Section 9 - Steering Gear Assembly

The tension of the horn blowing ring, or load required on the ring to blow the horn, may be ad­justed by removing the ornamental cap in the center of the steering wheel, and turning the screws shown in Fig. 13, as necessary.
worm is welded integral to the wormshaft as shown in Fig. 14. The steering wheel is attached to the upper end of the wormshaft. The worm is mounted between two barrel type roller bearings, the lower one of which is adjustable toward the upper, for removing end-play in the wormshaft. Between the roller bearings, the worm is threaded with a pre­cision-finished helical groove.
The ball nut is bored to clear the outside diam­eter of the worm as shown in Fig. 15, and the bore is threaded with a precision-finished helical groove corresponding to that in the worm. Within the length of the nut the helical grooves are filled with special steel balls of 9/32" diameter (made to speci­fications specially drawn up for this steering gear). There are two complete ball circuits in the nut. To complete each circuit and keep the balls from running out at the ends, the nut is fitted with two tubular ball guides, each of which deflects the balls from their helical path when they reach the end of the nut, returning them to the helical path in the nut at the start of the circuit.
The two ball guides, together with the helical grooves in the worm and nut. thus confine the balls within two distinct closed circuits, one in each end of the nut. The balls within the helical path, 30 in each circuit, constitute a thread between the worm and nut, so that when the worm is turned, the nut moves along the worm, as with an ordinary screw thread. At the same time the balls roll freely between the worm and nut, circulating within their closed circuits, so that screw motion is obtained with rolling instead of sliding contact between the parts.
Rugged rack teeth are cut in that portion of the nut which faces the sector as shown in Fig. 14.
The sector shaft is mounted in anti-friction bronze bushings. A grease seal is provided near the outer end of the sector shaft. The sector is provided with rugged teeth which mesh with the rack teeth of the nut. These teeth are not ordinary spur gear teeth, but are produced by a special process to pro­vide true gear action between the rack and sector when the nut is located at a slight angle. With this construction, the adjustment for back-lash between the rack and sector teeth is very simple—all that is required is to shift the sector shaft slightly along its own axis by means of a convenient thrust screw, known as a lash adjuster.
The sector teeth are purposely cut in such a way that, when the sector is adjusted to remove all back-lash at the straight-ahead position of the front wheels, there will be a slight back-lash at each end of the sector travel, or when the wheels are turned far to the right or left of straight-ahead. In this way snugness of the sector in the rack teeth can be maintained with the wheels in
Fig. 13—Horn Blowing Ring Tension Adjustment
Turning the screws clockwise increases the ten­sion, and counterclockwise reduces it.
The truck steering gear, Fig. 14, is of the recir-culating ball type. Steering gear ratio on all con­ventional truck models is 19.8 to 1.
Fig. 14—Truck Steering Gear Worm. Nut and Ball Circuits
The principle working parts are the steering worm, the ball nut and the sector and shaft. Each of these parts is of heat-treated alloy steel. The





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