Steering system works

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1
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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OBJECTIVES:
After studying Chapter 89, the reader should
be able to:

• Prepare for ASE Suspension and Steering (A4)
•
•
•

certification test content area “A” (Steering

System Diagnosis and Repair).
Discuss steering columns and intermediate
shafts.
Explain how a recirculating ball-nut and worm
gear steering gear system works.
Describe how a rack-and-pinion steering gear
works.

2
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

©©2008
2009Pearson
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KEY TERMS:
collapsible column • flexible coupling • gear lash

inflator module • kickback • lock plate • overcenter
adjustment
pinion torque • pitman arm • pitman shaft • preload
rack and pinion • rack support
sector gear • sector shaft • steering shaft • stub shaft
telescoping steering column • tilt steering column
universal joint • variable ratio • worm gear
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

3

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When the driver turns the steering wheel in a circle, or
in a rotary motion, the steering linkage moves side to

side, or in a lateral motion, to steer the wheels.

4
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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STEERING WHEELS
The steering wheel, which consists of a rigid rim and a number
of spokes connecting the rim to a center hub, attaches to the
top of the steering shaft at its center.
Most steering wheel hubs have internal splines that fit over
external splines on the steering shaft. A bolt or nut at the
center of the hub secures the wheel to the shaft.
The steering wheel may also contain controls for the cruise

control and audio controls, as well as the driver’s airbag.

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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Horn Operation The horn circuit is in a series circuit in which
current has one path that it can follow when the circuit is complete.
A normally open switch in an electrical circuit is inside the horn
button. When the driver pushes the horn button, the contacts on the
switch close, allowing electrical current through the circuit to
operate the horn.

A relay circuit is a more common method of wiring the horn. In a
relay, closing a switch in a low-current series circuit triggers the
high-current circuit that powers the horn.
See Figure 89–1.

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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Figure 89–1 The horn button is a normally open (NO) switch. When the button is depressed, the
switch closes, which allows electrical current to flow from the battery to sound the horn. Most
horn circuits use a relay to conduct the horn current.

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

7
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Airbags An airbag is made of nylon cloth covered with neoprene,
folded and stored in the center of the steering wheel. In a front-end
collision, the airbag inflates to provide a cushion between the
driver and the steering wheel and dashboard.
Figure 89–2 The airbag inflates at
the same time the driver moves
toward the steering wheel during a
front-end collision and supplements

the protection of the safety belt.

The part of the steering
wheel where the airbag
is stored is called the
inflator module.

The module also contains an
igniter, a canister of
flammable gas, and sodium
azide pellets.
Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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The sodium azide pellets burn quickly, and rapidly release nitrogen
gas, which fills the airbag. As it inflates, the airbag tears open the
module cover and spreads out across the steering wheel,
windshield, and dashboard.
The entire process, from sensor reaction to full airbag deployment,
takes 30 to 65 milliseconds. Within one second of inflating, the bag
deflates partially. Once deployed, an airbag cannot be reused.
Electrical current is provided to the airbag through the spiral cable,
which is also known as a coil. The spiral cable is a tightly coiled
metal strip that connects to the airbag module with two wire leads
and allows steering wheel rotation while maintaining electrical
continuity.
See Figure 89–3.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

Continued

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CAUTION: Whenever working on the steering column, consult service
information for the recommended airbag disabling procedure.

The module fits in front of the nut that secures the steering wheel to
the steering shaft. Bolts at the back of the steering wheel fasten the
airbag module to the steering wheel.
Figure 89–3 The airbag module attaches to the
steering wheel and is removed as an assembly
to service the steering wheel
and column.

10
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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STEERING COLUMNS
The steering shaft transmits rotary motion from the steering wheel
to the steering gear, while the column jacket that encases it
attaches to the vehicle body and offers a stationary mounting point
for a number of switches and mechanisms.

Figure 89–4
The steering shaft links the steering wheel to the
steering gear while the column jacket, which surrounds
part of the shaft, holds support brackets and switches.
This steering shaft has a small intermediate section
between the main section and the steering gear.
Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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Steering Shaft The steering shaft extends from steering wheel to
steering gear. A bolt or nut secures the shaft to the steering wheel,
and a flexible coupling joins it to the steering gear input shaft.
Figure 89–5 A pot joint is a flexible coupling used
to join two shafts that allow plunging motion.

The coupling can be a rubber or fabric insert, a universal joint
(U-joint), or a pot joint. A In pot joint permits a directional
change of the shaft, and a limited plunging motion.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

Continued 12

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Universal Joint A U-joint or universal joint consists of two
yokes with a steel crosspiece joining them together.
Universal joints allow changes in the angle between two rotating
shafts. In a steering shaft, U-joints allow rotary motion transfer
between the steering wheel and the steering gear even though the
steering shaft meets the steering gear input shaft at an angle.
On some models the steering shaft itself is assembled in sections
that are connected by U-joints. This permits the steering shaft
to bend around obstacles between the steering wheel and the
steering gear.
See Figure 89–6.
Continued 13
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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Figure 89–6
A typical intermediate steering shaft assembly showing a U-joint and related components.

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

14
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Flexible Coupling A flexible coupling is a simple device made
of rubber, or rubber reinforced with fabric, that is placed between
two shafts to allow for a change in angle between them.
The rubber in a steering shaft flexible coupling absorbs vibrations
and helps keep the steering wheel from shaking. A fail-safe
connection between the steering shaft and the steering gear
input shaft keeps the two shafts linked should the rubber
coupling wear out or break.
This allows the driver to maintain steering control, although the
steering feels loose when this happens.
See Figure 89–7.
Continued 15
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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Figure 89–7
A flexible coupling is used to isolate road noise and vibration from the steering shaft.

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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Column Cover To keep wiring from jacketmounted switches out of sight, the part of
the steering column extending into the
passenger compartment is shrouded.
Figure 89–8 Steering column covers are often
part of the interior trim.

Continued

A knee bolster under the column is a
safety feature to keep the driver from
sliding forward during a collision,
required for U.S. safety standards.

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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Collapsible Column Federal
law requires that all vehicles
sold in the US have collapsible
columns, steering columns and
shafts that collapse during a
collision to absorb crash energy
and lessen danger of injury.
Figure 89–9 Collapsible steering columns
include a mesh design that crushes easily, a
bearing design that allows one section of the
column to slide into the other, and a breakaway
device that separates the steering column from
the body of the vehicle in the event of a frontend collision.

During a collision, the smaller
section slides down into the
larger one to collapse like a
telescope.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

Continued 18
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Do Not Pound On the Steering Column
Always use a steering wheel puller and/or the special tools recommended
by the vehicle manufacturer when servicing the steering column. If a
hammer is used on the steering shaft in an attempt to remove a steering
wheel, the shaft could collapse, requiring the replacement of the entire
steering column assembly.

One early method used a section of the steering column constructed
out of mesh, which would collapse easily during a crash.
Another method is to use a two-piece column. One section of the
column has a smaller diameter so that it fits inside the other and rides
on a roller bearing.

19
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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2009Pearson
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Tilt Mechanisms Many steering columns have tilt mechanisms,
which allow the driver to adjust the angle of the steering wheel
relative to the steering column.
In a typical tilt steering column, the steering shaft has a short
section at the top joined to the rest of the steering shaft either by a
U-joint or gears.
Most tilt mechanisms are some sort of ratchet device that enables
the driver to lift the steering wheel and the top section of the shaft
and place them in the desired position.
See Figure 89–10.

Continued 20
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition

By James D. Halderman

©©2008
2009Pearson
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