mobiles, the gears are in the form of rings which may be bolted to the shifting members and to flanges on the countershaft as shown at Fig. 336. The point advanced in favor of this construction is that it is possible to renew only the defective toothed ring instead of replacing an entire shifting member as is necessary when the gears. and hubs are formed integrally. It is also contended that the use of bolts to hold the gears firmly against flanges machined integrally with the countershaft makes for more secure attachment than the cheaper method of keying. The gear box design shown is used only on high-powered cars, where secure means of retaining the gears are absolutely necessary. A gear box of this design is very costly to manufacture, but it is cheaper to keep it in repair than the simpler forms. The change speed gearing is often combined on the rear axle, as shown at Fig. 337. This outlines a top sectional view through the rear construction and a side sectional view showing the disposition of parts very clearly. It will be observed that the bevel pinion carried on the back of the main shaft drives the bevel ring gear attached to the differential housing directly. As the gear box is part of the rear construction it is possible to secure exact alignment between the driving gears, and no power is lost due to faulty alignment between these members as may sometimes occur when the gear box and rear axle are separate components and the frame is distorted due to rough roads. A four speed gear box having clutch integral, a somewhat uncommon construction, is shown at Fig. 338. This design is used on some models of the Winton automobile. Three shifting yokes are used, shift member A controlling the direct drive, which in this case is a third speed, and the second speed. Shift member B gives the first or lowest forward speed and the reverse ratio. Shift member C is used to engage the fourth speed, which is a high ratio obtained through speeding up gears instead of reduction gears. With gear sets of this character all normal driving is intended to be done on the third speed or direct drive. The geared-up fourth speed is called upon only when conditions are favorable and high vehicle speed is desired. This gearset is a form in which but little clearance obtains between the shifting members and the non-shift ing gears, and is a form where depreciation of the shifting yokes may result in the gears grating even when in neutral position. In those forms of gear boxes where the ends of the shafts are supported by single row ball bearings with no special provision for end thrust, noisy action may result in a very short time due to misalignment of the ball bearings at the end of the shaft. Whenever the shifting members are moved to change a gear a pressure of from 75 to 100 pounds is exerted through the shifting yokes on Fig. 338.-The Winton Four Speed Sliding Gearset, Having Geared Up High Speed, and with Clutch Carried in Gear Case Extension. the sliding gear members, and if these do not engage promptly this pressure becomes an end thrust in the ball bearing. It is only when these are new and practically unused that this pressure can be resisted without pushing one of the ball races a trifle out of line with the other. As soon as the wear in a radial ball bearing amounts to a few thousandths of an inch, which does not appreciably affect the radial capacity of the bearing, the balls can yield to end thrust or lateral pressure to a certain extent and an endwise movement of the shaft results whenever an end thrust is applied due to poor engagement of the shifting gears. It is not only the pressure from the gear lever that must be taken into account, but the endwise shocks received in changing from a lower to a high gear also assist in producing depreciation at the bearing. The theoretically correct parallelism of the main and counter shaft is eventually lost if a suitable allowance in the dimensions of the different ball bearings does not serve to equalize the wear due to radial load in the ball bearings at both ends of each shaft. the gear tooth pressure is highest at the ends where it is trans'mitted with a large speed reduction to the low gear, this point applies specially to commercial vehicles in which the low gear is used more than in pleasure car service. Where the use of special end thrust bearings is considered too expensive, adjustable hardened end thrust.sustaining members, such as shown at Figs. 335 and 338, may be used at the ends of the countershaft. Owing to the lack of solidity of aluminum gear box castings, it is usually the plan in constructions of good design, such as at Figs. 332, 334 and 336, to mount the bearings in flange steel or bronze housings in order to enlarge the areas over which the bearing pressures are transmitted to the soft aluminum. Noisy gear box action is sometimes produced due to thin gear box walls which possess sound magnifying qualities, and this feature alone may multiply the volume of noise that would normally be caused by the gear action three or four times, especially if the bearings are located in such a way as to set the gear box in vibration when worn. The only way noise can be reduced is by keeping the ball bearings in proper condition and filling the gearset with a viscous lubricant, such as pure mineral grease, which will provide a cushioning effect against the vibration produced by roughness in either gears or bearings. |