The suspension system has two purposes. The first purpose most noticeable to the driver and passengers is to provide a comfortable ride for the occupants and any cargo. The second purpose is to maintain the stability,handling,and braking of the vehicle as it travels.
Types of Suspension Systems
The most common types of suspensions are dependent and independent.
Dependent suspensions
Dependent suspensions rigidly connect the wheels that are across from one another. This means it is possible for one wheel position to be affected by the position of the wheel on the other side. The easiest way to recognize a dependent suspension is to look for a solid axle.
Independent suspensions
Independent suspensions allow the wheels across from one another to move separately. There are many versions of the independent suspension. These versions will not be discussed here to maintain clarity. More than one type of suspension may be used on one vehicle.
The parts of the suspension are:
- “Live” or solid axle
- Subframe
- Springs—leaf,coil,air,and torsion bar
- Shock absorber
- Strut
- Panhard rod,Watts linkage
- Upper control arm
- Lower control arm
- Radius arm
- Ball joint
- Sway bar
- Sway bar bushing
- Sway bar bushing bracket
- End link
- Wheels
Not all of these parts will be used on all suspensions. There are a variety of combinations that vehicle engineers use depending on the type of vehicle being designed and the purpose it will serve.
“Live”or Solid Axle
The solid axle performs two duties. It transfers the power from the transmission to the wheels and provides a place for the suspension to be mounted. Read more about solid axles here.
Subframe
The subframe can be used to carry the engine,transmission,steering,and suspension system components. It is usually a square or tubular frame that bolts to the body of the vehicle. Subframes can be found under the front or rear of the vehicle.
Springs
Springs absorb the bumps in the road. They provide a comfortable ride for the occupants and luggage. There are several types of springs. These types are:
Leaf
Leaf springs are the oldest version of springs. They are made of several increasingly shorter layers of metal sandwiched together. They attach the axle to the frame.
Coil
Coil springs are a coiled piece of metal rod. They are generally used on solid axles,struts,and various other types of suspensions.
Air
Air springs are rubber bags inflated with air. This type of spring can control the height of the vehicle when loaded or unloaded. Air springs can be found as a stand alone spring or as part of a strut.
Torsion Bar
Torsion bars are a special type of spring because they are a rod that twists to provide the dampening effect.
Shock Absorber
Shock absorbers are used to dampen the effects of the springs. Since springs can bounce in both directions the shock absorber is filled with a gas and oil to control the bouncing effect.
Strut
Struts are a combination or an assembly of the spring and shock. When located on the front wheels,the upper part of the strut has a bearing that allows the wheels to turn. Some vehicles require the strut tower to be drilled out to adjust the strut when performing an alignment.
Panhard Rod or Watts Linkage
The panhard rod or watts linkage is a bar or set of bars that keep the axle from shifting side to side. This keeps the axle centrally located.
Upper Control Arm
The upper control arm serves as a mounting point for the top of the steering knuckle. It is mounted to the frame or body on one end and the other end is attached to the knuckle with a ball joint. The upper control arm mounting points can be used to adjust caster and camber when performing an alignment.
Lower Control Arm
The lower control arm performs the same function as the upper control arm. It is mounted in a similar manner as the upper control arm. It is generally not used for alignment adjustments.
Radius Arm
The radius arm is used to control the forward and rearward movement of the wheels. It is generally connected to the lower control arm on one end and the frame on the other.
Ball Joint
The ball joint allows a component to pivot 360 degrees. It is generally found on upper and lower control arms. The ball joints are what the steering knuckle attaches to.
Sway Bar
The sway bar transfers the load of the vehicle in a turn from one side to the other. It is mounted to the lower control arms via the end links. It is supported by the sway bar bushings and mounts that are located on the frame of the vehicle.
Sway Bar Bushing
The sway bar bushings allow the sway bar to pivot as the vehicle travels over bumps and turns. They may be made out of rubber,polyurethane or other materials. There are generally two bushings per sway bar.
Sway Bar Bushing Bracket
The sway bar bushing bracket fits around the sway bar bushing and bolts to the frame. This bracket holds the sway bar bushing and bar in place.
End Link
The end links connect the sway bar to the lower control arm. There is one on each end of the sway bar. An end link is a combination of parts. It generally consists of a long bolt,four bushings,a sleeve,and a nut.
Wheels
A wheel is a rim with a tire mounted on it. The wheels bolt to the hub on the steering knuckle. Lug nuts or lug studs are used to attach the wheel to the hub.