Suspension, how does it work?
Suspension assemblies are fitted between the vehicle chassis and the road wheels. Typically suspension assemblies consist of a spring, a damper and suspension linkages. The road spring absorbs the road surface bumps preventing shocks reaching the vehicle body. The dampers stop the road springs from oscillating or bouncing when they go over a bump in the road . Dampers are often referred to as shock absorbers but in fact it is the spring that absorbs the shock and the damper returns the spring to its resting position after deflecting. The suspension linkages connect the road wheels to the vehicle body and allow for suspension movement.
Suspension assemblies provide comfort to the passengers while transmitting the drive and braking forces that are applied to the road wheel to the vehicle body. The suspension ensures that the road wheel stay in contact with the road in all conditions maintaining full braking effort, vehicle stability, secure handling and the correct steering geometry while cornering.
With the rigid axle layout a fixed beam connects the wheels. This system is very strong but offers limited flexibility. This system was typically fitted to older rear wheel drive cars with the differential located in the rear axle. This system is more suited to light commercial vehicles, trucks and buses, where it is now used.
With this layout, each wheel has its own separate suspension assembly, and it is not affected by the movement of the other. Each suspension unit can operate independently, which provides better road holding and handling, greater comfort for the passengers and optimum steering geometry over all road surfaces.
Independent suspension is now fitted to the front of most modern cars with high end and performance cars having it fitted to the rear as well.
A common repair is to replace suspension coil springs; these springs can fracture, which reduces the ability of the spring to absorb shocks. If a spring has failed, usually, a clunking noise can be heard when going over bumps and a twanging noise apparent when cornering. It is essential to have this defect rectified immediately as road holding and safety will be compromised. In some cases the broken section of the spring can wedge against the tyre and cut a grove in the side wall.
When a damper starts to leak the damping effect is reduced and the unit must be replaced. If left unchecked most of the damper oil will escape and no damping effect will be provided. If a damper has failed the driver will usually experience a bouncy ride and the car will wallow into and out of bends. Efficient damping maintains stability, comfort and crucially ensures the road wheel remains in contact with the road surface.
Excess play and wear in suspension arm bushes and ball joints are frequent MOT failure items. Suspension arm bushes are typically metal-elastic in construction and it is usually the rubber centre that becomes de-bonded from the metal sleeve, which causes the excess movement. Other reasons for the bushes to fail include oil contamination to the rubber, causing it to soften and deteriorate, and cracking due to age.
Ball joints have a metal ball that locates into a nylon socket and it is the wear in the nylon socket that results in the excess movement. Some ball joints are fitted with grease nipples and can be routinely lubricated, however most modern ball joints are sealed for life and no maintenance is needed.
If worn bushes and ball joints are not replaced then the driver may experience vague steering and the steering geometry will be compromised which will lead to uneven and premature tyre wear.