OCR Text |
Show SPEED lira - AND THE PROPER HEJF SAME Occasional Inspection of Subsidiary Mechanical Device De-vice Insures Long Life; Function Explained. Among the subnldlary mechanical units Of the modern motor car, which only gives trouble on occasion, must he included the speedometer. In spite of the delicate nature na-ture of this Instrument, it is not often that the motorist has occasion to attempt repairs of It. However, when such an occasion does arise, some knowledge of the device is essentlaJ. At the present time there are In service serv-ice four deflni te types of speedometers, magnetic, centrifugal, hydraulic and that driven by air current. The magnetic type of speedometer is probably the most pop- ular type, as far as the number of makes of cars on which tt finds a place. A typical typi-cal construction In this class employs but one moving part, a circular magnet. Over this magnet, hut not touching It, is an inverted metallic cap, on the rim of which are a row of figures, indicating the miles per hour. The magnet is revolved by means of a flexible shaft, its Held acting on the dial cup. As the speed of the magnet lnoreaeejj, so does the magnetic pull, and the dial cup is drawn around to indicate the Increasing speed. The dial Is mounted on a steel shaft with a Jeweled bearing at the top. A hairspring Is fitted to rtsslst the pull of the magnet and this also serves to return the cup to earo when the car stops. In general, a temperature compensator Is fitted in this type, to prevent the hairspring being affected by climatic changes. Within the past year or so the air cur-I cur-I rent type of Hpeedometcr has been achieving achiev-ing a considerable popularity. This typo of Instrument employs a stream of air to turn the dial, which indicates the mileage. mile-age. A typical construction in this class has a flexlhlo shaft drivrrig an air circulator, cir-culator, consisting of two elongated aluminum alu-minum gears, placed in the head1 of the Insirument and opening into an air chamber. cham-ber. This latter lias two openings, one an entrance for the air, the other an exJt A dial fitted with a vano is pivoted in the chamber. A current of air is forced Into the chamber by the revolutions revolu-tions of the gears, and this stream striking strik-ing the vane, revolves the dial to show appropriate figures. A hairspring is used to return the dial to zero when the car stops. Centrifugal Type. The centrifugally operatefl speedometer Is actuated on the same principle found in tho fly ball governor. Weights are mounted on the moving shaft by means of levers or cranks, so that the movement of the weights by centrifugal force la communicated com-municated through the shaft to the dial. When the car speed increases these weights tend to fly out, and being connected con-nected with the dial through the shaft, pull the former around to the right and display the corroct figures for the miles per hour. The hydraulic type of speedometer has not gained any considerable following as yet, though its many excellent qualities may eventually win ft recognition. All speedometers have certain characteristics charac-teristics in common ; the variations in type generally refer to the means employed em-ployed of actuating the mileage dial. AH these instruments have a connection in the shape of a rotating shaft that is flexible and is housed in a flexible housing, running to some running part of the mechanism, usually a front wheel. On the end of this shaft Is a gear, which meshes with a gear on the moving part employed. This shaft is driven from the car's mechanism and in turn it drives the mechanism of the speedometer through some sort of a joint. It has, in the past, been the practically universal custom to connect the speedometer with a front wheel, but recently the Idea of utilizing .the propeller shaft has come Into marked favor. Now some makers are beginning to connect the speedometer with the transmission unit and claims of maximum quiet, perfect lubrication and protection are made for this location. When something goes wrong with the internal economy of the speedometer itself, it-self, the car owner can do nothing but take It to the service station. He would stand just as much chance of repairing his watch as this Instrument. However, there are other derangements that he can repair. For instance, the coupling at the bottom of the speedometer head sometimes shakes loose, so that while the shaft still revolves, the dial does not register anything. To fix this, the end of the shaft should be loosened from the head, pushed firmly in place and tightened tight-ened again. Again the flexible shaft may bind in the housing, due to abrupt bends, and then the speedometer will fall to register. reg-ister. When trouble occurs, look first at the shaft and see that it has as few bends in it as possible, and those long and sweeping. Tire Size Important. Another thing to watch is in making a change from one sized tire to another, on the wheel that drives the speedometer; speedome-ter; this will make the readings inaccurate. inaccu-rate. Even a change to oversize tires will canse Inaccuracy. For Instance, in one make of instrument, the makers announce an-nounce that If a change is made from 34x4-inch tires to 35x4, the sixty-eight sixty-eight toothed gear used in the former will have to be changed to a seventy-tooth seventy-tooth gear. It sometimes happens that where the driving gears are of fiber, a noise is caused by loosening of the parts. By using a little strong lailndxy soap, the gears may be swollen again, so that they mesh better. It Is a good thing to give the moving parts a little oil from time to time, but where the gears run exposed ex-posed this will not be very effective. In some cases, after the speedometer has been in service for some time, the dial begins to fluctuate, a condition induced in-duced by vibration. In some instances this becomes a chronic condition, but again it may simply be due to looseness in the fastenings and connections, which the service station will fix in a jiffy. If the speedometer suddenly fails to register reg-ister mileage and speed, the first place to examine is the driving shaft. Disconnect Discon-nect the flexible shaft at the head, and. with the front wheel being revolved, see if the shaft revolves without jerking. If the shaft runs smoothly, the trouble lies in the instrument itself. It happens sometimes that a link in the shaft is broken, so that when the part is disconnected dis-connected in this way the broken ends will catch at intervals- While the shaft is disconnected, turn it in the head and see if it makes the dial indicate. |