracket. When installing this style of idler arm, the arm should be threaded as far as possible onto the bracket, but with enough room to rotate for normal operation. Thread the idler arm completely onto the bracket until it stops and then back it off one-half to one turn. Some idler arm assemblies have a setting dimension for this purpose.
  • Connect the idler arm to the center link, install the nut to the correct torque, and install the cotter pin.
  • Check toe and adjust, if necessary.