Figure 8-20.Worm and sector steering gear.
An adjusting nut or plug is provided for adjusting the
end play of the worm gear.
Worm and Roller
The worm and rotter steering gear (fig. 8-21) is
quite similar to the worm and sector, except a roller is
supported by ball or rotter bearings within the sector
mounted on the pitman arm shaft. These bearings assist
in reducing sliding friction between the worm and
sector. As the steering wheel turns the worm, the roller
turns with it, forcing the sector and pitman arm shaft to
The hourglass shape of the worm, which tapers
from both ends to the center, affords better contact
between the worm and roller in all positions. This
design provides a variable steering ratio to permit
faster and more efficient steering.
Figure 8-21.Worm and roller steering gear.
"Variable steering ratio" means that the ratio is
larger at one position than another. Therefore the
wheels are turned faster at certain positions than at
others. At the center or straight-ahead position, the
steering gear ratio is high, giving more steering
control. However, as the wheels are turned, the ratio
decreases so that the steering action is much more
rapid. This design is very helpful for parking and
maneuvering the vehicle.
Cam and Lever
The cam and lever steering gear. in which the
worm is known as a cam and the sector as the lever, is
shown in figure 8-22. The lever carries two studs that
are mounted in bearings and engage the cam. As the
steering wheel is turned, the studs move up and down
on the cam. This action causes the lever and pitman
arm shaft to rotate. The lever moves more rapidly as it
nears either end of the cam. This action is caused by the
increased angle of the lever in relation to the cam. Like
the worm and roller, this design allows for variable
Worm and Nut
The worm and nut steering gear is made in several
different combinations. A nut is meshed with and
screws up and down on the worm gear. The nut may
operate the pitman arm directly through a lever or
through a sector on the pitman arm shaft.
Figure 8-22.Cam and lever steering gear