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| Basic
Axle Information: |
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Semi-Floaters:
Most 1/2 ton and lighter vehicles are equipped with a "semi-floating"
rearend. In a semi-floating design, the wheel bolts directly
to a flange formed at the end of the axle shaft. A single
bearing supports the outer end of the shaft, which is located
just inside the housing end. Therefore, the axle shaft has
both forces acting; one has to support the weight of the
vehicle, two it has to turn the wheels to propel the vehicle.
Semi-floating rearends are usually less expensive to purchase
or build and lighter than full-floaters, but can be as strong
or stronger if you choose the right rearend and have it
built correctly.
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| Full-Floaters:
In applications like heavy duty 3/4 and 1 ton trucks, semi-floaters
are much less desirable because the heavier weight of the
vehicle combined with the twisting forces can cause semi-floater
shaft to bend or break. Obviously, having your rear wheel
pass you on the road can be somewhat unsettling. To prevent
this from happening, full-floaters use an axle housing with
a spindle formed at the end of the axle tube. The wheel
is bolted to a separate hub, which spins on two opposed,
tapered roller bearings. Since the weight of the vehicle
is supported by the spindle on the housing and not the axle
shaft, the shaft is only subjected to twisting forces form
the engine.
Full Floater Diagram
(Click To Enlarge)
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| Integral
Carrier Design:
Common
examples of integral carrier housings are: almost all Dana
axles, GM corporate axles and some ford axles, like the
8.8 or 10.25" full floaters found in F-Trucks. This
style of housing is easily recognized by a center casting
with tubing pressed in from either side. The tubes are pressed
very tightly into the casting, and are plug welded so they
will not twist or pull out. There are bearings in the end
of the housing to support the wheels, and this type of housing
is commonly used for both full-floating or semi-floating
axles. This design can also be recognized by the removable
cover used for gear inspection and installation.
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Removable
Carrier Design:
The
Ford 9-inch and Toyota rearends are good examples of the
removable carrier design. These rearends use a housing made
from several pieces of stamped steel that have been welded
together as a single unit. The gears are contained in a
bolt in center casting commonly referred to as a "third
member." The third member is inserted into the housing
from the driveshaft side of the rearend, and is held by
a circle of bolts. Drag racers enjoy this style of rearend
because they can set up different gear ratios in multiple
third members and quickly change ratios between rounds.
This type of rearend usually has no removable cover; in
order to inspect the gears, you have to completely remove
the axle shafts and drop the third member from the main
housing.
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| Reverse-Cut
vs. Standard-Cut:
Often
mistakenly referred to as "reverse rotation,"
the term "reverse-cut" is perhaps the single most
misunterstood term by four wheelers and even many in the
axle business. Areverse cut housing is not just like a standard
cut housing turned upside down. It is a specially designed
housing for fount driving axles. Contrary to popular belief,
it does not turn backwards or in reverse. The term "reverse-cut"
actually refers to the direcrtion of the spiral cut in the
ring gear.
In
a reverse cut axle, the spiral on the ring gear is opposite
form a standard -cut ring gear. The idea behind reverse
cut is to strengthen the operation of the gear when it is
used for a front axle application.
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the early day of four wheel drive, the front axle used the
same gears and housing as an ordinary rearend. This was done
for economic reasons, since the components were already in
mass production. They simply added the necessary parts to
enable steering. However, all ring and pinion gears are cut
in such a way that they are inherently stronger when pushing
the cehicle in the forward direction and weaker when driving
in reverse. That means that a standard cut (rearend style)
gear, when used in the front, must push on the weaker side
of the gear to move the vehicle in a forward direction.
This
practive continued until the late 1970s, when Dana designed
a new axle that would be stronger for front axle use and
also provide better driveline angles for the shorter fornt
driveshafts then being used in new trucks. The reverse cut
housing and reverse cut gear set can be identified by the
pinion gear, which is located abve the centerline of the
axle shaft. Therefore, standard cut gears are always strongest
when used in rear axles and reverse cut gears are stonger
when used in front axles.
Reverse
cut axles have also become popular for lifted short wheelbase
vehicles like Jeeps, early Broncos and Land Cruisers. The
reason is because the higher pinion location greatly reduces
rear driveshaft angles. However, not all reverse cut axles
are strong enough for use as a rearend. The cut of the gear
that makes them stronger for the front axle use also makes
them somewhat weaker for the rear axle use. The best and
most popular reverse cut axle for rearend use is the Dana
60, a good choice because of its larg ring gear diameter,
tooth strength, ability to accept 35 spline axle shafts
and wide selection of ratios and differentials.
Two
other reverse cut axle are the Dana 44 and a new Ford 8.8"
reverse cut. The Dana 44 makes an excellent front axle,
but just isn't strong enough for rear axle use. The Ford
8.8", reverse cut rearend (new from Currie Enterprises)
has a slightly larger ring gear than the 8.5" of the
Dana 44 but is not nearly as strong as the Dana 60, which
has a 9.75" ring gear. The new 8.8" uses a special
third member that bolts into a removable carrier Ford 9
inch housing and its somethimes mistakenly referred to as
a reverse cut Ford 9 inch. Both the Dana 44 and the ford
8.8" can accept a maximum of a 30 to 31 spline axle
shaft.
The
bottom line is that reverse cut gears (front axle style)
and axle assemblies are inherently stonger for fornt axle
use because of the way the gear mesh when moving the vehicle
forward direction. They also provide better driveline angles
because the pinion is located above the centerline of the
axle. The gear set used in each type of aaxle are not interchangeable.
Standard cut gears cannot be used in place of reverse cut
and vice versa. The housins are also not interchangeable.
However, differental cases, be open, limited slip or locker
are compatible with both styles, as long as the spline count
matches the axle shaft.
Back
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Information
Courtesy Of:
FourWheeler January 1999 |
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