Suspension Systems

Suspension fundamental principles	Principles of suspension	Sprung mass refers to vehicle parts supported on the springs, such as the body, frame, and engine. Unsprung mass includes parts of the steering and suspension not supported by springs, such as wheels, tires, and brake assemblies.
	Suspension force	Leaf springs absorb applied force by flattening out under load. Coil springs absorb force of impact by twisting. Torsion bars twist around their center.
	Unsprung weight	Parts of a vehicle not supported by the suspension system are known as unsprung weight.
	Wheel unit location	Driving thrust, braking torque, and cornering force operate to displace wheel units. These forces must be transferred to the vehicle frame, but the wheel units must stay aligned with each other, and with the frame.
	Dampening	Dampening prevents or reduces the bouncing effect of oscillation by absorbing the energy from the oscillation.

Types of suspension	Suspension systems	The purpose of the suspension system is to isolate the vehicle body from road bumps and vibrations, while keeping the wheels in contact with the road.
	Solid axle	The solid, or beam, axle is used in the rear suspension of many front-engined, rear-wheel drive cars, and light commercial vehicles, and as the front suspension on many heavy commercial vehicles.
	Dead axle	A dead axle only supports the vehicle and doesn't transmit any drive. With a live axle, the drive is transmitted through the final drive unit and axles to the wheels.
	Independent suspension	Independent suspension helps keep unsprung mass low. Also, if a wheel hits an irregularity, it won't upset the opposite wheel on the same axle. It allows wheel camber to be adjusted, or designed into the suspension geometry.
	Rear independent suspension	For independent suspension on the rear of a vehicle, many front-wheel drive cars use a McPherson strut at the rear. On rear-wheel drive vehicles, the suspension has to allow for the external drive shafts.
	Rear-wheel drive independent suspension	On rear-wheel drive vehicles with independent suspension, the final drive unit is fixed to the vehicle frame. Drive is transmitted to each wheel by external drive shafts.
	Adaptive air suspension	Adaptive air suspension is an electronically controlled air suspension system at all four wheels with a continuously adaptive damping system.
	Adaptive air suspension operation	The height sensor uses the induction principle to constantly monitor the distance between the vehicle's axle and its chassis.

Types of springs	Coil springs	The load-carrying ability of a coil spring depends on the wire diameter, the overall spring diameter, its shape, and the spacing of the coils. Coil springs can look alike but give very different load ratings, which are often color coded for identification.
	Leaf springs	A leaf spring locates the axle housing longitudinally and laterally. It sustains torque reaction on acceleration, and braking torque on deceleration. Driving thrust transfers through the front half of the spring to the fixed shackle point.
	Torsion bars	A torsion bar is fixed to the chassis or sub-frame at one end, and the suspension control arm at the other. Deflection of the suspension causes the bar to twist around its center, to provide the springing action.
	Rubber springs	Increasing the load on a suspension causes the rubber cone to act like a spring being deformed. When the load is removed, the rubber's elastic properties tend to return it to its original state.

Shock absorber types	Hydraulic shock absorbers	The dampening action of a hydraulic shock absorber comes from transferring oil, under pressure, through valves that restrict the oil flow. Resistance to motion is low when the piston moves slowly, and high when its velocity is high.
	Gas-pressurized shock absorbers	Shock absorber 'dissolve' can be reduced by pressurising the fluid with nitrogen.
	Load-adjustable shock absorbers	The rubber air cylinder in the load-adjustable shock absorber can be pressurized to assist suspension springs that are under load. Changing the pressure in the cylinder can alter ride height, and the stiffness of the suspension.
	Manual adjustable-rate shock absorbers	In a manual adjustable-rate shock absorber, the position of the valves in the piston can be changed, to vary the number of restrictions the oil has to pass through, and to vary the force needed to open the valves.
	Electronic adjustable-rate shock absorbers	The electronic adjustable-rate shock absorber has a rotary solenoid that can alter dampening rate by changing the number of restrictions the oil must pass through, and varying the force needed to open the valves.
	Automatic load-adjustable shock absorbers	Automatic load-adjustable shock absorbers maintain vehicle ride at a pre-set level, according to the load placed over the rear axle.

Front suspension types & components	Strut suspension	In strut suspension a telescopic type shock absorber is contained inside the strut with the coil spring mounted over the strut inside the suspension tower. The control arm mount is fixed (or 'held in place') in the vehicle configuration, by bushes.
	Short/long arm suspension	In short/long arm suspension the lower control arm pivots on bushes that twist on the lower control arm pin, which is bolted to the cross-member of the vehicle. The lower control arm is longer than the upper control arm.
	Torsion bar suspension	The torsion bar supports the vehicle load and twists around its center to provide the springing action. The spring rate depends upon the length of the bar. The shorter and thicker the bar, the stiffer its spring rate.

Rear suspension types & components	Rigid axle leaf spring suspension	The leaf spring is usually made up of a number of leaves of different length. The top, or longest leaf, is normally referred to as the main leaf.
	Rigid axle coil spring suspension	The telescopic-type shock absorber is attached to the axle at the bottom and to the chassis at the top. The coil spring is mounted between the axle housing and the vehicle body.
	Independent type suspension	The trailing arm is attached to the chassis at a rigid cross-member pivot point. This pivot point is fitted with rubber bushes. The fixing frame is attached to the vehicle body. The frame supports the differential unit and its housing.
	Rigid non-drive suspension	This type of suspension is known as a 'Dead Axle'. It does not transmit any drive. The panhard rods function is to assist in stabilizing the vehicle from lateral movements.

Suspension system layouts	Driven rear suspension layouts	There are several different driven or 'live' axle rear suspension system layouts.
	Non-driven rear suspension layouts	There are several different non-driven or 'dead' rear suspension system layouts.
	Independent rear suspension layouts	There are several different layouts that use independent driven or 'live' axle rear suspension systems.
	Front suspension layouts	Front suspension layouts can use 'live' or 'dead' axle systems.
	Bushes/bushings	Bushes, or bushings, act as bearings at suspension fulcrum points, to allow for movement of the component, while maintaining its alignment.
	Arms & linkages	A pan-hard rod can restrict lateral movement of the rear axle during cornering. Bushes or mountings at each end locate it on the axle and frame.

Suspension system procedures	Checking shock absorbers	Shock absorbers and struts are located near each wheel and protect the passenger compartment from bumps. Many of today's vehicles are equipped with strut type suspension instead of conventional shock absorbers, but testing either system involves the same procedure. The objective of this procedure is to show you how to check the serviceability of the shock absorbers and struts.
	Changing shock absorbers	Shock absorbers are also known as dampers. Their task is to reduce suspension oscillations. The two most common types are strut cartridges and telescopic shock absorbers. Each type has a different shock absorber replacement procedure. The objective of this procedure is to show you how to safely replace shock absorbers.
	Lubricating a suspension system	Many older vehicles on the road had numerous lubrication points. Today's vehicles have far fewer, if any, points that need lubricating. The objective of this procedure is to show you how to lubricate suspension and steering components to the manufacturer's specifications.
	Servicing a suspension system	The components of the vehicles suspension system are designed to operate as a whole unit. Some vehicles use very sophisticated systems, while others use very simple systems. The objective of this procedure is to show you how to check front and rear suspension components and measure their wear.

Topic group	Topic	Summary