Idler Arm Function and Symptoms

Parallelogram steering systems have an idler arm opposite of the pitman arm. It fixes the center link preventing it from moving and flexing as the vehicle travels over bumps and turns in the road. Today's vehicles typically have either a parallelogram or a rack and pinion steering system. The parts of parallelogram steering systems include the pitman arm, center link, idler arm, and the two tie rods.

Parallelogram steering linkage with an idler arm.

The idler arm is designed to keep the center link parallel to the road surface while allowing the connection to swivel both left and right. The pitman arm is attached to the gearbox; it turns the center link as the driver steers the vehicle. The idler arm is designed to provide swivel movement. It resists up and down movement. This resistance is vital in maintaining a vehicle's toe setting.

Tie rods

When steering linkage gets loose, a vehicle will begin to shimmy. The steering wheel 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.

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 before removal.