Chapter 25
Steering and
Alignment
Objectives (1 of 2)
• Identify the components of the steering system of a
heavy-duty truck.
• Describe the procedure for inspecting front axle
components for wear.
• Explain how toe, camber, caster, axle inclination,
turning radius, and axle alignment affect tire wear,
directional stability, and handling.
• Describe the components and operation of a worm
and sector shaft and a recirculating ball-type
steering gear.
• Explain how to check and adjust a manual steering
gear preload and backlash.
Objectives (2 of 2)
• Identify the components of a power steering
gear and pump and explain the operation of a
power steering system.
• Describe the components and operation of a
pneumatic steering system.
• Describe the components and operation of
an electronically variable power steering
system.
• Describe the components and operation of a
load sensing power assist steering system.
• The steering system in a
heavy-duty truck is expected
to:
– Deliver precise directional
control of the chassis at
both gross and unloaded
vehicle weight
– Be able to minimize driver
effort while retaining some
road feel
• Truck steering systems can
be either manual or powerassisted.
• Some hydraulic powerassisted systems are
available with electronic or
load sensing controls.
• Coupled to the steering
column upper shaft by a pair
of yokes and the U-joint
assembly is the lower shaft
assembly.
• The steering column assembly
usually supports some other
switch and control
components. This helps keep
the driver’s hands nearby.
• A multifunction stalk switch,
which contains the turn signal
switch at a minimum, is
usually mounted on the left
side of the steering column.
• If the vehicle is equipped with
a trailer service brake control
valve, it is clamped onto the
right side of the steering
column.
Pitman Arm
• A Pitman arm is a steel lever,
splined to the sector (output)
shaft of the steering gear.
• The end of the Pitman arm
moves through an arc with the
sector shaft center forming its
center.
• The Pitman arm functions to
change the rotary motion of
the steering gear sector shaft
into linear motion.
• The length of the Pitman arm
affects leverage and therefore
steering response.
– A longer Pitman arm will
generate more steering
motion at the front wheels for
a given amount of steering
wheel movement.
Drag Link
• A drag link is a forged rod that
connects the Pitman arm to
the steering control arm.
• The drag link can be a one- or
two-piece component.
• The length of two-piece design
is adjustable, which makes it
easy to center the steering
gear with the wheels straight
ahead.
• The drag link is connected at
each end by ball joints. These
ball joints help isolate the
steering gear and Pitman arm
from axle motion.
Steering Column Arm
• The steering control arm
connects the drag link to
the steering knuckle on the
driver side of the vehicle.
• A steering control arm is
also known as a steering
arm, a control arm, and a
steering lever.
• When the drag link is
moved in a linear direction,
the steering control arm
moves the steering
knuckle, which changes
the angle of the steering
knuckle spindle.
• Steering knuckles mount to
the front axle by kingpins or
knuckle pins.
• Kingpins provide the ability to
steer the vehicle.
• Spindle
– The steering knuckle
incorporates the spindle onto
which wheel bearings and
wheel hubs are mounted, plus
a flange to which the brake
spider is bolted.
• A steering control arm is
attached to the left side
steering knuckle.
• Ackerman arms are attached
to both steering knuckles.
King Pins
• Tapered
– Drawn into the axle center and
secured by tightening a nut at
the upper pin end
– Usually sealed and may not
require periodic lubricating
• Straight
– Secured to the axle with
tapered draw keys that bear
against flats on the pin
– Have a cap on either end (top
and bottom) to retain grease.
– Zerk-type grease fittings are
used to lubricate steering
knuckles.
• Lubed for life
– On newly introduced unitized
steer axles, the steering
knuckle is lubed-for-life; no
attempt should be made to
lubricate these.
Ackerman Arm
• An Ackerman or tie-rod arm is the means used to
transfer and synchronize steering action on both
steer wheels on a steering axle.
• Ackerman arms are drop-forged, tempered steel
levers that are angled to define the steering
geometry required on turns.
• One end of an Ackerman arm is keyed and bolted
to the lower portion of the steering knuckle.
• The other end is taper bored to allow a tie-rod ball
stud to be clamped to it.
Front-end Alignment (1 of 2)
• A front end that is properly aligned will result
in:
– Easier steering
– Longer tire life
– Directional stability
– Less wear on front-end components
– Better fuel economy
– Increased safety
Front-end Alignment (2 of 2)
• The primary alignment angles are:
– Toe
– Caster
– Camber
– Kingpin inclination
– Turning angle
Toe (1 of 2)
• The ideal toe angle when a vehicle is running
loaded down a highway is zero.
• We set toe angles statically.
– The objective of setting toe at a specified angle when
aligning the front end is to have zero toe at highway
speeds.
Toe (2 of 2)
• Incorrect toe angles not only accelerate tire wear but also can
have an adverse effect on directional stability of the vehicle.
• Incorrect toe angles have the potential to cause more front tire
wear than any other incorrect alignment angle.
• Too much toe-in produces a scuffing, or a featheredge, along the
inner edges of the tires.
• Excessive toe-out produces a similar wear pattern along the
outer edge of the tires.
• When a fully loaded vehicle is moving at highway speeds, there
is a slight tendency of steering tires to toe-out.
• Any looseness in the steering linkage and tie-rod assembly also
will contribute to the toe-out tendency.
Camber
• Steering tires also are designed to use a positive
camber angle setting.
• We will take a closer look at camber later but,
because it influences the toe setting, we will define
it here.
• Camber is a measure of the angle a wheel leans
away or toward the frame.
– Positive camber means that the tires lean away from
the truck frame at the top.
– A positive camber setting is used to help compensate
for that slight tendency of steering tires to toe-out
when the vehicle is moving.
Measuring Toe (1 of 2)
• First check kingpin inclination,
camber, and caster. Correct, if
necessary.
• You should not make an
adjustment to toe angle until
the other factors of frontwheel alignment are known to
be within specifications.
• Adjustment of toe angle or
dimension requires
lengthening or shortening the
tie-rod dimension.
– This is achieved by
loosening the tie-rod end
clamp bolts and then rotating
the cross tube.
Measuring Toe (2 of 2)
• Neutralize the suspension first.
– When measuring toe angle, the front suspension
should be neutralized:
• To neutralize the suspension, roll the vehicle back and
forth about a half vehicle length. This relaxes the front
suspension and steering linkages.
• Neutralizing the front suspension is important before
making front-end adjustments, especially if the vehicle
has been jacked up on either side to scribe the tires.
• This operation causes the front wheels to angle as each
is returned to the floor.
• Make sure that the wheels are on the ground and
fully supporting the vehicle weight. Measure and
record the measurements.
Shop Talk
• When tie-rod ends are replaced, they must
be threaded into the tie-rod cross tube
sufficiently so that clamp pressure is applied
directly over the threads under the clamp.
The threaded end should extend past the slot
in the cross tube.
• CAUTION: Recheck the toe setting after any
change in caster or camber angle.
Deep Drop Tie-Rod Ends
• Toe-in tends to increase
slightly on some steer axles
when loaded and stationary.
• It is therefore important that
vehicles with set-back axles
and deep drop tie-rod ends
are given some special
attention.
• Because of the turning
geometry that results from setback and deep drop tie-rod
end axles, the tie-rod end
clamps if facing forward can
interfere with the axle I-beam
on a full lock turn.
– This interference will not
necessarily impede steering
control, but it can reduce the
effective turn angle of the
vehicle.
Caster (1 of 2)
Caster (2 of 2)
• Caster is the forward or rearward tilt of the kingpin
centerline when viewed from the side of the vehicle.
• Zero caster occurs when the centerline of the
kingpin is exactly vertical.
• Positive caster indicates the kingpin is tilted
rearward.
• Negative caster indicates that the kingpin is tilted
forward.
• Caster is a directional stability angle only. Incorrect
caster by itself will not affect tire wear.
• Most heavy-duty trucks are designed with some
degree of positive caster.
Positive Caster
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Positive caster creates a force in the front wheels, which tends to keep
them tracking straight ahead.
Positive caster tends to make the steering axle wheels want to return to
a straight ahead position.
Positive caster also means that when the front wheels of the truck are
turned, one side of the vehicle raises slightly and the other side is
lowered.
When the steering wheel is released, the weight of the vehicle forces the
lifted side downward, resulting in the wheels returning to a straightahead position.
Caster settings generally affect steering performance in the following
ways:
– Too little caster can cause wheel instability, wandering, and poor wheel
recovery.
– Too much caster can result in hard steering, darting, oversteer, and low
speed shimmy.
Caster Recommendations
• Examples are measured
weight down on a level floor:
– Tandem drive axle: ½–1½
degrees positive
– Single drive: 1½–2 ½ degrees
positive
– No more than 1/2 degree
difference between the left
and right wheels
– Positive caster on the left
wheel should not be greater
than on the right.
• Caster specifications are
based on vehicle design load
which will usually result in a
level frame.
• If the frame is not level when
alignment checks are made,
this must be factored in the
caster measurement.
Twisted Axles
• In a few cases, steering problems can be traced to
a twist in the front axle. A twisted steer axle can be
caused by an actual structural twist, or one induced
by improper use of caster shims.
• A twisted axle should be suspected whenever:
– The difference in caster angle exceeds 1/2 degree
from side to side
– The caster shims in place differ by 1 degree or more
– A low speed shimmy exists, and there is no evidence
of looseness elsewhere in the steering system
– A leading or darting condition persists
Camber
• Excessive positive camber
causes the tire to wear on
its outside shoulder.
• Excessive negative camber
causes the tire to wear on
its inside shoulder.
• Unequal camber in the front
wheels also can cause the
steering to lead to the right
or left.
• The truck will lead to the
side that has the most
positive camber.
Kingpin Inclination (KPI)
• The amount that the top of the
kingpin inclines away from
vertical as viewed from the
front of the truck
• In conjunction with camber
angle, places the approximate
center of the tire tread
footprint in contact with the
road
• Reduces steering effort and
improves the directional
stability
• Cannot be adjusted in trucks
– Once set, KPI should not
change unless the front axle
has been bent.
• Corrections or changes
accomplished by replacement
of broken, bent, or worn parts
Turning Angle or Radius
• Turning angle or radius is the
degree of movement from
straight-ahead to either an
extreme right or left position.
• Two factors limit the turning
angle.
– Tire interference with the
chassis and steering gear
travel
• To avoid tire interference or
bottoming of the steering gear,
there are adjustable stop
screws on the steering
knuckles
• Turning radius or angle should
be checked using the radius
gauge.
Shop Talk
• The power steering gear pressure relief valve
should open just before the steering stop
screw contacts the axle stop.
• You may have to adjust the power steering
gear so that power-assist stops
approximately 1 degree before the steering
stops contact.
– Failure to do this will result in slamming of the
steering stops on full lock turns.
Ackerman Geometry (1 of 2)
• Ackerman geometry is the means used to steer a vehicle so
that the tires track freely during a turn.
• During a turn, the inboard wheel on a steer axle has to track a
tighter circle than the outer wheel.
• Ackerman geometry is also known as toe-out during turns. It
allows the inner and outer wheel to turn at different angles so
that both wheels can negotiate the turn without scrubbing.
Ackerman Geometry (2 of 2)
• Toe-out on turns is
accomplished by having the
ends of lower steering arms
(those that connect to the tierods) closer together than the
kingpins.
• Actual toe-out during a turn
depends on the length and
angle of the steering control
arms and the length of the
cross tube.
• Even if the toe-in setting with
the wheels in a straight-ahead
position is correctly adjusted,
a bent steering arm can cause
the toe-out on a turn to be
incorrect, causing tire scuffing.
Axle Alignment (1 of 2)
• All of the axles should be
perpendicular to the vehicle’s
centerline.
• The thrustline thus created is
parallel to the vehicle
centerline.
• If they are not positioned
perpendicular to the vehicle
centerline, the rear wheels will
not track directly behind the
front wheels, and the thrustline
of the rear wheels deviates
from the centerline of the
vehicle.
• The steering fights the vehicle
thrustline, resulting in an uncentered steering wheel and
accelerated front tire wear.
Axle Alignment (2 of 2)
• On a single-axle vehicle, the
rear-axle thrustline can be off
if the entire axle is offset or if
only one wheel has an
improper toe angle.
• On a tandem axle, there are a
number of different
combinations that can cause
incorrect tracking.
• One method of checking a
single axle for misalignment is
to clamp a straightedge across
the frame so that it is square
with the frame rails.
• Measure from the center of
the hub to the straightedge.
• The distances on each side
should be within 1/8 inch of
each other.
Trailer Tracking
• It is also possible for the trailer
axles to be out of alignment
and cause a tracking problem.
• Depending on the severity of
the trailer misalignment, it
might be possible to see the
effects of the misalignment as
the trailer travels down the
road.
• Usually, the trailer will travel at
an angle to the tractor.
• Misalignment also makes it
very hard to back up the
trailer.
• This is commonly called dogtracking.
Axle Offset
• Another problem is an axle
that is not centered with the
centerline of the vehicle.
• When an axle is offset and
the vehicle is driven straight
down a highway, the
steering wheel should be
centered and the vehicle will
not dog-track. However, as
soon as it is cornered, it will
oversteer in one direction
and understeer in the other.
Electronic Alignment Equipment
• Wheel/axle alignment
measurements can be taken
in a number of ways.
• A number of electronic
alignment systems exist.
• Electronic alignment
systems use computers to
analyze and display
alignment conditions.
• The electronic methods
include:
– Light beam alignment
– Laser alignment
Beam Alignment Systems
• Laser beam equipment
projects light beams onto
charts, scales, and sensors to
measure toe, caster, and
camber.
• The wheel-mounted light
projectors can be focused to
any length wheelbase and to
check alignment angles.
• Two- and four-wheel models
are available.
• Mirrors redirect the light
beams from the projector back
onto scales mounted in the
rear toe boxes of the
projectors.
Sensor/Computer Alignment (1 of 4)
• This shows an initial
analysis made by Hunter
WinAlign software as
displayed by a Windows
driven PC.
• WinAlign automatically
calculates the correction for
the technician.
• As the adjustment is made,
the arrow moves across the
bar graph target guiding the
technician.
Sensor/Computer Alignment (2 of 4)
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Sensors are mounted at each wheel
for fast, precise alignment.
Alignment readings, specifications,
and step-by-step instructions are
displayed on a display monitor.
Keyboard-entered specifications are
automatically compared against the
actual angles of the vehicle, with
the results displayed on the display
screen.
Specifications can be retained in
computer memory for future use or
on CD.
As adjustments are made on the
truck, these are automatically
displayed on the monitor, enabling a
high degree of precision.
Sensor/Computer Alignment (3 of 4)
• When the adjustment is within
spec, the bar graph changes
from red to green.
• A typical system provides for:
– Four-wheel alignment with
four sensors
– Two-wheel alignment with two
sensors
• All wheels are aligned to a
common centerline for precise
alignment.
• By moving instruments, the
system can also check both
rear axles of a tandem drive
axle, as well as the front
steering axle.
Sensor/Computer Alignment (4 of 4)
• Like the light beam system,
computer-controlled systems
can be adapted to align trailer
axles by using a gauge bar
attached to the trailer kingpin,
offering a much greater
degree of precision.
• Computerized alignment
systems make truck
alignments an exact science.
• They will also measure and
display frame offset angles.
• This allows technicians to true
truck and trailer chassis and
suspensions.
Warning
• All steering mechanisms are critical safety
items.
• A vehicle should be deadlined (OOS report)
when a defect is reported.
• It is essential that instructions in the service
literature are adhered to.
– Failure to observe these procedures may
result in loss of steering with life-threatening
results.
Warning
• When a vehicle is operated at temperatures
below 30°F with SAE 90 weight oil in a
manual steering gear, it can turn to a greaselike consistency, resulting in stiff, sluggish
steering.
• This can compromise accident avoidance
maneuvers because of slow steering
response.
• When operating in temperatures continuously
below 30°F, install a lighter oil in manual
steering gear, such as SAE 75 weight oil.
Shop Talk
• Before performing the remaining checks,
apply the parking brakes and chock the rear
tires.
• Raise the vehicle until the front tires leave the
pavement and then place safety stands
under the frame rails.
• Be sure that the stands will support the
weight of the vehicle.
Caution
• Before performing any servicing procedure
on the front suspension, set the parking
brake and block the drive wheels to prevent
the vehicle from moving.
• After jacking the truck up until the steering
axle wheels are raised off the ground,
support the chassis with safety stands.
• Never work under a vehicle supported only
by a jack.
Warning
• Do not drive the vehicle with too much lash in
the steering gear.
• Excessive lash is a sign of an improperly
adjusted steering gear or worn or otherwise
damaged steering gear components.
• Driving the vehicle in this condition could
result in a loss of steering control.
Manual Steering Gears
• A steering gear is often referred to as a
steering box.
– It is an assembly of gears contained within a
housing.
– Manual steering gears have lubricant within
the housing.
• Two basic types of manual steering gears are
used in heavy-duty trucks.
– Worm and sector shaft type
– Recirculating ball and worm type
Recirculating Ball Gears
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Mounted on the worm gear is a ball nut with internal spiral grooves containing
recirculating ball bearings.
The ball bearings transmit the turning force from the worm gear to the ball nut,
causing the ball nut to move up and down the worm gear.
Ball return guides are connected to each end of the ball nut grooves. These
allow the ball bearings to circulate in a continuous loop.
The ball nut also has exterior gear teeth that mesh with the sector gear.
As the ball nut moves up or down on the worm gear, it causes the sector gear
to rotate, which, in turn, causes the Pitman arm to swivel back and forth.
Power-assist Steering Systems
• A power steering system
must default to manual
operation in the event of
power-assist circuit failure.
• Truck hydraulic powerassisted steering systems
contain a dedicated pump
that delivers hydraulic fluid
under pressure to a powerassist steering gear.
• In a gear such as this, the
hydraulic control circuit is
located within the steering
gear so it is known as an
integral system.
Power Steering Pump
• The power steering pump is
used to produce the hydraulic
circuit flow required for the
power-assist to the steering
gear.
• They can be either gear- or
belt-driven, depending on the
engine application, but the
majority are gear-driven by an
engine accessory drive.
• Power steering pumps are
usually mounted near the front
of the engine.
• Most power steering pumps
are similar in construction.
Pump Operation
• Centrifugal force and hydraulic pressure loads the
vanes outward against an oval cam ring.
• As the rotor turns, the volume between vanes
changes.
• When they move past the inlet port, the volume
increases; oil is drawn in.
• As they approach the discharge port, volume is
reduced, creating pressure rise and oil is
discharged.
Flow Control
and Pressure Relief Valves
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•
•
•
The flow control valve regulates
pressure and flow output from the
pump to provide for consistent
power-assist during variations in
engine rpm.
When the engine speed
increases, the pump can deliver
more flow than is required to meet
system requirements.
When outlet pressure reaches a
preset level, the pressure relief
ball is forced off its seat, creating
a greater pressure differential at
the two ends of the flow control
valve.
This allows the flow control valve
to open wider, permitting more
pump pressure to flow back to the
pump inlet, and pressure is held at
a safe level.
Power Steering Gears
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Power steering gears are similar to
a manual recirculating ball steering
gear with the addition of a hydraulic
assist control mechanism.
The power steering gearbox is
charged with hydraulic fluid under
pressure and uses a rotary control
valve to control the flow of fluid.
The movement of the ball nut is
assisted by hydraulic pressure.
The integral-type power steering
has the rotary control valve and a
power piston integrated with the
gearbox.
The rotary valve directs the oil
pressure to the left or right chamber
to steer the vehicle.
The spool valve is actuated by a
lever or a small torsion bar located
in the worm gear.
Hydraulic Operation
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•
•
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The rotary control valve is an open-center type that allows a continuous flow of
oil when held in the neutral position by the torsion bar.
When steering effort is applied, the spring action of the torsion bar results in the
input shaft rotating slightly in advance of the ball screw.
The six pairs of grooves that form the rotary control valve are displaced from
their neutral flow position.
As steering effort increases, so does the amount of displacement.
Depending on the direction steered, the groove displacement of the input shaft
directs hydraulic oil through the appropriate drilled passages in the ball screw
to one side or the other of the piston.
Troubleshooting Safety
• Always block vehicle wheels. Stop the engine when working under
a vehicle. Keep hands away from pinch points.
• Never connect or disconnect a hose or line containing pressure.
Never remove a component or pipe plug unless all system pressure
has been depleted. The pressures used in truck hydraulic powerassist steering systems are massive and can peak at 1,500 psi.
• Never exceed recommended pressure and always wear safety
glasses. Never attempt to disassemble a component until after
reading and understanding recommended procedures.
• Use only OEM-suggested replacement components. Only
components, devices, and mounting and attaching hardware
specifically designed for use in hydraulic systems should be used.
Replacement hardware, such as hoses and fittings, should be of
equivalent size, type, and strength as the original equipment.
• Devices with stripped threads or obvious physical damage should
be replaced. Repairs requiring machining should not be attempted.
Caution
• As with manual steering gear, the Pitman arm
should NEVER be removed from the sector
shaft to center the steering.
– In some instances, this could require
disassembly of the steering gear.
Shop Talk
• A power steering analyzer is the preferred
method of assessing the performance of a
hydraulic power-assist steering circuit.
• The power steering analyzer consists of
hoses, quick release couplers, a flowmeter,
pressure gauge, and flow control valve.
Electronically Variable Steering
• Optimized power steering
control has the following
features:
– Improved steering wheel
road feel
– Directional stability
enhanced by a steering
effort proportional to
driving speed
– Reduced dry park effort at
the steering wheel
– Reduced system power
consumption
EVS Pump Design
• The EVS steering system uses a solenoidcontrolled variable-flow control concept.
• The pump assembly includes a highefficiency vane pump, flow control, and
proportional solenoid-type throttle valve.
• The system is designed with fail-safe
features.
– When the solenoid is not energized, flow is
low (at around 60 percent of its normal
capacity), similar to conventional power
steering systems.
EVS Electronic Control Unit (ECU)
• The purpose of the electronic controller is to change the PWM
actuation signal to the pump solenoid with respect to the roadspeed sensor signal.
• The controller incorporates switches that allow for three potential
operating modes with an LED display to assist in troubleshooting.
– ECONOMY MODE: In economy mode, flow control is at maximum
below 15 mph (24 km/h); at its minimum, above 50 mph (80 km/h); and
it decreases proportionally from 15 to 50 mph.
– NORMAL MODE: The normal mode has high flow at low speeds and
decreases as speed increases (similar to economy mode), except the
minimum flow is set at 13.6 L/min and is reached at about 40 mph (64
km/h). In this mode, the steering system acts much like a conventional
power steering system with 13.6 L/min flow control.
– STANDBY MODE: If the vehicle is stationary for longer than 10
minutes, the system switches into a standby mode. This mode reduces
flow to minimum power-assist as long as the speedometer indicates
zero. When road speed is detected, the system automatically switches
to its original mode.
PWM Actuation
• The PWM actuation circuit
operates the solenoid valve by
a fixed-frequency, pulse-widthmodulated signal with closedloop duty cycle control that
uses the solenoid current as
feedback.
• This ensures that the solenoid
positioning is relatively
constant with changes in
vehicle battery voltage.
• It also allows the controller to
provide current to the solenoid
directly from the battery
without need for high-current
voltage regulators.
Load-sensing Power Steering
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HYDRAULICALLY
CONTROLLED: This nonelectronic hydraulically controlled
load-sensing system has a
demand-type flow control that
uses steering load pressure to
control its variable-flow powerassist.
SPEED PROPORTIONING: This
system provides for speed
proportioning of flow to the
steering gear from a flowcontrolled pump.
Instead, the system relies on a
control strategy in which the
pressure requirement for power
steering is a function of vehicle
speed.
The load-sensing system is similar
to a conventional hydraulic powerassist circuit, except that a
modification has been made to the
flow-control section of the pump.
Combination
Flow/Relief/Load-sensing Valve
Summary (1 of 6)
• Steering systems used in trucks must deliver precise
directional control of the vehicle and its load, in both
loaded and unloaded conditions, and at highway and
park/stall speeds.
• Truck steering systems are either manual or powerassisted.
– Power-assist systems are required to default to
manual operation in the event of a loss in the powerassist circuit.
– Power-assist systems can use either hydraulic or airassist circuits.
• Improper steering adjustments and front-end alignment
can lead to suspension and tire wear problems.
Summary (2 of 6)
• A properly aligned front-end results in:
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Easier steering
Increased tire life
Directional stability
Less wear and maintenance on front-end components
Better fuel economy
Increased safety
• Ackerman geometry provides toe-out on turns,
permitting tires to roll freely during turns when each
travels through a different arc.
Summary (3 of 6)
• Axle alignment measurements can be taken in a
number of ways.
– Tram gauges and measuring tapes may be used as
can light or laser beam alignment systems with
computerized sensors and analysis.
• The most accurate and easiest to use alignment
systems in use today are computer-controlled and
feature in-memory specifications, step-by-step
instructions, and user-friendly displays. Keyboardentered specifications are automatically correlated
to the actual angles measured on a vehicle, with the
results displayed on the monitor screen.
Summary (4 of 6)
• Steering axle components should be inspected and
lubricated routinely on a preventive maintenance
schedule.
• Two general types of manual steering gear are used in
heavy-duty trucks.
– They are the worm and sector shaft type and the
recirculating ball and worm type.
• Some worm shaft preload is necessary to prevent
unwanted random movement within a steering system.
• Two types of steering gear preloads have to be
checked.
– Worm bearing preload and total mesh preload
Summary (5 of 6)
• Insufficient preload allows some lost motion in the
gearset, requiring the driver to turn the steering wheel
farther to get a steering response from the front
wheels.
– Excessive preloads result in hard steering, darting,
and oversteer.
• An integral power-assist steering system contains a
pump that delivers hydraulic fluid under pressure to a
power steering gear.
– The steering gear has an integral hydraulic control
valve that measures steering effort and responds to
provide the appropriate amount of assist in turning the
wheels.
Summary (6 of 6)
• A power-assist steering gear is fundamentally similar to
a manual recirculating ball steering gearbox with the
addition of a hydraulic assist: It must default to manual
operation in the event of a hydraulic circuit failure.
• Air-assisted steering systems use the vehicle
compressed air supply as a means of supplementing
manual steering operation. This is an external system
consisting of an air torque valve contained in a
dedicated drag link assembly and a double-acting
power cylinder.