The purpose of the steering gear is to change the rotational motion of the steering wheel to a reciprocating motion to move the steering linkage. There are three styles currently in use: the recirculating ball, worm and roller, and the rack and pinion. The latter gear assembly incorporates the already described rack and pinion link-age system and steering gear as a single unit. The recirculating ball is generally found in larger cars, A sector shaft is supported by needle bearings in the housing and a bushing in the sector cover. A ball nut is used that has threads that mate to the threads of the worm shaft via continuous rows or ball bearings between the two. Ball bearings recirculate through two outside loops, referred to as ball return guide tubes. The ball nut has gear teeth cut on one face that mesh with gear teeth on the sector shaft. As the steering wheel is rotated, the worm shaft rotates, causing the ball nut to move up or down the worm shaft. Since the gear teeth on the ball nut are meshed with the gear teeth on the sector shaft, the movement of the nut causes the sector shaft to rotate and swing the pitman arm. The design of two separate circuits of balls results in an almost friction-free operation of the ball nut and the worm shaft. When the steering wheel is turned, the ball bearings roll in the ball thread grooves of the worm shaft and ball nut. When the ball bearings reach the end of their respective circuit, they enter the guide tubes and are returned to the other end of the circuits. The teeth on the sector shaft and the ball nut are designed so that an interference fit exists between the two when the front wheels are straight ahead. This interference fit eliminates gear tooth lash for a positive feel when driving straight ahead. Proper mesh engagement between the sector and ball nut is obtained by an adjusting screw that moves the sector shaft axially. The worm thrust bearing adjuster can be turned to provide proper preloading of the worm thrust bearings. Worm bearing preload eliminates worrn endplay and is necessary to prevent steering free-play and vehicle wander. The sector can be either constant or variable ratio. The formers teeth arc all identical, while the latter has one long tooth between two shorter teeth that changes the amount of mechanical advantage according to the position of the wheel. This serves to make the steering faster (maybe 13:1) in turns than in a straight direction (15 or 16:1). Variable ratio is ordinarily used only in power-steering units. The worm and roller gearbox is similar to the recirculating ball except a single roller replaces the balls and ball nut. This reduces internal friction, making it ideal for smaller cars. The steering linkage used with a worm and roller gearbox typically includes a pitman arm, center link, idler arm, and two tie-rod assemblies. The function of these components is the same as the parallelogram steering linkage. In operation, the steering shaft rotates the worm gear. It, in turn, engages the roller, causing the roller shaft to turn. The shaft moves the pitman arm left or right to steer the vehicle. It must be noted that the steering gear does not cause the vehicle to pull to one side nor does it cause road wheel shimmy.
The purpose of the steering wheel and column is to produce the necessary force to turn the steering gear. The exact type of steering wheel and column depends upon the year and the car manufacturer. The steering column, also called a steering shaft, relays the movement of the steering wheel to the steering gear. The steering wheel is used to produce the turning effort. The lower and upper covers conceal parts. The universal joints rotate at angles. Support brackets are used to hold the steering column in place. Assorted screws, nuts, bolt pins, and seals are used to make the steering wheel and column perform correctly. Since 1968, all steering columns have a collapsible feature that allows the column to fold into itself, upon impact. This feature prevents injury to the driver. In most vehicles equipped with a driver's side air bag, the air bag assembly is contained in the center portion of the steering wheel. This assembly must be disarmed and removed before the steering wheel can be removed. Differences in steering wheel and column designs include fixed column, telescoping column, tilt column, manual transmission, floor shift, and automatic transmission column shift. The tilt columns feature at least five driving positions (two up, two down, and a center position). Both fixed and tilt columns may house an emergency warning flasher control, a turn signal switch, ignition key, lights (high /low beams), horn, windshield wipers and washers, and an antitheft device that locks the steering system. On automatic transmission-equipped vehicles the transmission linkage locks also. Methods used to lock the shaft to the tube include a breakaway plastic capsule or a series of inserts or steel balls held in a plastic retainer that allow the shaft to roll forward inside the tube. There are also collapsible steel mesh or accordion-pleated devices that give way under pressure. After the vehicle has been in an accident, the steering column should be cheeked for evidence of collapse. Although the car can be steered with a collapsed column that has been pulled back, the collapsed portion must be replaced. All service manuals provide explicit instructions for doing this. The steering wheel is usually held in place on the steering column by either a bolt or nut. When the blocked tooth on the steering gear input shaft is in the 12 o'clock position, the front wheels should be in the straight-ahead position and the steering wheel spokes in their normal position. If the spokes are not in their normal position, they can be adjusted by changing the toe adjustment. This adjustment can be made only when the steering wheel indexing mark is aligned with the steering column indexing marks. As a rule, indexing teeth or mating flats on the wheel hub and steering shaft prevent misindexing of these components. The alignment of the notches on the steering wheel hub and steering shaft confirm correct orientation.
The purpose of a steering damper is simply to reduce the amount of road shock that is transmitted up through the steering column. Steering dampers are found mostly on 4WD, especially those fitted with large tires. The damper serves the same function as a shock absorber but is mounted horizontally to the steering linkage-one end to the center link-the other to the frame
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