180 Auto Suspension and Steering
removed to gain access to the worm gear and nut during
overhaul. The adjuster can be located at either end of the
worm gear shaft.
Steering Ratio
The number of worm gear threads in relation to its
length determines the steering ratio of a conventional
steering gear. If there are many threads per inch, the worm
gear will be easy to turn (lower steering effort), but the
handling will be slow. If there are relatively few threads per
inch, handling will be quick, but steering effort will be
high. For example, to move the sector gear about 1/4 turn,
the steering wheel is turned about 4 turns. This gives a
steering ratio of about 16 to 1 (4 turns at the wheel divided
by 1/4 turn at the sector gear equals 16).
Variable Ratio Steering
Some conventional steering gears are equipped with
variable ratio steering. Variable ratio steering gears use
specially designed nut and sector gears. These gears taper
as the sector gear moves away from the center position.
See Figure 9-26. The sector is moved a relatively small
amount when it is in the center of its travel, which elimi-
nates overreaction when the steering wheel is first turned,
and reduces wander when traveling straight ahead. As the
sector gear moves further, the increasing taper of the
meshing gears increases the steering ratio. This makes hard
turns easier, especially in low speed situations such as
parking.
Types of Conventional Steering Gears
Three types of conventional steering gears have been
used in the recent past. They all make use of a worm gear
and a sector gear. The most common type is the recirculat-
ing-ball steering gear. Variations of the recirculating-ball
steering gear are used on all modern vehicles. An older,
less-used type is the worm-and-roller, which may be found
on some older cars, usually imports. A rare type is the cam
and worm, which is found only on older imported cars.
Manual steering versions of each type are discussed below.
Power steering versions of these gears will be covered later
in this chapter.
Recirculating-Ball Steering Gear
The recirculating-ball steering gear is commonly used
on modern vehicles. This steering gear is known by many
names, depending on the manufacturer. Common names
for this type of steering gear include worm and nut, worm
and ball, and recirculating nut and worm. No matter what
the name, the basic design is the same. The basic principle
of this type of steering gear is shown in Figure 9-27. The
worm gear is the screw, and the ball nut rides up and down
as the screw turns. Teeth on one side of the ball nut contact
matching teeth on the sector gear. When the steering shaft
turns the worm gear, the ball nut moves on the worm gear
shaft. Teeth on the ball nut cause the sector gear to turn.
The ball bearings between the threads of the worm
gear and ball nut reduce friction between the worm and
the nut. The steering gear is called a recirculating-ball
Jam nut
Sector gear–worm gear
clearance (lash)
adjuster
Adjuster
nut
Worm
gear
(preload)
adjuster
Steering gear
Worm shaft
Figure 9-25. A conventional steering gear box showing two
separate adjustment points. Always follow the manufacturer’s
recommended adjustment procedures. (General Motors)
Equal
length
teeth
Long
tooth
Nut
gear
Pitman shaft
sector
Constant ratio Variable ratio
Figure 9-26. Conventional steering gear box setup. This
illustrates the difference between a constant ratio gear and a
variable ratio gear. Note that the variable ratio pitman shaft
sector has a longer center tooth with a shorter tooth on each
side. (General Motors)
Balls and
guides
Adjuster
plug
Locknut
Worm
bearing
(lower)
Sector gear
Ball nut
Worm
bearing
(upper)
Oil
seal
Worm gear
(worm shaft)
Figure 9-27. Cutaway of a recirculating ball steering gear. Note
as the sector gear moves, the nut travels with it, causing the
worm gear to rotate. (Dodge)