Two tie-rod assemblies (fig. 8-19) are used to
fasten the center link to the steering knuckles. Ball
sockets are used on both ends of the tie-rod assembly.
An adjustment sleeve connects the inner and outer tie
rods. These sleeves are tubular in design and threaded
over the inner and outer tie rods. The adjusting sleeves
provide a location for toe adjustment. Clamps and
clamp bolts are used to secure the sleeve. Some
manufacturers require the clamps be placed in a certain
position in relation to the tie rod top or front surface to
prevent interference with other components.
One purpose of the steering mechanism is to
provide mechanical advantage. In a machine or
mechanical device, it is the ratio of the output force to
the input force applied to it. This means that a
relativety small applied force can produce a much
greater force at the other end of the device.
In the steering system, the operator applies a
relatively small force to the steering wheel. This action
results in a much larger steering force at the front
wheels. For example, in one steering system, applying
10 pounds to the steering wheel can produce up to 270
pounds at the wheels. This increase in steering force is
produced by the steering ratio.
The steering ratio is a number of degrees that the
steering wheel must be turned to pivot the front wheels
1 degree. The higher the steering ratio (30:1 for
example). the easier it is to steer the vehicle, all other
things being equal. However, the higher steering ratio,
the more the steering wheel has to be turned to achieve
steering. With a 30:1 steering ratio, the steering wheel
must turn 30 degrees to pivot the front wheels 1 degree.
Actual steering ratio varies greatly, depending on
the type of vehicle and type of operation. High steering
ratios are often catted stow steering because the
steering wheel has to be turned many degrees to
produce a small steering effect. Low steering ratios,
called fast or quick steering require much less steering
wheel movement to produce the desired steering
Steering ratio is determined by two factors
steering-linkage ratio and the gear ratio in the steering
mechanism. The relative length of the pitman arm and
the steering arm determines the steering linkage ratio.
The steering arm is bolted to the steering spindle at one
end and connected to the steering linkage at the other.
When the effective lengths of the pitman arm and
the steering arm are equal, the linkage has a ratio of 1:1.
If the pitman arm is shorter or longer than the steering
arm, the ratio is less than or more than 1:1. For
example, the pitman arm is about twice as tong as the
steering arm. This means that for every degree the
pitman arm swings, the wheels will pivot about 2
degrees. Therefore, the steering linkage ratio is about
Most of the steering ratio is developed in the
steering mechanism. The ratio is due to the angle or
pitch of the teeth on the worm gear to the angle or pitch
on the sector gear. Steering ratio is also determined
somewhat by the effective length and shape of the teeth
on the sector gear.
In a rack-and-pinion steering system, the steering
ratio is determined largely by the diameter of the
pinion gear. The smatter the pinion, the higher the
steering ratio. However, there is a limit to how small
the pinion can be made.
MANUAL STEERING SYSTEMS
Manual steering is considered to be entirely
adequate for smatter vehicles. It is tight. fast, and
accurate in maintaining steering control. However,
larger and heavier engines. greater front overhang on
larger vehicles, and a trend toward wide tread tires
have increased the steering effort required. Steering
mechanisms with higher gear ratios were tried, but
dependable power steering systems were found to be
the answer. There are several different types of manual
steering systems, which are as follows:
Worm and sector
Worm and rotter
Cam and lever
Worm and nut
Rack and pinion
Worm and Sector
In the worm and sector steering gear (fig. 8-20),
the pitman arm shaft carries the sector gear that meshes
with the worm gear on the steering gear shaft. Only a
sector of gear is used because it turns through an arc of
approximately 70 degrees. The steering wheel turns
the worm on the lower end of the steering gear shaft,
which rotates the sector and the pitman arm through the
use of the shaft. The worm is assembled between
tapered rotter bearings that take up the thrust and toad.