Auto Suspension and Steering, 4th Edition Page 98 (98 of 480)

98 Auto Suspension and Steering
Steering arm
Gasket
Spring
Retainer
Bushing
Steering knuckle
Bearing cap and
kingpin
Seal
Tapered roller bearing
Race
Retainer
Kingpin
Seal
Figure 5-29. A solid driving four-wheel drive front axle assembly. Note that the steering knuckle rides on a tapered roller bearing.
(General Motors)
Frame
I-beam axle
Lower spring
seat
Link
Stabilizer bar
Link
I-beam axle
Radius arm
Upper ball
joint
adjuster
Lower spring
seat
Coil
spring
Shock
absorber
Radius arm
bracket
Jounce
bumper
Figure 5-30. A twin I-beam, non-driving front suspension used on one particular pickup truck. (Ford)

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98 Auto Suspension and Steering
Steering arm
Gasket
Spring
Retainer
Bushing
Steering knuckle
Bearing cap and
kingpin
Seal
Tapered roller bearing
Race
Retainer
Kingpin
Seal
Figure 5-29. A solid driving four-wheel drive front axle assembly. Note that the steering knuckle rides on a tapered roller bearing.
(General Motors)
Frame
I-beam axle
Lower spring
seat
Link
Stabilizer bar
Link
I-beam axle
Radius arm
Upper ball
joint
adjuster
Lower spring
seat
Coil
spring
Shock
absorber
Radius arm
bracket
Jounce
bumper
Figure 5-30. A twin I-beam, non-driving front suspension used on one particular pickup truck. (Ford)

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Chapter 5 Front Suspension Systems 97
U-joint
Tie rod tube
Steering damper
Steering arm
Tie rod end
Hub
Disc
brake
Differential
Figure 5-27. A solid driving front axle used on a four-wheel
drive vehicle. (Moog)
Since the operation of the four-wheel drive places
many forward and backward stresses on the suspension
components, other support is needed. Most solid axles
have control arms or strut rods to keep the axle in place.
Twin I-Beam Axle Front Suspensions
Until recently, twin I-beam axle front suspensions
were used on many Ford trucks. This type of front
suspension actually uses two I-beams, one at each wheel.
The inner portion of each I-beam is attached to the frame
on the opposite side of the wheel that it serves. The I-beam
pivots on bushings similar to those used on the control
arms of a conventional suspension. The outer end of the
I-beam is attached to the steering knuckle, usually through
ball joints. Some older systems may have kingpins. The
twin I-beam design results in a strong axle with better han-
dling characteristics than a single solid axle.
The exact design of the twin I-beam front axle varies
between two- and four-wheel drive vehicles. The differ-
ences between each type are covered below.
Non-Driving Twin I-Beam Axle
The typical non-driving twin I-beam axle is shown in
Figure 5-30. Each I-beam is connected at the frame through
a large single bushing. A coil spring is installed between
the top of the I-beam and the frame, and is usually clamped
in place. Twin I-beam assemblies use strut rod assemblies,
usually called radius arms, to eliminate forward and back-
ward movement of the I-beam. A stabilizer bar assembly is
also used to reduce body lean on turns.
Driving Twin I-Beam Axle
A driving twin I-beam axle resembles a non-driving
twin I-beam assembly. The main difference is that the final
drive assembly (ring and pinion, differential gears) is
installed in the left I-beam, Figure 5-31. Power from the
final drive assembly operates axles installed in each I-beam
assembly. U-joints at each steering knuckle transfer power
from the drive axles to the stub axles. The steering
knuckles are similar to those used on solid drive axles.
Locking hubs are also used with some older four-wheel
drive twin I-beam vehicles.
Washer
Body assembly
Cover assembly
Clutch OFF
Snap ring
Knob
Hub
Bush
Axle shaft
Snap ring
“FREE” position “LOCK” position
Clutch ON
Figure 5-28. Cutaway of a four-wheel drive manual locking hub. Note the difference between “free” and “lock” positions. (Suzuki)

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Chapter 5 Front Suspension Systems 99
Ball Joint Loading
The basics of compression and tension ball joint load-
ing were discussed in Chapter 4, Common Suspension
System Components. This section covers the determination
of loaded and follower joints on actual suspension systems.
On any suspension system, the weight of the vehicle passes
from the frame to the wheels through the spring or torsion
bar. The spring position in relation to the control arm or
arms determines which ball joint is the loaded joint and
which ball joint is the follower joint. Ball joint loading on
MacPherson strut suspensions, conventional suspensions,
and solid or twin I-beam suspensions is discussed below.
MacPherson Strut Suspensions
On a MacPherson strut, the top of the strut assembly
is attached to the vehicle body and the bottom is bolted to
the steering knuckle. Vehicle weight passes through the
strut assembly and the upper part of the steering knuckle to
the wheel. Weight transfer through a MacPherson strut
assembly is shown in Figure 5-32. The lower ball joint is
the only ball joint used on the MacPherson strut and is a
follower joint since the load passes through the strut
assembly. The purpose of the MacPherson strut lower ball
joint is simply to keep the bottom of the wheel in place.
The only variation to this rule occurs on vehicles on
which the coil spring is separate from the strut assembly.
On this type of design the spring is installed between the
frame and lower control arm. The lower ball joint is a
load-carrying joint since the vehicle weight passes from the
frame through the spring and lower control arm and into
the ball joint. The ball joint then transfers the weight to the
steering knuckle.
Conventional Suspensions
Spring or torsion bar placement on conventional sus-
pensions varies, and this affects ball joint loading as
detailed below.
Spring/Torsion Bar on Lower Control Arm
When the spring or torsion bar is on the lower control
arm, the vehicle’s weight passes through the spring, the
lower control arm, the lower ball joint, and into the
steering knuckle. See Figure 5-33. Therefore, the lower ball
joint is the load-carrying joint. The upper ball joint keeps
the wheel in position.
Spring/Torsion Bar on Upper Control Arm
When the spring or torsion bar is on the upper control
arm, the vehicle’s weight passes through the spring, the
upper control arm, the upper ball joint, and into the
steering knuckle. See Figure 5-34. Therefore, the upper
ball joint is the load-carrying joint. The lower ball joint
keeps the wheel in position.
Solid and Twin I-Beam Suspensions
On solid or twin I-beam suspensions, the ball joints
are solidly attached to the same beam. Therefore, the
weight is evenly split between each ball joint. There are no
loaded and follower ball joints. In these suspension
systems, the ball joints can be tension or compression
loaded.
U-joint
Drive
axle
Road
bump
Steering
knuckle
I-beam
Differential
assembly
Coil spring
Figure 5-31. A four-wheel drive, twin I-beam suspension. Each
side of the suspension flexes individually when traveling over
bumps. (Perfect Circle)
Vehicle
strut mount
Ball joint
Figure 5-32. Weight transfer through a MacPherson strut
suspension.

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