Q. How are the wheels driven when mounted on a stationary axle?

A. The wheel hubs are provided with sprockets which are connected to smaller sprockets carried by the axle shafts of the countershaft assembly by means of chains which transmit the power to each rear wheel.

Q. What is the advantage of this method of construction?

A. On heavy vehicles, such as motor trucks, which are designed to operate on solid rubber tires, it is desirable to suspend as much of the mechanism of the car as possible from the frame so the springs may absorb the larger portion of the jarring and jolting due to solid tires. As most of the heavier vehicles are designed to move slowly it is necessary to employ a double reduction system so the differ

Drive Sprocket

Stub Axle

!Stationary Axle Tube Spring Chair

Brake Rod

Ball Bearings

Fig. 183.-Simple Automobile Rear Axle of the "Dead" Type. ential and bevel gear drive assembly which provides the first speed reduction is part of the countershaft and the rear axle which must be strong and yet relatively light is called upon only to carry the car weight and not to transmit any of the engine power. Another reduction of speed is possible in addition to that obtained at the countershaft by making the driving sprockets smaller than the driven members carried by the wheel hubs. Owing to the use of a fixed rear axle member it is not necessary to carry any of the more or less delicate mechanism forming the differential and drive gearing as part of the axle and these portions of the drive system may be carried in a separate assembly attached to the spring supported frame members.

Q. Describe construction of simple type live axle.

A. A simple live axle of conventional design is outlined at Fig.

Fig. 184.-"Live" Automobile Rear Axle of Bevel Gear Drive Type. 184. This member not only supports the weight of the car, but also incorporates the power transmission and differential gearing. The power is taken from the gearset through a drive shaft revolving in roller bearings. At the end of the drive shaft a bevel pinion is secured which meshes with a bevel or ring gear carried by the differential housing. The differential assembly is also supported on roller bearings and shafts extend from the differential gears to the wheel hubs. All the rotating parts are housed, the differential and bevel gear assembly being mounted in a housing of malleable iron while the drive shaft and axle shafts A and B are protected and supported by a tubular axle housing, which is securely attached

to the differential housing at the center of the axle. In the simplest form of live axle construction the axle shafts not only transmit the power from the differential gears to the hubs but are called upon to carry the car weight at the rear end as well. This form of construction is suitable only for light and medium weight cars.

Q. How many types of live axle are used?

A. Live axles may be of a simple form, as previously described and shown at Figs. 184 and 185, or they may be of a semi-floating or full floating construction. The simple live axle shown at Fig. 185 is practically the same in construction and method of operation as that previously outlined with the exception that the axle shafts are carried on annular ball bearings instead of roller bearings. Q. What is the "semi-floating" axle?

A. The term "semi-floating" is applied to those forms of axles where the axle shaft is depended on to drive the wheels as well as take part of the load caused by thrust reaction, when the wheel skids sideways. An axle of this general form is outlined at Fig. 186, and it will be noted by comparing it with the form shown at 184 and 185 that the wheel hub is carried by a large bearing that is mounted on the drive axle housing so the axle shaft that is fastened in the wheel hub is not called upon to carry any of the car weight. It is, however, depended on to steady the wheel against side thrust. This form of axle construction is often called "the one bearing floating axle" because for all practical purposes it is a floating type inasmuch as the axle shaft may be withdrawn from the interior of the axle housing or the differential assembly removed without relieving the wheels of the car weight.

Q. What is the "full floating axle" construction?

A. The full floating rear axle construction, which is depicted at Figs. 187 and 188, differs from the preceding form inasmuch as the wheel hub is carried by two bearings which are in turn supported by the fixed housing member through which the drive axle passes. The driving axle is a floating member that is called upon only to transmit power and not to take any of the car weight. In the simple live axle forms the axle shaft revolves in bearings carried by the interior of the housing and as the wheels are secured to the shafts

supporting car weight these are subjected to much more strain than floating shafts.

In the true floating axle the drive axles may be removed by taking off a hub cap and pulling out the shaft. The wheel hub is not disturbed and the differential gear may be removed if desired without disturbing the wheels. In the live action construction of the simple form, the axle shafts can be taken out only by taking the entire axle assembly apart as outlined at Fig. 189. This means that the rear end of the car must be jacked up and the axle removed from the chassis in order to take it apart. The big advantage of the floating construction, especially in the forms shown at Fig.

Fig. 186.-Typical "Three-Quarter Floating" Rear Axle Having Driving Wheels Supported by One Double Row Bearing in Each Wheel Hub.

186 and 188, is that the differential and drive gear assembly may be removed for inspection or adjustment without disturbing the axle housings or taking wheels off. The axle shown at Fig. 187 utilizes double row ball bearings at all important points while that outlined at Fig. 188 employs single row ball bearings to carry the radial or direct acting loads while the end thrust caused by the bevel drive gears is taken by a ball thrust bearing used in combination with a single row at the ring gear side of the differential assembly. Q. How are the rear wheels driven in a simple live axle? A. The rear wheel hubs are usually provided with key ways which engage with driving keys carried by the live axle and are

kept from coming off either by means of pins passing through the hub and the shaft or by a clamping nut which forces the wheel tightly on the taper end of the live axle shaft.

Q. How are the wheels driven in a semi-floating axle?

A. The wheels of a semi-floating axle are driven by squared ends of the drive shafts which are a tight fit in a flanged member securely bolted to the wheel hubs. In some forms of axles the driving flange is formed integrally with the axle shaft and is securely bolted to the hub.

Q. How are the wheels driven in a full-floating axle?

A. When the full-floating construction is employed the live

Fig. 187.—“Full-Floating" Bevel Gear Drive Axle Having Driving Wheels Mounted on Two Ball-Bearings With All the Car Weight Carried on the Drive Axle Housing Tubes.

axle shafts carry positive driving clutch members of the male form which engage with a corresponding female member forming part of the wheel hub. The axle shaft is kept from working out by means of a threaded hub cap, as shown at Fig. 188.

Q. What is a combined live and dead axle construction?

A. Some designers endeavor to secure the advantages of the stationary form of axle and yet have the driving gears carried by the axle by using a combination construction in which a nonrotating member serves to carry the car weight while a live axle is attached to the fixed member and carries the differential gear