The recirculating ball is the most common type of
worm and nut steering gear (fig. 8-23). In this steering
gear, the nut, which is in the form of a sleeve block, is
mounted on a continuous row of balls on the worm gear
to reduce friction. Grooves are cut into the ball nut to
match the shape of the worm gear. The ball nut is fitted
with tubular ball guides to return the balls diagonally
across the nut to recirculate them, as the nut moves up
Figure 8-23.Worm and nut steering gear (recirculating ball
and down on the worm gear. With this design, the nut is
moved on the worm gear by rolling instead of sliding
contact. Turning the worm gear moves the nut and
forces the sector and pitman arm shaft to turn.
Rack and Pinion
The rack-and-pinion steering gear has become
increasingly popular on smaller passenger vehicles. It
is simpler, more direct acting, and may be straight
mechanical or power-assisted.
The manual rack-and-pinion steering gear
basically consists of a steering gear shaft, pinion gear,
rack. thrust spring, bearings, seals, and gear housing.
In the rack-and-pinion steering system the end of the
steering gear shaft contains a pinion gear, which
meshes with a long rack (fig. 8-24). The rack is
connected to the steering arms by tie rods, which are
adjustable for maintaining proper toe angle. The thrust
spring preloads the rack-and-pinion gear teeth to
prevent excessive gear backlash. Thrust spring tension
may be adjusted by using shims or an adjusting screw.
As the steering wheel is rotated, the pinion gear on
the end of the steering shaft rotates. The pinion gear
moves the rack from one side to the other. This action
pushes or pulls on the tie rods, forcing the steering
knuckles or wheel spindles to pivot on their ball joints.
This turns the wheels to one side or the other so the
vehicle can be steered.
Figure 8-24.Rack-and-pinion steering gear.