Suspension%20Systems

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Chapter 45

• Suspension Systems

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Frames

• 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

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Springs

• 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.

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Spring Types (contd)
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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.

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Gas-Filled Shock
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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.

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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.

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Strut Rods

• Found on models that do not have a double pivot
  lower control arm.
• Greatly affected by braking forces and road
  shocks.

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Bushings

• 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.

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MacPherson Strut Suspensions

• Spring
• Shock absorber
• Upper suspension locator and steering pivot

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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

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Typical SLA Suspension
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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 tires
  contact with the road remains constant.

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SLA Suspension Components

• Wheel spindle and steering knuckle
• Upper and lower control arms
• Can be wishbone or double pivot
• Ball joints
• Shock absorber
• Spring

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Ball Joints

• Connects the steering knuckle to the control
  arms.
• Are either load carrying or are followers
• Load carrying joints support the vehicles weight
• Following or friction joints a steering pivot

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Four-Link Front Suspension

• This style optimizes ride quality and movement.
• The influence of drive forces on the steering is
  minimal.

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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.

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Signs of Shock Failure

• More difficult steering and handling.
• Rough braking.
• Excessive bouncing after stops.
• Unusual tire wear patterns.
• Bottoming out springs.

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Chassis Height Specifications

• Inspect for sag, damaged or worn bumpers, or
  shiny spring coils.
• Measure height at specific locations.

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Front-SuspensionComponent 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

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Ball Joints

• Check wear indicator if applicable
• Check for wear with a dial indicator
• Most joints should have no slop or play
• Load carrying joint is on same control arm as the
  spring

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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

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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.

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Rear-Suspension Systems

• Three basic types
• Live axle
• Semi-independent
• Independent
• There are various types within the three basic
  types.

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Leaf Spring Rear Suspension
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Coil Spring Rear Suspension
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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.

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Independent FWD Rear Suspension
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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

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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.

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System Components

• Compressor
• Sensors
• Electronic shock absorbers
• Electronic struts
• Control module
• Leveling control

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Adjustable Pneumatic Suspension
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MagneRide

• 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 fluids viscosity

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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.

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