Propeller shafts may be solid or tubular type andrequire little or no maintenance.Solid shafts arenormally used where high shaft speeds are unnecessary.They are used extensively to power auxiliaryequipment, such as winches and hydraulic pumps. Thehollow shaft is used almost exclusively to transmitpower to the axles on automotive vehicles. The hollowshaft, because it rotates at high speed, must be balancedto prevent vibration and premature bearing failure in thetransmission and differential assemblies.A slip joint at one end of the propeller shaft takescare of end play.The driving axle, attached to thesprings, is free to move up and down, while thetransmission is attached to the frame and cannot move.Any upward or downward movements of the axle causesthe suspension springs to flex. This action shortens orlengthens the distance between the axle assembly andthe transmission. The slip joint makes up for thischanging vertical distance.The type of slip joint normally used consists of asplined stub shaft, welded to the propeller shaft, that fitsinto a splined sleeve in the universal joint, as shown infigure 2-12.UNIVERSAL JOINTSA universal joint acts as a flexible couplingbetween two shafts and permits one shaft to driveanother shaft that is at an angle to it. The universaljoint is flexible in the sense that it permits power tobe transmitted, while the angle of the shaft is beingcontinually changed.A conventional universal joint assembly iscomposed of three fundamental units: a journal (cross)and two yokes, as shown in figure 2-12. The two yokesare set at right angles to each other and are joined by thejournal. This design permits each yoke to pivot on thejournal, allowing the transmission of rotary motion fromone yoke to the other. As a result, the universal joint cantransmit power from the engine through the shaft to thedrive axle, even when the engine is mounted in the frameat a higher level than the drive axle, as shown in figure2-13.Universal joints need little, if any, maintenanceother than lubrication.Some universal joints havegrease fittings and should be lubricated according to themanufacturer’s specifications.CENTER SUPPORT BEARINGSWhen two or more propeller shafts are connectedtogether in tandem, their alignment is maintained by arubber-bushed center support bearing, secured to a crossmember of the frame. A typical center support bearingassembly is shown in figure 2-14. The standard bearingis prelubricated and sealed and requires no furtherlubrication; however, some support bearings onheavy-duty vehicles have lubrication fittings. The firstindication of support bearing failure is excessive chassisvibration at low speed caused by the bearing turningwith the shaft in the rubber support.FINAL DRIVESA final drive transmits the power delivered fromthe propeller shaft to the drive wheels or to sprocketsequipped on tracklaying equipment. Because it islocated in the rear axle housing, the final drive isusually identified as a part of the rear axle assembly.The final drive consists of two gears, called the ringgear and pinion. These are beveled gears, and theymay be worm, spiral, spur, or hypoid, as shown infigure 2-15.The function of the final drive is to change by 90degrees the direction of the power transmitted throughthe propeller shaft to the driving axles. It also providesa fixed reduction between the speed of the propellershaft and the axles driving the wheels. In passengerFigure 2-14.—Center support bearing.2-10
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