Chapter 25 Steering Systems 507
worm shaft is turned, the ball bearings impart an
axial (lengthwise of worm shaft) thrust to the ball
nut. Because the nut is prevented from turning, it
will travel one direction or the other, depending
on which way the worm shaft is turned.
As the ball bearings roll, they reach the end
of the groove in the nut and are forced through
a return tube. Eventually, they re-enter the nut
groove at the opposite end. This process accounts
for the name recirculating ball steering gear.
One side of the nut has gear teeth cut into it.
The pitman arm sector gear teeth engage the nut
teeth. When the nut travels one direction or the
other, the pitman shaft is forced to rotate. The
recirculating ball worm and nut steering gear
reduces friction to a very low level, making it a
very popular design.
Worm-and-Roller Steering Gear
A worm-and-roller steering gear is shown
in Figure 25-20. The pitman shaft engages the
worm by means of a roller with gear teeth cut
around it. The roller is mounted on antifriction
bearings. Because the roller is free to turn, the
friction developed in a wiping gear action is
bypassed. When the worm is rotated, the roller
teeth follow the worm and impart a rotary
motion to the pitman shaft.
Steering Gear Reduction
The amount of gear reduction in steering
gears depends on the vehicle type and weight,
the desired steering characteristics (fast or slow),
and the ultimate use of the vehicle. Steering gear
ratios will vary from 15:1 to 24:1. Steering wheel
movement will average from 4 to 6 turns to move
the wheels from full left to full right for standard
manual steering gears. The more turns needed
3
5
4
2
1
19
27
26
25
24
23
22
21
20
18
17
16
15
14
13
12
11
10
9
8
7
6
1-Top cover
2-Capscrew
3-Adjusting screw
4-Locknut
5-Filler plug
6-Washer
7-Gasket
8-Adjusting screw stop
9-Follower peg screw
10-Follower peg
11-Steering box
12-Inner column
13-Steering box bracket
14-Oil seal
15-Dust excluder
16-Pitman arm
17-Washer
18-Castellated nut and cotter pin
19-Worm gear
20-Bearings
21-Races
22-Gasket
23-Adjusting shims
24-End cover
25-Seal
26-Nut
27-Capscrew
Figure 25-18.
Exploded view of a worm and tapered pin (follower peg)–type steering box.
Goodheart-Willcox Publisher