purpose of the axle shaft is to transfer driving torque from the differential
assembly to the vehicle's driving wheels. There are two types of axles: dead and
drive or live.
DEAD AXLE The dead axle does not drive a vehicle. It merely supports the
vehicle load and provides a mounting place for the wheels. In automotive
operation, dead axles are usually on trailers and tandem-type axle vehicles.
DRIVE OR LIVE AXLE The main purpose of the drive or live axles is to
transfer torque from the differential to each driving wheel. Depending on the
design, rear axles can also help carry the weight of the vehicle or even act as
part of the suspension. Most driving axles are enclosed in a housing. This
housing is usually of a three-piece design. The two axle housings are pressed
into the differential housing and then welded in place. Welding the three pieces
together makes the axle housings and differential housing a single unit. A
variation of the driving axle is the open axle shaft. In this design, the axle
shaft is not enclosed in a housing. Instead, it is part of the suspension system
and moves up and down with changing road conditions.
types of driving axles are commonly used: semifloating, three-quarter floating,
and full-floating. All three use axle shafts that are splined to the
differential side gears. The combination of the driving axles and the
differential is known as the final drive. At the wheel ends, the axles can be
attached in any one of a number of ways. This attachment depends on the type of
axle used. The differences between the three types actually lie in the manner in
which the shafts are supported on bearings and the way they are attached to the
Semifloating Axle Shafts
Semifloating axles help to support the weight of the vehicle. The
differential assembly is supported by tapered roller bearings and the axle
housing. The semifloating axle shafts are not affected by stresses associated
with the differential's operation.
inner ends of the axle shafts are splined to the axle side gears. The axle
shafts transmit only driving torque and are not acted upon by other forces.
Therefore, the axle shafts are said to be floating.
driving wheels are bolted to the outer ends of the axle shafts. The outer axle
bearings are located between the axle shaft and axle housing. This type of axle
has a bearing pressed into the end of the axle housing that supports the axle
shaft. The axle shaft is held in place with either a bearing retainer belted to
a flange on the end of the axle housing or by a C-shaped washer that fits into
grooves machined in the splined end of the shaft. A flange on the wheel end of
the shaft is used to attach the wheel.
semifloating axles are used to drive the vehicle, the axle shafts push on the
shaft bearings as they rotate. This places a driving force on the axle housing,
springs, and vehicle chassis moving the vehicle forward. The axle shafts takes
bending stresses associated with turning corners and curves, skidding, bent or
wobbling wheels, as well as the weight of the vehicle. In the semifloating axle
arrangement, if the axle shaft breaks, the driving wheel comes away from or out
of the axle housing.
Three-Quarter Floating Axle
wheel bearing on a three-quarter floating axle is on the outside of the axle
housing instead of inside the housing as in the semifloating axle. The wheel
hubs are bolted to the end of the axle shaft and are supported by the bearing.
In this arrangement, the axle shaft does not support the weight of the vehicle.
It is transferred through the wheel hub and bearing to the axle housing.
Three-quarter floating axles are found on older vehicles and some trucks.
Full-Floating Axle Shafts
heavy commercial vehicles use a full-floating axle shaft to accommodate the
higher vehicle loads. This design is similar to the three-quarter floating axle
except that two bearings rather than one are used to support the wheel hub.
These are pressed over the outside of the axle housing and carry all of the
stresses caused by the torque loading and turning. The wheel hubs are bolted to
flanges on the outer end of each axle shaft.
operation, the axle shaft transmits only the driving torque. The driving torque
from the axle shaft rotates the axle flange, wheel hub, and rear driving wheel.
The wheel hub forces its bearings against the axle housing to move the vehicle.
The stresses caused by turning, skidding, and bent or wobbling wheels are taken
by the axle housing through the wheel bearings. If a full-floating axle shaft
should break, it can be removed from the axle housing. Because the rear wheels
rotate around the rear axle housing the disabled vehicle can be towed to a
service area for replacement of the axle shaft. This is considered by many
technicians to be an advantage of the full-floating axle design.
Independently Suspended Axles
type of rear driving axle system is found mostly on European automobiles. The
driving axles are usually open instead of being enclosed in an axle housing.
two most common suspended rear driving axles are DeDion axle system and the
swing axle system.
DeDION AXLE SYSTEM The DeDion axle system resembles a driveline. The
driveline axle resembles a drive shaft, with U-joints at each end of the axles.
A slip joint is attached to the inboard, or innermost, U-joint. The outboard, or
outermost, U-joint is connected to the driving wheel. This allows the driving
axle to move up and down as it rotates.
SWING AXLE SYSTEM On automobiles with swing axles, the driving axles can be
open or enclosed. An axle fits into the differential by way of a ball-and-socket
system that allows the axle to pivot up and down. As the axle pivots, the
driving wheel swings up and down. This system best describes the drive axles of
a front-wheel-drive vehicle.
Axle Shaft Bearings
axle shaft bearing supports the vehicle's weight and reduces rotational
friction. In an axle mount, radial and thrust loads are always present on the
axle shaft bearing when the vehicle is moving. Radial bearing loads act at 90
degrees to the axle shaft's center of axis. Radial loading is always present
whether or not the vehicle is moving.
Thrust loading acts on the axle bearing parallel with the center of axis. It
is present on the driving wheels, axle shafts, and axle bearings when the
vehicle turns corners or curves.
are three designs of axle shaft bearings used in semifloating axles.
bearing load of primary concern is axle shaft end thrust. when a vehicle moves
around a corner, centrifugal force acts on the vehicle body, causing it to lean
to the outside of the curve. The vehicle's chassis does not lean because of the
tires' contact with the road's surface. As the body leans outward, a thrust load
is placed on the axle shaft and axle bearing. Each type of axle shaft bearing
handles axle shaft end thrust differently.
Normally, the way the axles are held in the housing is quite obvious after the
rear wheels and brake assemblies have been removed. If the axle shaft is held in
by a retainer and three or four bolts, it is not necessary to remove the
differential rover to remove the axle. Most ball- and tapered-roller bearing
supported axle shafts are retained in this manner. To remove the axle, remove
the bolts that hold the retainer to the backing plate, then pull the axle out.
Normally, the axle shaft slides out without the aid of a puller. Sometimes a
puller is required.
tapered-roller bearing supported axle shaft does not use a retainer to secure
it. Rather, a C-washer is used to retain the axle shaft. This C-washer is
located inside the differential, and the differential cover must be removed to
gain access to it. To remove this type of axle, first remove the wheel, brake
drum, and differential cover. Then, remove the differential pinion shaft
retaining bolt and differential pinion shaft. Now push the axle shaft in and
remove the C-washer. The axle can now be pulled out of the bearing.
bearings are lubricated with grease packed in the bearing at the factory. An
inner seal, designed to keep the gear oil from the bearing, rides on the axle
shaft just in front of the retaining ring. This type of bearing also has an
outer seal to prevent grease from spraying onto the rear brakes. Ball-type axle
bearings are pressed on and off the axle shaft. The retainer ring is made of
soft metal and is pressed onto the shaft against the wheel bearing. Never use a
torch to remove the ring. Rather, drill into it or notch it in several places
with a cold chisel to break the seal. The ring can then be slid off the shaft
easily. Heat should not be used to remove the ring because it can take the
temper out of the shaft and thereby weaken it. Likewise, a torch should never be
used to remove a bearing from an axle shaft.
Roller axle bearings are lubricated by the gear oil in the axle housing.
Therefore, only a seal to protect the brakes is necessary with these bearings.
These bearings are typically pressed into the axle housing and not onto the
axle. To remove them, the axle must first be removed and then the bearing pulled
out of the housing. With the axle out, inspect the area where it rides on the
bearing for pits or scores. If any are present, replace the axle.
Tapered-roller axle bearings are not lubricated by gear oil. They are sealed and
lubricated with wheel grease. This type of bearing uses two seals and must be
pressed on and off the axle shaft using a press. After the bearing is pressed
onto the shaft, it must be packed with wheel bearing grease. After packing the
bearing, install the axle in the housing. Shaft end play must be checked. Use a
dial indicator and adjust the end play to the specifications given in the
service manual. If the end play is not within specifications, change the size of
the bearing shim.
installation of new axle shaft seals is recommended whenever the axle shafts
have been removed. Some axle seals are identified as being either right or left
side. When installing new seals, make sure to install the correct seal in each
side. Check the seals or makings of right or left or for color coding.