The Birmingham age-herald., 1918-08-18

by competent designers in passenger car work at the present time.
 Now it happens that the building of rear axles has passed nearly exclusive ly into the hands of specialist manufac- turers, who concentrate on this particu- lar part. In the main the rear axles turned out today are satisfactory But it is very easy thing for a car manu- facturer who wants to save money to buy a part that may be good enough in itself, but is not quite up to the work 1t will be called upon to do in that partic- ular car The car with an undersized axle will be constantly in trouble and the owner will get little satisfaction from it. The man who goes into the market to buy a car cannot be expected to know from examination whether or not the rear axle of the vehicle he buys is up to
 it's work. He cannot tell whether it has big enough bearings. The only safe way is to buy from recognized company with a reputation to sustain, so that it
 is certain that no skimping on parts to save a few dollars has been indulged in. That same advice holds good for all the other obscure parts of the car, where the purchaser cannot possibly make a person. al survey and must trust to the in tegrity of the manufacturer, who stands behind the car.
 CLASSIFICATION OF AXLE
 We noted previously that a further classification of live rear axles was necessary according-to the type of gear- ing used to transmit the power to the wheels. These classes are straight and spiral bevel worm, internal gear, tWo- speed bevel, single chain and double re- duction. It is scarcely necessary here to draw the distia :tion any finer, though engineers have further segregatons. as, for instance. the division of worm gears into those actuated by roller and by si- lent chain.
 In passenger car practice of today only three of these gearing types are used, the bevel, spiral bevel and the two-speed this latter only on one or two cars. In the motor truck field the bevels, worm single and double chain double reduc- tion and internal gear, all find place Within the past few years the spiral bevel has made such strides in the pas senger car field that it now predominates This type has skewed teeth and IS re- markable quetness in operation is it's great asset.
 Now for the cars needed to keep this hard Working assembly up to it's strenu- ous task Axle shafts sometimes twist and bend in service, and have even been known to break off sharply as If cut by a saw. Bearings are sometimes crushed, the differential gears the driving pinlon and the ring gear are liable to chipplng, which soon brings about the destruction
 of the whole unit. Naturally, as in most other parts of the mechanism the most
 important factor in keeping the rear axle up to snuff is fabrication. The twisting action or torque, to which the rear axle
 is subjected ill service, is likely to cause breakage of several sorts. In case any part breaks, it is vitally important not to replace the broken part until It has been ascertaned just what caused the accident. Some unit may very probaoly have gotten out of alignment and in this case replacement of a part will 10 no good for the fundamental cause of the trouble remains and the part will soon break again. The humming that is fre- quently heard in rear axles is generally caused by mi 5alignment of the gears, unless indeed it is induced by actual breakage of the gears. So, when break age occurs in the rear axle, the whole unit should be checked for alignment and this should be done by an exnert GEARS BECOME CHIPPED In the couse of su,i eUrvioe as the rear axle is called upon to do, i, is not sur prising that the teeth of tho gears should become clipped. SometimeJ these chips of metal are small, sometimes large,
 but they are always injurious as they get down between the StIi sound teetA and cause trouble. It is for this reasol that caution is always given that Ill changing the lubricant. in the rear axle housing the case should always be flushed out with kerosene before the fresh oil $ installed.
 Some owners in their anxiety to give the rear axle plenty of lubricant. overdo the matter. This is bad, because the ex
 cess lubricant inevitably works its Aay along the housing into the brake drums. impa iring the efficiency of those parts. In many of the newer aXles this has been provided against by the installation of a
 barrier to divert the course of the oil, Or by drilling a small hole for the oil to run out In cases where the axle is not so constructed, it is possible to install felt washers in the end of the tubes that effectually keep the oil back. Where this leakage into the brake crums is a long standing trouble. it is possible to drlli small holes near the spring seats to drain out the excess oil but before resortinS to this the felt washers should be tried out ana they will generally do the trick. Rear axle trouble makes it's presence known by appeal to the ear. Peculiar
 noises of any sort are to be taken as dan ger signals. Incidentally. unless the car owner is a full -fledged mechanic he vii.