Description & Operation
The steering gear is of the worm and recirculating ball type. A ball nut is used which has threads that mate to the threads of the wormshaft via continuous rows of ball bearings between the two. As the steering wheel is rotated, the wormshaft rotates, causing the ball nut to move up or down the wormshaft.
The gear teeth on the ball nut are meshed with the gear teeth on the sector shaft. Thus, the movement of the ball nut causes the sector shaft to rotate and swing the Pitman arm.
Proper mesh engagement between the sector and ball nut is obtained by an adjusting screw which moves the sector shaft axially. The worm thrust bearing adjuster can be turned to provide proper preloading of the worm thrust bearings.
There are two types of manual ball nut gears: A constant (24:1) ratio and a variable (20-24:1) ratio. Gears may be distinguished from one another by a model number stamped on the sector cover. "SMK-A" designates a constant ratio gear, while a "SMK-B" code is a variable ratio gear.