4WHEELOFFROAD.COM 4-WHEEL & OFF-ROADOCTOBER 2019 29
CHRYSLER/AMC
CHRYSLER 8^1 ⁄ 4
Identification: Oval-shaped 10-bolt dif-
ferential cover with a flat section at the
bottom, 11^3 ⁄ 8 inches wide, rubber fill plug.
Specs: 81 ⁄ 4 -inch ring gear, 11^3 ⁄ 8 inches
wide, 27- or 29-spline semifloating axles,
2.73-4.88 gears.
Found In: Rear of 1991-2001 Jeep Chero -
kees and 2003-2007 Jeep Liberties; some
early Dodge Dakotas and vans.
The Good: Specific to Cherokees (which
is the most prevalent 8^1 ⁄ 4 platform) the
biggest thing an 8^1 ⁄ 4 has going for it is
that it’s not a Dana 35. While the 27-spline
versions are only marginally stronger
than the Dana 35, the 1996^1 ⁄ 2 and later
29 -spline versions make the axle roughly
equivalent to a Dana 44.
The Bad: Though decent, the Chrysler 8^1 ⁄ 4
is really a light-duty axle and is not up to
lot s of abuse. Gear ratios and af termarket
support are somewhat limited compared to
other axles.CHRYSLER 8^1 ⁄ 4AMC 20
Identification: Perfectly round differen-
tial cover with 12 bolts, about the size of a
basketball cut in half.
Specs: 87 ⁄ 8 -inch-diameter ring gear,
29-spline semifloating (often two-piece)
axleshafts, 2.73-4.88 gears.
Found In: Rear of 1976 -1986 Jeep CJ -5s
and CJ-7s, and fullsize Jeeps of the same era.
The Good: Though often maligned, the
AMC 20 actually boasts a stronger ring-
and-pinion than a Dana 44, and most of its
shortcomings can be addressed with some
fairly simple modifications. The biggest
attribute that an AMC 20 has for a builder
is that it’s already present; it’s not a good
swap candidate into another application in
most cases.
The Bad: The stock two-piece axleshafts
in CJs are a break waiting to happen if they
haven’t already. The CJ centersection cast-
ings and axletubes are fairly thin, making
them easy to bend. Just about any AMC 20
is going to take some money and time to
make capable of surviving moderate abuse.
Notes: Some of the FSJ AMC 20 applica-
tions came with one-piece axles, eliminat-
ing the need to upgrade them, and the
FSJ housings are more rugged than the CJ
versions. AMC 20s were also used in quite
a few car applications, so aftermarket
support and upgrades remain surprisingly
strong for an axle with a relatively limited
production run.AMC 20ting any money in one of these axles when
14-bolts are so cheap and plentiful. These
axles are also getting harder to find now
that square-body Chevys aren’t as preva-
lent in wrecking yards as they once were.
Notes: Like the GM 10 - bolt , the truck
12-bolt has almost nothing in common
with the car version of the 12-bolt. They
are a mild upgrade to a 10-bolt, but we
wouldn’t go through the hassle of swap-
ping one in the place of a 10-bolt unless
the axle was free. Still, these would be a
viable option if going to eight-lug wheels
was out of the question.
GM 14-BOLT
Identification: Fairly prominent octago-
nal differential cover with 14 bolts, full-
floating design, single or dual wheel.
Specs: 101 ⁄ 2 -inch ring gear, 30-spline axles,
3.21-5.38 gears, full-floating axles, eight-lug.
Found In: Rear of various GM^3 ⁄ 4 -ton,
1-to n , a n d 1^1 ⁄ 4 -ton trucks, vans, and SUVs
from 1973 to today.
The Good: Pretty much the gold stan-
dard of axle beef, there are few cheaper or
better choices for a serious axle upgrade
than the GM 14-bolt. Bulletproof right out
of the gate, a 14-bolt needs very little to
withstand big tires, big power, and big
abuse. With such a long production run and
widespread use, it’s hard not to trip over
multiple 14-bolts in any junkyard across
the country, and we’ve paid as little as $50
for one. Later-model axles even have disc
brakes.
The Bad: The large centersection of the
differential housing is a low-hanging shovel
that hurts ground clearance. The drum brake
versions are about 120 pounds heavier than
disc brake versions due to the heavier brake
assembly. Stock yokes are usually oddball
GM-specific U-joints and not standard Spicer
1310/1330/1350 stuff.
Notes: Don’t confuse the full-floating
14-bolt with the lighter-duty semifloating
axle with a 9^1 ⁄ 2 -inch ring gear of the same
name; they have almost nothing in com-
mon. When swapping one, consider an
axle shave kit because it can significantly
improve ground clearance.
GM 14-BOLT