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8/3/2019 Rear Suspension System Design
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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
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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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8/3/2019 Rear Suspension System Design
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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
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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.
11-001
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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.
11-002
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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.
11-003
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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.
11-004
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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.
11-005
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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.
11-006
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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.
11-007
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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.
11-008
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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.)
11-009
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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.
11-010
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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.
11-011
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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.
11-012
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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.
11-013
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