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 rack and pinion steering system. Parallelogram systems use a gear box with a pitman arm connected to the center link. It’s through the pitman arm that the gear box turns and moves the steering linkage. 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 providing resistance in the up and down direction. This resistance is vital in maintaining a vehicle's toe setting.

Parallelagram steering linkage with an idler arm.

When steering linkage gets loose, a vehicle will begin to shimmy as it travels down the road. As the steering wheel is first turned, it will feel loose and sloppy. The linkage system consists of links with tapered holes and tapered ball joints that are fitted together and torqued to a specified amount. When the ball joint studs get loose in their bores or the holes in the links themselves become enlarged, looseness occurs. These worn components must be replaced.

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 slotted mounts prior to removal.