Replacement Suspension Parts

Without a suspension system, you would not only have a bone shaking ride but little vehicle control as well. The tires would bounce in reaction to bumps, and tires that aren’t on the ground can’t direct, move or stop the vehicle. The suspension keeps the wheels in contact with the road surface for traction, steering and braking, so power gets to the ground and you can remain in control. All suspension systems have springs to absorb bumps and shock absorbers to control the action of the springs.

There are far too many suspension system designs for a detailed discussion here, but all can be divided into solid (beam) axle suspension and independent suspension. A solid axle is so called because the wheels on either side of the vehicle are linked by a rigid axle housing, and a bump in the road that affects one wheel will also disturb the wheel on the other side. Solid axles can be live axles that transmit power to the wheels or dead axles that do not, such as the rear axle on a front-wheel drive car. As the name implies, independent suspensions allow the wheels to move independently of each other, and the effect of a bump on the road encountered by one wheel will be isolated to that wheel and will not affect the wheel on the other side of the vehicle.

Independent suspensions use either struts or shock absorbers. A strut is a type of shock absorber that also serves as a supporting suspension member. There are modified struts where the springs are separate, but the most common type is the MacPherson strut, which incorporates a shock, spring and suspension member in one unit. When used at the front of the vehicle, the top of the strut is the upper steering pivot. Shock absorbers are used with control arm suspensions. Shocks and struts are the most commonly serviced suspension parts. Because they deteriorate gradually and degrade handling and ride quality, it is recommended that they be replaced after 50,000 miles, sooner if you experience a bouncy ride, nose diving when braking, and excessive body roll in turns.

Leaf springs are the oldest type of springs and generally used to both suspend and locate live axles. They are the springs of choice for hauling because they can carry heavy loads and the capacity can be easily increased by adding leaves. Coil springs are the most common type of spring in use today. They are much easier to tune for a specific ride and/or handling characteristics than leaf springs, making them ideal for performance vehicles. A torsion bar is a type of spring that twists in response to wheel movement. The advantage of torsion bars is that they can be adjusted to correct vehicle ride height. Air suspension air springs use compressed air to provide a smooth ride and suspension leveling. Self-leveling sensors provide ride height input to the air suspension system control module.

The wheels, springs, and shocks or struts are attached to the vehicle with suspension members called control arms. Control arms can be called different names according to the suspension system and where they are located on the vehicle, including short and long arms, radius arms, and trailing arms. In general they are made of stamped steel or aluminum and articulate by means of bushings and ball joints. The control arms themselves are generally very durable and usually only replaced if bent, but the bushings and ball joints wear and require replacement to eliminate play that can affect handling and alignment angles. Incorrect alignment angles can cause steering pull and tire wear. If conventional means of adjustment are inadequate an alignment kit can bring angles within specification.

The steering knuckles are the connection point for the front wheels, suspension members and steering linkage. The wheels may attach to spindles, which can be an integral part of the knuckle – this is a common arrangement for rear-wheel drive vehicles, or they may mount to hubs that bolt to the knuckles, and to which the drive axles are connected – typical for front-wheel drive and all-wheel drive vehicles. Ball joints allow the knuckles to move up and down with suspension movement and pivot in response to steering input. Panhard rods and track bars laterally locate solid axles within the vehicle body and prevent side-to-side movement. Sway bars are a type of torsion bar that connects the wheels on both sides of the vehicle to reduce body roll in turns.