Steering and suspension parts such as ball joints, tie rod ends, idler arms, control arms and steering racks may have to be replaced if worn or damaged. Other parts such as shocks, struts, springs, sway bars and control arm bushings may be replaced to restore like-new handling and ride control or to upgrade handing performance.
Ball joints connect the control arms to the steering knuckle. Replacement is required when play exceeds specifications. On some vehicles, the ball joint is part of the control arm and must be replaced as an assembly. Greasable ball joints are available for many truck applications.
Tie rod ends connect the steering linkage tie rods to arms on the steering knuckles. If worn, they can cause steering looseness and tire wear. Left and right side tie rod ends are usually different and may have reversed threads. Tie rods can be replaced individually, but on high-mileage vehicles it may be necessary to replace all of the tie rod ends and center link (if used) at the same time.
Idler arms are used with recirculating ball/parallelogram steering systems to maintain the proper alignment of the steering linkage. Mounted on the opposite side from the steering box and pitman arm, the idler arm pivots when the wheels are steered. Wear or looseness in the idler arm can cause steering play and wander.
Most late-model cars and trucks have power rack and pinion steering. Fluid leaks and center wear are common problems that require rack replacement. Short racks do not include new tie rod ends but long racks do. New rack mounts also are recommended, along with a power steering system flush. Leaks in the power steering hoses between the rack and power steering pump require new hoses and seals.
Shock absorbers and struts dampen suspension motions to improve ride control and handling. The shock absorber is mounted near the wheel and connected to one of the control arms. A strut is often part of the suspension itself, replacing the upper control arm and spring, though it may be a separate component on vehicles with wishbone suspensions. Inside shocks and struts is an oil-filled cylinder with a piston and valves. Movement of the suspension forces the piston to push against the oil. This creates friction and resistance to dampen the suspension.
Two basic types: twin-tube and monotube. Twin-tube shocks have an oil reservoir around the outside of the piston chamber. Monotube shocks have no outer chamber. One end of the shock is filled with pressurized gas and a floating piston seal separates the gas charge from the oil. Both types of dampers are usually gas-charged to reduce foaming and shock fade. High-pressure twin-tube shocks/struts are
often used for performance handling applications.
Shocks and struts are usually replaced in pairs. Preassembled struts that come with new springs and upper bearing plates make installation easier and eliminate the need for a spring compressor.