CH45 suspension systems STUDENT VERSION rev

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Chapter 45

Suspension Systems

• Body Over Frame

– The body and all major parts are bolted to the frame

– Design is used on many pickups and SUVs

• Unitized Body

– Tends to be more tightly structured

– Is designed to transmit impact energy

throughout the vehicle

• Carry vehicle weight

• Absorb road shock forces

• Maintain correct ride height

• The amount the compress under load is called spring rate

• Spring compression is called jounce

• Spring extension is called rebound

Spring Types (cont’d)

Shock Absorbers

• Dampen spring movement

• The faster a shock moves, the more

resistance it has to movement

• Typically has more resistance to extension than compression

• Gas charged shocks are effective at limiting fluid foaming

Gas-Filled Shock

Shock Absorber Ratio

• Valves may provide different resistance for

jounce and rebound

• A 50/50 shock is equal for jounce and rebound

• Damping rates depend on piston and orifice

sizes as well as the closing force of the valves

Stabilizer Bars

• Also called a sway bar or antisway bar

• Reduces body roll or lean

• Typically a one-piece U-shaped steel bar

• Held to the control arms or strut with links

• Used on the front and rear suspensions

Strut Rods

• Found on models

that do not have a

double pivot lower

control arm

• Greatly affected by

braking forces and

road shocks

• Used on stabilizer bars, controls arms, radius arms, and strut rods

• Good for pivots, minimizing lubrication

points, and allow for slight misalignments

• Allow movement between components

• Bushing movement produces heat

• Worn bushings allow suspension movement

MacPherson Strut Suspensions

Strut Mounts

• Dampen vibrations

• Secures the strut in position

• Includes a bearing or bushing

• Worn mounts can cause noise, poor handling, and damage to the strut

• Often replaced with the strut

Typical SLA Suspension

Short-Long Arm Suspension

• Each wheel is connected independently to the frame

• The upper arm pivots in a shorter arc

• The top of the wheel moves slightly but tire’s contact with the road remains

constant

SLA Suspension Components

• Wheel spindle and steering knuckle

• Upper and lower control arms:

– Can be wishbone or double pivot

• Ball joints

• Shock absorber

• Spring

Ball Joints

• Connects the steering knuckle to the control arms

• Are either load carrying or are followers:

– Load carrying joints support the vehicle’s

weight

– Following or friction joints a steering pivot

Four-Link Front Suspension

• This style optimizes

ride quality and

movement

• The influence of

drive forces on the

steering is minimal

Shock/Strut Bounce Test

• Push the bumper down two or three times

• The vehicle should oscillate about one and a half times then settle

• Excessive bounce indicates the shocks are worn and need replaced

• Listen for noises while testing

Signs of Shock Failure

• More difficult steering

Chassis Height Specifications

• Inspect for sag, damaged or worn bumpers,

or shiny spring coils

• Measure height at specific locations

Front-Suspension Component Servicing

• Coil Springs

– Require no adjustment

– Weak springs sag and affect ride height

– Can break from overloading

– To replace, support the lower control arm and attach a spring compressor to safely handle the spring

– Most joints should

have no slop or play

• Load carrying joint is

on same control arm

as the spring

Shock Absorbers

• Will gradually wear and change vehicle stability, handling, and rideability

• Common problems are:

– Excessive bouncing after stops or bumps – Tire tread cupping

– Springs are bottoming out

– Worn, loose, or damaged bushings

MacPherson Strut Suspension

• The strut receives a large amount of vertical and horizontal force.

• Check closely for leaks, bent shaft, and poor damping.

• Mark upper pivot and eccentric cam before removing the strut.

• During replacement, check the strut pivot

bearing.

Leaf Spring Rear Suspension

Coil Spring Rear Suspension

Semi-Independent Suspension

• Used on many FWD

models

• Twisting of the axle

allows for

semi-independent movement

• Only remove one shock

and spring at a time

Independent FWD Rear Suspension

Electronically Controlled Suspensions

• Adaptive Suspensions

– Use electronic shocks or variable air springs

– Sensors monitor vehicle height, speed, steering angle, braking force, damping status, and throttle position

– Some systems are automatic while others allow drivers to select modes

– Reduces body roll but does not eliminate it

Types of Electronic Suspensions

• Adaptive Systems

– Typically use electronic shocks with variable valving.

• Load-leveling Systems

– Use air shocks in the rear to compensate for vehicle load.

• Fully Active Systems

– Use hydraulic actuators as both spring and shock

absorber.

Adjustable Pneumatic Suspension

• Regulates fluid flow by a variable magnetic field produced by a coil in the shock.

• Shocks filled with a magneto-rheological fluid.

• Current flow changes the fluid’s viscosity

Active Suspensions

• Refers to those controlled by double-acting hydraulic cylinders call actuators

• Each acts as a variable spring and shock

• Hydraulic pressure varies to adapt to

changing road conditions

• The computer monitors actuator position and load, steering angle, body roll, and

lateral acceleration