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Show 7he AukmwStie SimpUjkd By an Automobile Expert It there is anything not clear to you, ask the automobile editor about It, An answer will be published on the completion of the articles pertaining to each section under discussion. LESSON NO. 50. . Propeller Shaft. As the engine is placed in the forward part of the car, while the wheels which are to be driven by the engine are placed some feet in the rear of the engine, the two must be connected by a shaft. This shaft is called the propeller shaft. Sometimes Some-times it is called the driving shaft, but this name is generally given to the driving driv-ing shafts in the rear axle. The propeller shaft is usually nothing more than a piece of solid round steel, though for lightness sake it is often a tube of steeL It itself requires no attention atten-tion and practically never gives trouble. The propeller shaft is connected to the power plant, and in most cars to the rear axle, by what is known as the universal joint, which might be defined as a device de-vice for transmitting revolving motion t designed. Let A Fig. 1 be one shaft and B the other at an angle thereto. let us next fasten to A a fork like arm C, and to B another, as D. If we could, now couple these two forks together in some way so that the shaft B could move up and down, with the fork U as a pivot, and A sideways, with the fork C as a pivot, our problem would be solved. This can be done by coupling them with a spider, spi-der, as shown in Kig. 4. , In Figs. 2 and 3, the coupled universal joint is shown. By observing Fig. 2., you will notice that the spider F is in a horizontal position, posi-tion, and that the fork I) and shaft B have swiveled on its pins. As the shafts make a quarter of a revolution the universal uni-versal will take the position shown in Fig. 3. Here you will notice that the spider lias swjveled on the fork C and is now at an angle to the horizontal. When the shafts have made but an eighth of a rods are so designed that thev Will not permit this. The propeller shaft is there-lore there-lore connected to one of the uulversals in such a manner as to be able to slide back and forth in it, which is usually done by having its end square, and fitting fit-ting it into a square hole in one of the universal. This Is shown in Fig. 5. In the Ford car the rad ius rods are so designed that, though the end of the nro-oll'?-- haft is square, it does not slide back and forth, and the pin passing t gii the hub of the universal and the shaft must not be left out, as it so often is. In order to take care of the lubrication, lubrica-tion, the universal is usually inclosed In a metal cover or housing, one end of which is ball shaped, and against which a shutter, equipped with a packing which will prevent grease working out, presses. Thla ls shown in Fig. 5 U being th housing in the shutter, and P the packing. pack-ing. The shutter is held pressed again!' the housing by the nut R. About once in every 5000 miles the pin? S should be unscrewed and the housing filled with grease, by means of a grease squirt-gun. In time, the packing P will wear. Therefore, each time the housing is filled with grease, or when grease is found spattered about near the universal, the nut R should be screwed up so as to take up this wear. If this is not done the grease will work out, resulting I" the bushings T and their pins wearing-This wearing-This wear will cause a bad knock and eventually the crushing of the bushing, and possibly also other "bad breaks. Keeping Keep-ing the universal joints packed with grease is extremely important, as the strain on them Is very great. They per-forni per-forni a difficult task. F.c, r F'C.2. from one shaft to another, when the axes of these shafts are at an angle to one another. an-other. The Universal Joint As the universal Is a "hard to get at" part of the car, its lubrication is seldom properly looked after, o manufacturers have finally designed a joint which can he packed with enough, grease to last for many thousand miles, and which is as nearly '"neglect proof" as possible. Why do we need the universal joint? The rear axle is attached to the frame by means of springs and so the height of the frame above the axle is constantly changing, and therefore the angle of the propeller shaft to the crank shaft of the engine will constantly be changing. This makes it impossible to have these two shafts in a straight line at all times, and therefore the universal which will drive ! through the varying angles, must be j used. In most cars the propeller shaft will he in line with the engine shaft, when the car is fully loaded, but must, because of the spring action, then be at an angle when only partially loaded. Tj4't us see how the universal joint is . revolution, the propeller shaft will have partly swiveled on the spider, and the spider will have partly swiveled on the fork of the driving shaft. Thus, you -see that by means of this double swivel the shaft will be driven even 'when at an angle. It is found that for one-quarter of a revolution the driven shaft will be slightly slight-ly retarded, while for the next quarter it ! will be slightly accelerated, then it will j again be retarded and again accelerated, BO that the drive of the rear wheels wlU j not be absolutely uniform. To overcome this difficulty two unlversals are general- ly used, the forks on each end of the I propeller shaft being placed at right angles to one another. In this way the j retarding action of the one will come during the acoelenfting action of the other, thus equalizing the fault and giving I a uniform drive. Were tiie propejler shafl positively con- 1 nee ted to the universal joint, then the rear axle, as It moves up and down with ; respect to the frame, would have to move 1 through an arc of a circle, the center of which is the front universal. In many I cars tiie springs, torque arm or radium. i |