Idler Arm


A worn or damaged idler arm can cause steering instability, uneven tire wear, front-end shimmy, hard steering, excessive play in steering, or poor returnability.

Because an idler arm is the weakest link in a parallelogram steering system, it wears more quickly than the rest of the system

The procedure is simple for checking an idler arm for looseness or wear.

  • The suspension should be normally loaded on the ground or on an alignment rack. When raised by a frame contact hoist, the vehicle's steering linkage is allowed to hang, and proper testing cannot be done.
  • Check the idler arm ends for worn sockets or deteriorated bushings.
  • Grasp the center link firmly with your hand at the idler arm end.
Checking an idler arm. Courtesy of Moog Automotive.
  • Push up with approximately a 25-pound (110 N) load.
  • Pull down with the same load.
    • The allowable movement of the idler arm and support assembly in one direction is 1/8 inch (3 mm), for a total acceptable movement of 1/4 inch (6 mm).
    • The load can be accurately measured by using a dial indicator or pull spring scale located as near the center link end of the idler arm as possible.
    • Keep in mind that the test forces should not exceed 25 pounds (110 N), as even a new idler arm might be forced to show movement due to steel flexing when excessive pressure is applied.
    • It is also necessary that a scale or ruler be rested against the frame and used to determine the amount of movement.
    • Observers tend to overestimate the actual movement when a scale is not used.
    • The idler arm should always be replaced if it fails this test.
    • Jerking the right front wheel and tire assembly back and forth (causing an up- and down-movement in the idler arm) is not an acceptable method of checking, as there is no control on the amount of force being applied.