4WHEELOFFROAD.COM 4-WHEEL & OFF-ROADNOVEMBER 2019 43
AXLE COMPONENTS & CONSIDERATIONS
-^ RING-AND-PINION: Dia m eter, hy p oid g ea r a n gle, high pinion or low pinio n
-^ CARRIER: Drop-in locker, full replacement case
-^ AXLESHAFTS: Material, spline count, diameter
-^ AXLETUBES: Diameter, thickness, trusses
-^ HOUSING ENDS: Full float o r semi float (rea r)
-^ HUBS: Hubs or drive slugs, bolts or studs to attach
-^ YOKE/FLANGE: Size, st ra ps o r U - b olt s
-^ U-JOINTS: Diameter, material
AXLE SURVIVAL FACTORS
- Horsepower
- Gearing
- Vehicle weight
- Terrain/traction
- Tire size
- Tire weight
- Wheel weight
axle. Automatic transmissions generally can cushion the rest of the
drivetrain, including axles, through the slip in the torque converter.
Ring-and-pinions tend to be damaged by shock loads from things
such as hopping and jumping. A xleshaf t s tend to succumb to
torque, twisting until they fail.
Ring-and-pinions larger in diameter are stronger as a result of
more contact area through tooth engagement (the same reason
an axleshaft with more splines is stronger than the same diameter
axleshaft with fewer). That larger ring gear also allows for a bigger
carrier, which is in turn stronger as well.
All of this is not to discount tire size as a factor. Certainly, a larger
tire places more leverage and stress on the axle assembly and,
in particular, the axleshafts. The weight of tires (and wheels) can
var y widely as well , and should be considered when comparing
products. For example, 37-inch-tall tires vary all the way from 68
pounds for all-terrains with two-ply sidewalls up to a whopping 94
pounds for the heaviest, Load Range E mud-terrain. Similarly, we
have seen 17-inch wheel s var y from 22 pounds all the way up to 37,
and those are both non-beadlock aluminum wheels. A lighter tire
and wheel combination will not only be easier on your axles but
also provide improved braking and acceleration. Things get com-
plicated on a vehicle used off-road though, since a tire that is too
light might be more susceptible to punctures than a tire with heavi-
er construction. All of which is a long way of saying, “It depends.”
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Aftermarket carriers tend to be
stronger than factory carriers,
with a spool being the strongest
(and least expensive) of all with no
moving parts. The only thing less
expensive than a spool is welding
the differential up, but even though
that’s cheap, it’s not a particularly
strong option. If it breaks, expect to
change not only the carrier but the
ring-and-pinion and bearings as well.2
This axleshaft broke right
where it enters the carrier. It
wasn’t subjected to high hor se -
power, but the tire was wedged
under a ledge and the 257:1 gear
reduction of the vehicle caused the
torque to overcome the a x leshaf t
in this situation.3
Twisted splines can occur over
time and are generally a func-
tion of large tires and low gearing
more than shock loads, which will
cause the axleshaft (or ring-and-
pinion) to break. Some of f- road
racers even use a paint pen toput a line down the axleshaft and
remove and inspect them periodi-
cally for twisting.4
Ford 9 - inch and GM 14 - bolt
axles have a third pinion bear-
ing in front of the pinion teeth. This
drastically reduces gear deflection
under shock loads and is one of the
reasons these axles are so strong
for off-road use.5
U-joint caps can work their way
loose in front axles as the yokes
stretch and deform. Using full-
circle snap rings prevents this from
happening, even with standard
U-joints. Adding chromoly U-joints
with larger trunions increases
strength even more.6
High-pinion or reverse-rotation
gearsets are stronger when
used in front axle applications
since the gears are meshing on the
drive side instead of the coast side.
For the same reason, these gears
are weaker when used in the rear.
They are sometimes still used in
the rear since they do benefit from
raising the driveline up above the
axle centerline.145
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