Steering Linkage: Idler Arm
An idler arm is used in a parallelogram type steering system. Today's vehicles typically have either a parallelogram or a steering rack configuration. A parallelogram system will have a gearbox with a pitman arm attached to its sector shaft. The parts include the pitman arm, center link, idler arm, and the two tie rods.The idler arm is designed to keep the center link parallel to the road surface while allowing the link to swivel both left and right. It is set at the same angle and length as the pitman arm. The pitman arm is attached to the gearbox and turns the center link. The idler arm is designed to provide swivel movement while offering resistance in the up and down direction. This resistance is vital in maintaining a vehicles toe setting.
When steering linkage gets loose a vehicle will begin to shimmy and the steering will feel loose. The system consists of links with tapered holes and tapered ball joints that are fitted together and torqued to a specified amount. It is when the ball joints studs get loose in their bores or the holes in the links themselves get enlarged that looseness occurs. When either of these conditions occur the part must be replaced.
An idler arm has either a tapered hole or a ball joint on the end connecting to the center link and a mounting portion that is bolted to the frame or sub-frame. The ball joint portion can get loose in its bore or the hole may become enlarged requiring replacement. Sometimes the idler arm has bushings between the frame and the mount. These bushings as well as the mounting bolts should be checked for wear and looseness. Some mounts have adjustable slots. Always mark these mounts prior to removal.
The swivel portion of the idler arm wears resulting in upward and downward movement. This movement will change the vehicles toe setting resulting in shimmy, loose and sloppy steering, and feathered tire wear.
