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Fig. 177-c.-Components of Distinctive Design Necessary to Successfully Apply the Four Wheel Drive Principle on Rambler Trucks. A.Section of Four Speed Gearset Having Drive Through Gears on All Speeds and Incorporating a Differential Drive Assembly to Impart Motion to the Axles. B.-Universal Joint Construction Utilized to Drive Wheel.

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Fig. 177-d.-Type of Wheel Used on Rambler Four Wheel Drive Truck.

wheel, and it is cla med that either set of two brakes is sufficient to hold the loaded truck on a 30 per cent grade. The wheel revolves on taper roller bearings carried by the wheel spindle. The steering knuckle is a special form of the inverted Elliot type and not only carries the wheel spindle but the frame supporting he spur driving pinion as wel. The loaded front axle is supported by a taper roller bearing at the lower end of the steering knuckle which makes it possible to turn the wheel with minimum exertion on the part of the operator. When the wheel is moved by the steering knuckle the frame carrying the spur drive pinion turns as well but owing to the universal joint the drive is not interrupted and the wheels are all

driven regardless of whether they are n a straight ahead position or at an angle to steer the car. Other vehicles have been evolved and applied as tractors for fire department service where the drive is through the front wheels only, these members being very similar in construction to the form described.

NOTE. For further information relative to power transmission see The Modern Gasoline Automobile." By Pagé.

LESSON TWENTY

DIFFERENTIAL GEAR CONSTRUCTION AND

OPERATION

Q. What is a differential gear?

A. A differential gear is a compensating mechanism interposed in the automobile transmission system to permit the traction members or driving wheels to turn at different speeds when describing

curves.

Q. Is a compensating arrangement needed on a wagon?

A. The ordinary forms of horse drawn vehicles do not need any compensating arrangement because all wheels are independent of each other and revolve on fixed axles.

Q. What would be the result if no differential gear was fitted to a four wheel automobile?

A. Without a differential gear the ordinary form of motor vehicle would be difficult to handle on curves and all parts of the driving mechanism as well as the tires would be subjected to severe stresses that would produce rapid depreciation.

Q. Where is the differential gear carried?

A. The ordinary form of differential or compensating gear may be incorporated as part of the gear set where this member is attached to the countershaft; as part of a countershaft assembly, even if the gearset is a separate unit, and as a part of a rear live axle if the direct drive system is employed.

Q. Can a practical automobile be made without a differential gear?

A. The only method by which a practical automobile can be constructed and dispense with a differential arrangement is to use but one rear driving wheel mounted in such a way that its point

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Fig. 178.-Parts of Typical Bevel Gear Differential and Their Relation in a Completed Assembly.

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