Does a Bad Idler Arm Affect Tire Wear?

The idler arm is a component of the steering linkage in a vehicle that uses a conventional steering gearbox. It is not found on vehicles with rack and pinion steering. Its purpose is to support the steering linkage, so that it remains parallel at all times to allow free movement laterally.

Components of Conventional Steering Systems

Conventional steering utilizes a steering gearbox mounted on the drivers side frame rail. The steering column is connected directly to the top input shaft on the gearbox by a flexible rag joint. This joint isolates vibrations and a certain amount of steering feedback over rough terrain.

A shaft called the sector shaft protrudes from the bottom of the gearbox. A short pitman arm is mounted onto the sector shaft and is used to manipulate the linkages that provide directional control. The idler arm is mounted to the passenger side frame rail opposite the pitman arm.

A long bar called the centerlink is mounted to the pitman arm and supported on the opposite side by the idler arm. It is attached to both with a flexible joint. Each steering knuckle has a tie rod that extends to the center link and connected with a flexible joint. The tie rods are adjustable for the purpose of setting the toe during a wheel alignment.

Symptoms of a Worn Idler Arm

The idler arm is the weakest link in a parallelogram steering system due to the stress applied to it. Consequently, it will be the first of the steering linkages to wear out.

When an idler arm wears it becomes loose and gives the steering linkage excessive freeplay. This allows the vehicle to wander on the road with a perceptible amount of freeplay in the steering wheel. It will become difficult to maintain good directional control. The steering wheel will shake when traveling over rough terrain and usually an audible thump can be heard when encountering bumps.

A worn idler arm will cause the toe adjustment to change resulting in severe tread wear on the outside edges of the tires. It will also effect the way the steering wheel returns to center after a turn.

How to Check for a Worn Idler Arm

The most accurate way to test an idler arm is with the weight of the vehicle on the tires. The wheels must be straight ahead. Push up on the centerlink at the idler arm attachment point with 25 pounds of force. Make a note of the movement. There must not be over 1/8-inch of freeplay, either up or down. The vertical movement must be barely noticeable. Replace the idler arm, if any perceptible movement is found.

Replacing the Idler Arm

The process of replacing the idler arm is very simple. It is secured to the frame with two bolts and nuts. The bolts pass through the frame from the outside. Two access holes are provided in the frame for the bolts. The idler arm is secured to the center link with a tie rod end. When replacing the idler arm it is critical to abide by the manufacturers torque specifications on the two bolts securing it to the frame and on the tie rod end connection to the centerlink.