Rear Suspension System Design

8/3/2019 Rear Suspension System Design

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U N I T E L EV E NU N I T E L EV E N

R E A R S U S P E N S I ON S Y S T E MR E A R S U S P E N S I ON S Y S T E M

D E S I G N A N D R E P A I RD E S I G N A N D R E P A I R

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TABLE OF CONTENTSTABLE OF CONTENTS

LESSON ONE - REAR SUSPENSION SYSTEM DESIGN ...........................................................2

NON-INDEPENDENT REAR SUSPENSIONS ..... ...... ..... ...... ...... ..... ...... ..... ...... ...... ..... ...... ..... .3

Solid Rear Axle Suspension - Rear-Wheel Drive ...... ...... ..... ...... ..... ...... ...... ..... ...... ..... ..... .....3

Solid Rear Axle Suspension - Front-Wheel Drive..................................................................5

SEMI-INDEPENDENT REAR SUSPENSIONS ..... ...... ..... ..... ...... ..... ...... ..... ...... ...... ..... ...... ..... .6

Trailing Arm Suspension............................................................................. .......................6

Trailing Arm with Track Bar.................................... ....................................................... .....7

Torsion Bar Rear Suspension.............................................................................................8

INDEPENDENT REAR SUSPENSIONS (REAR-WHEEL DRIVE)..............................................9

Short Long Arm (SLA) Rear Suspension ...... ..... ...... ...... ..... ...... ..... ...... ...... ..... ...... ..... ..... .....9

Rear Trailing Arm Suspension..................................................................... .....................10INDEPENDENT REAR SUSPENSIONS (FRONT-WHEEL DRIVE) ......... ......... ......... ......... ..11

Short Long Arm (SLA) Rear Suspension ...... ..... ...... ...... ..... ...... ..... ...... ...... ..... ...... ..... ..... ...11

MULTI-LINK REAR SUSPENSIONS.....................................................................................13

Chapman Strut ..................................................... ....................................................... ...13

Multi-Link Rear Suspension ..................................................... ........................................ 14

Modified Strut Rear Suspension ............................................... ........................................ 15

Wishbone Rear Suspension.......................................................................................... ...16

LESSON TWO - REAR SUSPENSION SYSTEM DIAGNOSIS AND SERVICE ...........................18

SHOCK ABSORBERS ...................................................... ................................................. 19

COIL SPRINGS............................................................................................. .....................19

STABALIZER BARS AND BUSHINGS ..... ...... ..... ...... ..... ..... ...... ..... ...... ..... ...... ...... ..... ...... .... 20

STABALIZER BAR ATTACHING LINKS................................................................................20

KNUCKLES.......................................................................................................................20UPPER CONTROL ARMS ................................................. ................................................. 20

UPPER BALL JOINT WEAR INSPECTION...........................................................................21

LATERAL LINKS................................... ........................................................ .....................21

TRAILING LINKS............................................ ........................................................ ............22

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LESSON ONELESSON ONE

REAR SUSPENSION SYSTEMREAR SUSPENSION SYSTEM

DESIGNDESIGN

TERMINAL OBJECTIVESuccessful completion of this Units enabling objectives

(technical competencies) will allow you to meet the

Integrated Curriculum Standards (ICS) listed in the rightmargin.

ENABLING OBJECTIVESUpon completion of Lesson One, you should be able to:

Identify and explain the basic characteristics ofleaf, control arm, and strut-type rear suspensionsystems.

Explain the function of springs and Hookes law.

Explain the terms force, inertia, lever, andmomentum, and how these science terms apply toautomotive steering and suspension systems.

ICS

045

Problem Solving and

Decision

155

Steering and

Suspension Systems

166

Inspection

167

Diagnosis

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NON-INDEPENDENT REAR SUSPENSIONSSolid Rear Axle Suspension - Rear-Wheel Drive

Many rear wheel drive vehicles use solid axles for the rear

suspension because the ring, pinion and axles can all be contained

in one axle or housing. They are also durable and economical.

Solid axles can be supported with leaf or coil type springs. The first

configuration, using leaf springs, controls fore/aft, lateral, braking and

acceleration forces because the main leaf attaches the axle to the

frame.

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When coil springs are used, control arms are also used. Control

arms are arranged to hold the axle in proper position. There arethree basic arm configurations. The trailing arm configuration uses

four arms and is often called a "four link" or "quad link" system.

These suspensions were designed to improve rear tire traction in

high horsepower applications by tuning the link's pivot points to

intersect the vehicle's center of gravity or front to rear roll axis. This

improved the leverage created by the axle torque to transfer vehicle

weight under acceleration to the rear tires. A track bar is sometimes

used, depending on upper control arm configuration.

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Solid Rear Axle Suspension - Front-Wheel DriveMany front-wheel drive vehicles also use a solid rear axle. Since

there are no rear driveline components, all that is needed is a section

of box or round steel tubing. Usually solid rear axles are mounted

with leaf springs to control the various forces. Once again, the

advantages of this system are the low cost and high durability.

Some front-wheel drive vehicles use a "V"- shaped solid axle that

permits a small amount of deflection, providing some independent

action.

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SEMI-INDEPENDENT REAR SUSPENSIONSTrailing Arm Suspension

The system is similar to a MacPherson strut suspension, but the

control arms are mounted in the rear and are called trailing arms.

The spindles are mounted on the rear of the trailing arms. A coil

spring is mounted on the shock absorber. The shock absorber

assembly, which is mounted to the trailing arm and upper spring

seat, supports the vehicle and cushions road variations.

The trailing arms are connected by a lateral beam (crossmember),

which can flex or deflect during body roll and hard turns. The

deflection is proportional to the load and permits a limited amount of

independent movement.

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Trailing Arm with Track Bar

Trailing arm rear suspensions typically use a "U"-channel axle beam

welded to one end of the trailing arms. The spindles bolt to the ends

of the axle beam. Shock absorbers and coil springs are mounted on

the axle by the trailing arms. Rear suspensions with trailing arms

must have a means to control lateral axle movement, so a track bar is

attached to the axle beam and frame. Additional control arms,

mounted diagonally to control lateral axle movements, can also be

used.

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Torsion Bar Rear SuspensionA rear transverse torsion bar suspension is shown below. It

operates similar to the front transverse torsion bar suspension. In

this suspension the torsion bars are mounted in a line block located

in the center of the vehicle. The outer ends are mounted into the

trailing arms, which support the vehicle. The trailing arms are

attached to the vehicle at the torsion support brackets. In this

system, there are two torsion bars; one for the left side and one for

the right side. This is because during suspension movement the

torque is exerted on the torsion bars at different angles.

The bar directly behind the torsion bars is an anti-roll (anti-sway or

stabilizer) bar. It transfers vehicle weight from the outside to the

inside as the vehicle turns. It is important to follow the Service

Manual procedures when servicing the rear suspension on these

vehicles. Special tools are necessary for obtaining proper vehiclecurb height. The anti-roll bars must be installed prior to the torsion

bars.

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INDEPENDENT REAR SUSPENSIONS(REAR-WHEEL DRIVE)

Short Long Arm (SLA) Rear Suspension

A SLA configuration is sometimes used on the rear suspension.

This rear SLA suspension uses two half-shafts with universal joints.

This suspension is also referred to as a "toe link" suspension,

because of its rear steering capabilities designed into it.

Some rear suspensions use upper and lower control arms that are

high-strength tubular steel. The arms have ball joints, which are

replaceable and support the rear knuckle. The knuckle rotates,

providing passive rear steering. The knuckle is much like a front-

wheel drive vehicle's knuckle, because it has a hub and bearing

assembly. A half-shaft (driven by the rear differential) drives the rear

wheel and is supported by the hub and bearing assembly. This SLA

suspension provides a knuckle (axis) for rear steering to occur. This

system is compact and provides the strength required.

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Rear Trailing Arm SuspensionOn rear-wheel drive applications, a transverse leaf spring or coil-over

shocks can be used to provide vehicle support with the differential

attached to the frame or driveline. The control arms may be trailing

or front to rear links may be used. A lateral link or arm must also be

used to control the wheel's vertical position and side forces.

This suspension is independent because it allows each rear wheel to

be driven by a separate half-shaft (axle), which can move

independently from the opposite half-shaft. The half-shafts use

constant velocity or universal joints to allow independent up-and-

down movement, like many front-wheel drive suspensions.

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INDEPENDENT REAR SUSPENSIONS (FRONT-WHEEL DRIVE)

Short Long Arm (SLA) Rear Suspension

A fully independent SLA rear suspension is used on some vehicles.

In this configuration, the U-shaped upper control arm is attached to

the knuckle through a ball joint and to the rear crossmember with a

pivot pin. Two lateral arms replace the traditional one-piece lower

control arm. Each lateral arm is attached at one end to the knuckle(one at the front and one at the rear) and to the rear crossmember at

the other end. The lateral arms control lateral movement of the

knuckle.

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A trailing arm, attached between the knuckle and a bracket on the

vehicle's underbody, is used to control fore and aft movement of theknuckle. A stabilizer bar is used to control forces encountered

during turning. The stabilizer bar is attached to each forward lateral

arm through stabilizer bar links and to the rear crossmember. Coil-

over shock absorbers are attached between the knuckle and the

vehicle's underbody. (The coil springs are rated separately for each

side of the vehicle.)

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MULTI-LINK REAR SUSPENSIONSChapman Strut

Independent rear suspensions are often seen on front-wheel drive

vehicles. This is because rear-wheel drive transmission and

driveline components are not needed and the wheels can be

mounted on short (stub) axles. The spindle is sometimes mounted

on a Chapman strut. When Chapman struts are used, lateral links

are attached to the front and rear of the spindle and to the rear

crossmember to control lateral movement. A trailing arm is used to

control fore and aft spindle movement.

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Multi-Link Rear SuspensionThe multi-link rear suspension system is similar to the multi-link front

system. Upper and lower lateral arms attach between the knuckle

and rear crossmember, and are used to control lateral forces. The

compression arm found on the front system is replaced with a toe

control arm, which also connects between the crossmember and

knuckle. Also, a trailing arm is added to control fore and aft forces.

A coil-over shock absorber attaches between the vehicle's body and

the knuckle.

The toe control arm limits toe-out on turns tendencies, and helps to

control toe angles during cornering. The configuration of the lower

lateral arm and toe control arms also provide passive rear steering.

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Modified Strut Rear SuspensionOn rear modified strut applications, the coil spring mounts on the

control arm and frame. The control arm contains a strut (rod) to

prevent fore and aft movement or is an A-shaped arm. The

assembly is a strut without a pivot or spring like the Chapman strut.

The modified rear strut suspension is independent and can have

slight camber changes during turns. It uses more components than

a straight axle. The modified strut also allows for more passenger or

luggage compartment room in some applications because the coil

spring is mounted lower in the vehicle.

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Wishbone Rear SuspensionThe wishbone suspension system is similar to SLA systems and is

also fully independent. In this design, the knuckle and trailing arm

are one piece. The trailing arm portion of the knuckle controls fore

and aft movement and is attached to a bracket on the vehicle's

underbody. The knuckle is also attached to the upper and lower

control arms and assist link. The assist link and lower control arm

attach to the bottom of the knuckle and the upper control arm

attaches to the top of the knuckle. The opposite ends of these three

arms are attached to the rear crossmember. All three are used to

control lateral forces.

A coil-over shock absorber mounts between the knuckle and the

vehicle's underbody. A stabilizer bar, connected to the knuckles at

each end through stabilizer bar links and to the rear crossmember at

the center, controls suspension movement during turns and

acceleration.

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The advantages that the wishbone suspension system offers are

good high-speed cornering and directional stability. This suspensionsystem is lightweight and space efficient, and is most often used on

high performance cars.

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Rear Suspension System Design