The Washington herald., 1921-05-15
HARDEST WORKING
UNIT OF MACHINE
Is THE REAR AXLE
Three Classes-Floating,
Semi-Floating, Three
quarter Floating.
TAKES TWIST STRESS
Use no Grease, but Keep Filled
With Oil, and Drain and
Flush Occasionally


motor car is the rear axle. The
function of this part is not only to
help carry the weight of the car
but also to transmit the power.
rear axle is the scene of intense
mechanical activity. 1t will be OBJ
vious, then. that this part of the
mechanism should have the most
scrupulous care. 1t does not al
ways get it, as we shall point out
in the course of this article.
Rear axles fall readily into two
distinct cIassifications, dead aXles
and live ones. 1t is live axles which
are used on all modern passenger
cars. The term Tive" simply means
that the axle turns. Dead axIes do
not turn and they are only used on
vehicles having double chain drive
When we come to examine live
axles we find it necessary to class
ify them still further into three
minor classes, known respectively
as floating, semi-hoating, and three
quarter floating. A further classi-
hcation comes later, according to
the type of gearing used to trans
NIT the power.
The live axle consists principally
of a hollow spheroid. from which
project on either side two tubes. In
the central spherOid is located the
differential unit embodying a num-
Der of gears. From the differential
project two shafts, which occupy
the tubes projecting from the CEN
trail spherOid of the rear axle. At
the ends of these shafts the wheels
are attached.
Classification of AxIes.
The classifications of floating,
semifioating and three-qUarter
floating are derived from the meth
cd used in attaching the wheels TO
the shafts
The floating axle does do very
nearly that thing. 1t is not called
upon to bear any of. the weight o;
the car. it simply transmits the
power to the wheels and takes a lit
tie of the torsiona1 or twisting
stresses. The floating axle has II,
bearings outside the tube, so tina,
the wheels really rest on the tubes
and not on the shafts. In this type
of axle the shafts may be removed
without disturbing any other parts.
The semi-fioating axle has its
bearings on the inside of the tube
so that the shafts are called upon
TO bear some of the load as well a.
transmit power. The shafts are
not as easily removed as in the
case of the floating axle.
The three-quarter floating axle
has the bearings on tho outside OF
the tubes and there Is a rigid con-
nection between shafts and wheels
shall bear some of the load in addi-
tion to transmitting power.
When it comes to the types of
gears used in transmitting power
we find that the passenger cars OF
today employ three-straight bevel
spiral bevel, and two-speed beveI
In the truck field We find three ad-
dlttonal tyes-the worm, internal
gear. and double chain drive. though
the latter is growing less every
year. During the last few wears
the spiral bevel has come rapidly
to the front. until today it is the
most popular type. There are OBJ
viOus reasons for this. its quiet run
ming and general efficiency being
the leading ones. Many makers
still stick to the straight bevel,
while the two-speed bevel has only
one prominent adheTent.
Utmost Care Required.
The car owner who has expert
enced that most tenacious trouble
commonly. known as rear axle
trouble" will not need the advice
to do everything possible to guard
against it. Many serious troubles
may develop in this unit and only
the utmost care will obviate some
of them. Axle shafts sometimes
break or are twisted out Of their
proper shape. Bearings are some
times crushed. The differential
gears are peculiarly liable to chip
ping, which may very probably re-
suit in the ruin of the whole outfit.
As is generally the case, the prin-
cipal item in the proper care of the
rear axle Is fabrication. Never
make the mistake Of using grease
in this part, as used to be the rule.
Oil is the proper lubricant for the
rear axle Once or twice during
the running season the rear axle
should be drained. and after being
flushed out with kerosene fresh oil
should be put in. Note also that
while the part should be kept well
filled with oil all the time, an ex-
cess Is not desirable, for the extra
quantity Is likely to work down and
into the braking system, with the
functioning Of which IL interferes
Sometimes 1t is necessary to place
felt washers in the axle tubes to
prevent the excess oil working out
in this way. Many modern cars have
holes dfilled in the end of the tubes
to allow, excess oil to drain out. and
it Is possible to drill holes in this
way when they have not been pro-
vided by the car maker.
Function Involves Taking of Torque
Brt fabrication is not all in the
case Of the rear axle. As we noted
above. the function of this part in
wolves the taking Of torque or twist
ing stresses, which involve heavy
strains
If the shafts or other parts are
not heavy enough breakage occurs.
In case a part of the rear axle
mechanism breaks the proper thing
to do Is to find out the Fundamental
cause of the trouble. Mere re-
placement may not be enough. be-
cause IT is quite likely that there
may be a misalignment that will
quickly cause another breaka ce
after the new part is in place. The
only thing to do in a case of this
kind is to have the offending par,
lined up and that is a job for the
service station or an expert me-
chanic- When an intermittent hum
comes from the rear axle, 1t NAV
be accepted as a sign that the gear,
are running out of alignment and
the proper steps should at once he