Fig. 203.-Steering Gear of Worm and Wormwheel Type Used on Locomobile Cars.

are not costly to build and usually form the equipment on cheap, light cars where an irreversible steering gear is not absolutely necessary.

Q. What is an irreversible steering gear, and how does it differ from a reversible steering arrangement?

A. The irreversible forms of steering gears are those that utilize reduction gearing that is not capable of being turned except by the handwheel and which is therefore not affected by the action of the road wheels. As previously explained the simpler forms of steering

gear are reversible and movement of the front wheels is communicated directly to the hand lever or wheel, the constant movement of which is apt to tire the operator.

Q. Which is the best type and why?

A. The irreversible forms of steering gear, while slower acting than the simpler reversible type, are the most popular because they are the safest, the most easily handled, and the most powerful form. The wheels of the largest car fitted with an irreversible gear may be turned without difficulty by any person of average strength.

Q. Describe action of worm reduction steering gear.

A. Two forms of worm and worm gear reducing gearing are outlined at Figs. 203 and 204. They are similar in construction, except that one utilizes a complete worm gear to actuate the steering arm while the other employs a worm gear segment. The worm is carried at the lower end of the steering post, being restrained from end movement by ball thrust bearing at either side. It is keyed to the steering column so the worm must be turned with the hand wheel. The worm, as it revolves, rotates the worm gear to which the steering arm is secured and this is oscillated back and forth as the worm is turned. The motion imparted to the steering arm is transferred to the movable wheel spindles on the front axle by means of a drag link. While it is possible to turn the worm gear through the medium of the worm, the pitch of the thread on the latter is such that it is not possible to move the worm and consequently the handwheel used to operate it by moving the steering arm or wheels.

Q. What is a thread and nut steering arrangement?

A. The thread and nut steering arrangement differs from the worm type in that the end of the steering post is threaded with a coarse screw thread and pulls a nut up and down as it is rotated. As the nut is kept from turning it is apparent that it will be moved in one direction or the other and that this movement may be transferred to the steering wheels by means of a simple bell crank lever, the short arm of which is operated by the nut that works up and

down on the steering post, while the long arm performs the same function as the steering arm of a worm reduction gear.

Q. Why are the engine control levers usually carried convenient to the steering wheel?

A. The levers used to regulate the time of the ignition and the amount of gas supplied the motor are invariably placed convenient to the steering wheel so the motor speed may be regulated without removing the hand from the wheel rim, except for an instant. In some cases the levers are

placed under the steering wheel and are long enough so they may be moved without removing the hand from the wheel rim. In most cars the construction outlined at Fig. 205 is followed. The spark and throttle levers are carried above the steering wheel and operate on a fixed sector member which remains stationary whether the hand lever is turned or not. This means that the levers will always retain the same position unless moved by the operator.

Q. Name two common methods of front axle construction. A. The two general methods of front axle construction are shown at Fig. 206. The form outlined at A is a tubular axle, while that at B is a one-piece forging termed the I beam axle.

Q.

How are the various parts of a tubular axle assembled to form a unit?

A. The tubular axle is composed of a number of castings or forgings attached to a steel tube. In the construction shown at Fig. 206-A the steering yokes and spring chairs are separately

Fig. 206.-Typical Examples of Conventional Front Axle Construction. A Tubular Axle. B-I Beam Steel Drop Forging.

formed members which are pushed in place on the steel tube forming the axle proper and after being properly located are pinned in place and then brazed to the axle tube.

Q. What is the advantage of the I-beam axle?

A. The I-beam axle is forged in one piece with steering yokes and spring chairs formed integral and there is no possibility of these members becoming loose as sometimes occurs with poorly constructed tubular axles. The I-beam axle is the strongest construc

Steering Spindle.

Q. Name two

common type of steering knuckles.

A. The two forms of steering knuckles generally used are the Elliot outlined at Fig. 207 and the