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Learning Objective: Automotive front suspension

  • Suspension
  • Fundamental suspension parts
  • Suspension types
  • Ball joint types / purposes
  • Struts
  • Shock absorbers
  • Suspension spring types

After finishing this chapter, you should be familiar with these fundamental learning objectives:

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SUSPENSION PRINCIPLES

  • Suspensions use various links, arms, and joints to allow the wheels to move freely up and down; front suspensions also have to allow the front wheels to turn.
  • All suspensions must provide for the following supports:
    • Transverse (or side-to-side) wheel support
    • Longitudinal (front-to-back) wheel support

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TYPES OF SUSPENSIONS

  • Early suspension systems used a solid axle for front and rear wheels.
    • If one wheel hit a bump, the other wheel was affected.

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Solid I-beam axle with leaf springs.

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TYPES OF SUSPENSIONS

A typical independent front suspension used on a rear-wheel-drive vehicle. Each wheel can hit a bump or hole in the road independently without affecting the opposite wheel.

Most vehicles today use a separate control-arm-type of suspension for each front wheel, which allows for movement of one front wheel without affecting the other front wheel.

This type of front suspension is called independent suspension.

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SHORT - LONG ARM (SLA)

  • Short / Long Arm
    • The lower control arm is longer than the upper control arm
  • SLA 2
    • Suspension spring is mounted on the upper control arm

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MacPHERSON STRUT

  • MacPherson Strut
    • Incorporates shock, spring, and strut body. Replaces upper control arm
  • Modified Strut
    • Spring is separate – mounts between lower control arm and frame

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TWIN I-BEAM SUSPENSION

  • Improved version of single I-beam suspension
  • Steering knuckles are attached using king pins

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SUSPENSION PARTS�CONTROL ARMS

  • A control arm is a suspension link that connects a knuckle or wheel flange to the frame.
  • One end of a control arm attaches to the knuckle or wheel flange, generally with either a ball joint or bushing.
  • The opposite end of the arm, which attaches to a frame member, usually pivots on a bushing.

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SUSPENSION PARTS�CONTROL ARMS

Control arms are used to connect the steering knuckle to the frame or body of the vehicle and provide the structural support for the suspension system.

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SUSPENSION PARTS�STEERING KNUCKLES

  • A steering knuckle is hard to classify either as part of the suspension or as part of the wheel.
  • A knuckle serves two purposes:
    • To join the suspension to the wheel
    • Usually includes the spindle where the front wheel bearings are attached
    • To provide pivot points between the suspension and wheel.

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SUSPENSION PARTS�STEERING KNUCKLES

The steering knuckle used on a short/long-arm front suspension.

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SUSPENSION PARTS�STEERING KNUCKLES

FIGURE 6–32 A kingpin is a steel shaft or pin that joins the steering knuckle to the suspension and allows the steering knuckle to pivot.

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SUSPENSION PARTS�THE SPINDLE

The spindle supports the wheels and attaches to the control arm with ball-and-socket joints called ball joints. The control arm attaches to the frame of the vehicle through rubber bushings to help isolate noise and vibration between the road and the body.

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SUSPENSION PARTS�BALL JOINTS

  • Ball joints are ball-and-socket joints, similar to the joints in a person’s shoulder.
  • Ball joints allow the front wheels to move up and down, as well as side to side (for steering).

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BALL JOINTS�BALL JOINT DESIGN

  • There are two basic designs of ball joints: compression loaded and tension loaded.
  • If the control arm rests on the steering knuckle, the ball joint is compressed into the control arm by the weight of the vehicle.
  • If the knuckle rests on the control arm, the weight of the vehicle tends to pull the ball joint back into the control arm by tension.
  • All ball joints, whether tension or compression loaded, have a bearing surface between the ball stud and socket

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SUSPENSION PARTS: BALL JOINTS

The lower ball joint is load carrying in this type of suspension because the weight of the vehicle is applied through the spring, lower control arm, and ball joint to the wheel.

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SUSPENSION PARTS�BALL JOINTS

The upper ball joint is load carrying in this type of suspension because the weight of the vehicle is applied through the spring, upper control arm, and ball joint to the wheel. The lower control arm is a lateral link, and the lower ball joint is called a follower ball joint.

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SUSPENSION PARTS�Non-Load-Carrying Ball Joints

Stabilizing / Follower ball joints:

  • Maintain steering knuckle position
  • Does not support vehicle weight
  • Uses internal spring to provide preload

Low Friction ball joints

  • Highly polished
  • High-strength polymer bearing

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SUSPENSION PARTS�STABILIZER BARS

  • Most cars and trucks are equipped with a stabilizer bar on the front suspension, which is a round, hardened steel bar attached to both lower control arms with bolts and rubber bushing washers called stabilizer bar bushings.

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SUSPENSION PARTS STABILIZER BARS

As the body of the vehicle leans, the stabilizer bar is twisted. The force exerted by the stabilizer bar counteracts the body lean.

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SUSPENSION PARTS �STRUT RODS

  • The purpose of these strut rods is to provide forward/backward support to the control arms.
  • Strut rods are used on vehicles equipped with MacPherson struts and many short/long-arm-type suspensions.

The strut rods provide longitudinal support to the suspension to prevent forward or rearward movement of the control arms.

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SUSPENSION PARTS�STRUT RODS

Struts rods are only used when there is only one lower control arm bushing and not used where there are two lower control arm bushings.

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4 BAR AXLE

  • Eliminates side to side travel
  • Helps keep axle perpendicular with the road.

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Review

What is the difference between an SLA suspension and a MacPherson Strut suspension?

To what are the control arm(s) connected?

To what is the spindle connected?

What is the difference between a loaded ball joint and a follower ball joint?

What is the purpose of a stabilizer bar?

What type of control arm requires a strut bar?

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SUSPENSION PARTS�SPRINGS

  • A suspension spring serves two purposes.
    • 1. Acts as a buffer between the suspension and frame to absorb vertical wheel and suspension movement without passing it on to the frame.
    • 2. Each spring transfers part of the vehicle weight to the suspension component it rests on, which transfers it to the wheels.

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SUSPENSION PARTS�COIL SPRINGS

  • The strength and handling characteristics of a coil spring depend on the following:
    • Coil diameter
    • Number of coils
    • Height of spring
    • Diameter of the steel coil that forms the spring.
    • Springs should be checked for bright and shiny spots = weakness

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SUSPENSION PARTS�COIL SPRINGS

This replacement coil spring is coated to prevent rust and corrosion and colored to help identify the spring and/or spring manufacturer.

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SUSPENSION PARTS �COIL SPRINGS

Coil spring ends are shaped to fit the needs of a variety of suspension designs.

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SUSPENSION PARTS�COIL SPRINGS

A constant-rate spring compresses at the same rate regardless of the amount of weight that is applied

Variable-rate springs come in a variety of shapes and compress more slowly as weight is applied.

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Should I Cut My Coil Springs?

  • Chassis service technicians are often asked to lower a vehicle. One method is to remove the coil springs and cut off half or more coils from the spring. While this will lower the vehicle, this method is generally not recommended for the following reasons:
    • A coil spring could be damaged during the cutting-off procedure, especially if a torch is used to do the cutting.
    • The spring will get stiffer when shortened, often resulting in a very harsh ride.
    • The amount the vehicle is lowered is less than the amount cut off from the spring. This is because as the spring is shortened, it becomes stiffer. The stiffer spring will compress less than the original.

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SUSPENSION PARTS �TORSION BARS

  • A torsion bar is a spring that is a long, round, hardened steel bar similar to a coil spring except that it is a straight bar.

A torsion bar resists twisting and is used as a spring on some cars and many four-wheel-drive pickup trucks and sport utility vehicles. The larger the diameter, or the shorter the torsion bar, the stiffer the bar.

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SUSPENSION PARTS �TORSION BARS

  • One end is attached to the lower control arm of a front suspension and the other end to the frame.
  • When the wheels hit a bump, the bar twists and then untwists.

Longitudinal torsion bars attach at the lower control arm at the front and at the frame at the rear of the bar.

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SUSPENSION PARTS �TORSION BARS

  • As with all automotive springs, spring action is controlled by the shock absorbers.
  • Unlike other types of springs, torsion bars may be adjustable for correct ride height.

One end of the torsion bar attaches to the lower control arm and the other to an anchor arm that is adjustable.

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SUSPENSION PARTS �LEAF SPRINGS

  • Easy
  • Cheap
  • Carries loads well

  • Lateral movement
  • Stiff Suspension

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SUSPENSION PARTS �LEAF SPRINGS

  • Leaf springs are constructed of one or more strips of long, narrow spring steel.
  • These metal strips, called leaves, are assembled with plastic or synthetic rubber insulators between the leaves, allowing for freedom of movement during spring operation.

A typical leaf spring used on the rear of a pickup truck showing the plastic insulator between the leaves, which allows the spring to move without creating wear or noise.

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SUSPENSION PARTS �LEAF SPRINGS

All multileaf springs use a center bolt to not only hold the leaves together but also help retain the leaf spring in the center of the spring perch.

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SUSPENSION PARTS �LEAF SPRINGS

When a leaf spring is compressed, the spring flattens and becomes longer. The shackles allow for this lengthening. Rubber bushings are used in the ends of the spring and shackles to help isolate road noise from traveling into the passenger compartment.

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SUSPENSION PARTS �LEAF SPRINGS

Many pickup trucks, vans, and SUVs use auxiliary leaf springs that contact the other leaves when the load is increased.

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LEAF SPRINGS�COMPOSITE LEAF SPRINGS

  • Since the early 1980s, fiberglass-reinforced epoxy plastic composite leaf springs have been used on production vehicles.
  • They save weight: An 8-pound spring can replace a conventional 40-pound steel leaf spring.

A fiberglass spring is composed of long fibers locked together in an epoxy (resin) matrix.