4WD How-to: Beam Front Axle Wheel Alignment Made
Wheel alignment is a basic Jeep or 4x4
truck maintenance need. Suspension modifications, normal chassis and steering linkage wear, off-pavement
trail pounding and the use of oversized tires can each impact the front wheel
Also see the beam axle wheel alignment 'how-to' HD video, click
The popular, time‐honored Jeep off‐pavement trail runners have a
beam (“solid”) live front axle. More civilized Jeep models with independent front suspension (IFS) include
the KJ Liberty, 2005‐up Grand Cherokee and the Commander. Each of these Jeep 4WD vehicles has a hypoid, solid rear axle
Since most trail vehicles upgrade to
expensive, oversized traction tires, premature wear of tires is
always a concern. Periodic tire rotation and
proper wheel alignment are basic safeguards to
prevent abnormal tire wear.
The less complicated Jeep 4WD beam front axle is not
just strong and durable. It also has fewer
maintenance requirements. Camber is set at the factory with
the jig‐welding of the beam. Caster is adjustable for
the slight sagging of aged springs or the settling
of spring or link arm bushings. For all Jeep vehicles,
a common alignment need is toe‐set.
Caution: Wheel alignment is never a substitute
for replacing worn or damaged parts. A bent steering
knuckle, tie‐rod or axle beam needs replacement. Straightening trail damaged
steering linkage or a bent knuckle is not safe
Wheel alignment at the modern shop most
often includes four‐wheel “thrust” inspection and a
check of the caster, camber and toe-set. Some shops
can perform a true “four‐wheel alignment,” but this
is generally not necessary on the trail oriented Jeep
4WD models unless an aftermarket
lift kit has adjustable rear wheel link arms or there is suspicion of a
bent rear axle or frame damage.
Thrust alignment does take rear axle
shift, worn springs, bad bushings or a bent frame into
account. A shop that performs either four-wheel or
thrust alignment can handle any vehicle with a
solid, hypoid rear axle system.
To push the vehicle forward in a straight line,
rear axle thrust must be perpendicular to the
centerline of the frame. When thrust is correct, a front
wheel alignment assures precise steering and a
normal steering wheel position.
On turns, the inside wheel has a
tighter turning angle than the outside wheel. This is
“Ackerman steer,” the result of the steering knuckle’s
kingpin inclination, caster angle and the steering axis
inclination (‘SAI’). Each of these variables
affect steering and the vehicle’s behavior when
Caster is often adjustable.
When SAI is incorrect, however, the most common cause is a damaged
steering knuckle or bent spindle.
Note: If you have no reason
to suspect knuckle or spindle damage, checking the SAI is of
lesser importance. If your Jeep rear axle is square
with the frame and not bent, there is not a call for
thrustalignment. At the 'Workshop' areas of this
website/magazine, I share information on how to set up a lift kit and adjust link arms to assure proper thrust and
axle alignment with the frame.
Toe set is the most common measurement
associated with front wheel alignment. Normal
chassis and linkage wear, plus the characteristic
pounding that 4x4s get on rough trails, make toe-set
a periodic maintenance chore.
Toe-in is the precise angle of the front wheels
when the steering and wheels aim straight ahead.
While parallel front wheels would seem ideal, the front
wheels seldom callfor zero-degrees of toe set. The basic wheel alignment is
Due to the
thrust loads of the vehicle moving forward (especially with oversized tires!) and
the slight movement of steering joints under load, toe
is actually set so that tires “toe-in” slightly when static.
Toe-in is measurable at the forward side of the front
The tires’ design dictates toe-in
requirements. Bias-ply tires have a tendency to thrust
outward under load. The classic Willys or Jeep CJ with
OEM type, bias‐ply tires should follow factory
alignment specifications. That toe-in might be in the
1/16”‐3/16” range, typically a 1/8” setting.
If using modern radial tires, toe-in should be
near zero, something like 1/32” for stock tires.
(Modern alignment racks measure in tenths of
a degree, not inches.) The higher-end alignment
equipment can check toe-set with projectors and
electronic beams. As you will see in this technical
article, toe-in can also be checked with basic
With the chassis weighted and the front
tires pointing straight ahead, each tire should
stand nearly vertical. Viewed
from the front of the vehicle, camber degrees are the tilt of the tires, inward
or outward, from a vertical centerline. If the top of
the tire tilts outward, camber is “positive.” If the top
of the tire tilts inward, camber is
Jeep beam type axles with leaf springs or
link arms have fixed camber. As the vehicle’s frame
and body lean on corners, the axle stays parallel
with the ground. With this design, there is no
provision for adjusting the camber.* Unless the axle
housing is bent, or worn ball-joints cause knuckle
sagging, the axle maintains its original camber
*Note: Camber can be corrected with aftermarket
offset ball-joints or eccentric ball stud seats. There
is, however, no OEM provision for adjusting camber on a solid beam
Jeep 4WD front axle.
By contrast, each front wheel on an
IFS suspension, like the Jeep 4WD Liberty or late Grand Cherokee
models, moves up or down independently. Short (upper) and long (lower) control arm
“SLA” suspension compensates for body/frame lean
As the vehicle corners, the body/frame
rolls, causing the outside wheels to compress the
springs. This moves the wheels upward into the
fender wells. The unloading (inside) wheels drop as the
body rolls outward. A functioning sway bar
helps minimize this body/frame roll.
On SLA suspension like the Jeep Liberty 4WD, late
Grand Cherokee or Commander, tire track width
remains relatively constant during this process. The arc
of wheel travel is precisely engineered for
maximum control and long tire life.
Solid, beam front axle Jeep 4WD
vehicles have a simpler approach. As the frame/body rolls on
turns, the axle, wheels and tires stay parallel to
the ground—unless we’re rock
crawling with wheels in the air! The
outside leaf springs or coil springs compress, as the suspension allows for this roll.
As the outside wheel compresses the
suspension, the sway bar makes the vehicle squat—pulling
the chassis downward, lessening the body/frame
roll and lowering the center of gravity. The sway bar
has a clear purpose, especially on the highway
and when cornering at speed.
Caution: If your Jeep
4WD has a factory sway bar, it should be connected for highway driving! Sway bar disconnects allow more axle
articulation off-pavement, which is their intended use. On-highway, the sway bar is a valuable
Caster plays an
important role in vehicle handling. Caster is the tilt of the kingpin or
ball-joint centerlines when viewed from the side. Imagine
a line drawn through the center of the upper and lower
ball joints (or the kingpin/knuckle bearings on a vintage Willys or
Kaiser era Jeep 4WD). That is the kingpin centerline. The forward
or rearward tilt of this centerline, measured
in degrees, is the caster angle.
The kingpin or ball-joint centerline
tilts inward as well, but this is not caster. Inward tilt
is kingpin inclination, a measurement that affects
the steering axis inclination (SAI). When caster
and camber are within specification, SAI should be
as well. If not, suspect a bent or defective spindle
or steering knuckle.
Typical front suspension calls for
positive degrees of caster. Positive caster means that
the upper end of the kingpin or ball‐joint centerline
tilts toward the rear of the vehicle. Caster has a
very important function: helping
the front wheels come back to center after
When there is too little caster angle, the
most notable symptom is the need to actually steer the vehicle back to center as the Jeep exits a turn. Correct caster
settings also help steer the vehicle straight ahead, helping to
overcome the effects of the road crown. (Camber plays a role
Caster angle helps prevent pull and reduces
the risk of kingpin or ball-shimmy. Some
Jeep owners talk of this phenomenon as the
“death wobble” frequently associated with short arm,
link-and-coil suspension lift kits that reduce caster
For the Jeep vehicle with a beam front axle,
toe-in is often the only adjustment needed if: 1) the
frame and axle beam are straight, 2) the springs
set evenly, 3) the knuckles and joints are in good
condition, and 4) caster and camber meet
Whether setting up a modified suspension
or simply restoring your Jeep vehicle’s steering,
always consider caster, camber and toe-set. Changing
the spring length or arch, changing the link arms,
and other measures involved with lifting the
chassis—each requires an alignment check and
Every Jeep owner wants improved
steering control, safe handling and maximum tire
life. Performing your own wheel alignment and
steering or suspension diagnostics can save money and
bring a valuable resource into your shop or home
‘SPC’ Makes Wheel Alignment Easy!
With a beam axle, it is possible to do
on the spot toe-set adjustments. Alongside the trail, I’ve
set basic toe with nothing more than a tape
measure and hand wrenches. For home use, a simple
toe‐bar and tire centerline scribe can be purchased
through automotive tool suppliers.
For an affordable, far more thorough
approach, there is Specialty Products Company’s FasTrax® alignment equipment. The FasTrax® 91025 ‘Off‐Road’ alignment gauge kit provides a portable,
fast and accurate way to measure toe-set, caster
and camber on vehicles with larger tire packages.
As a budding mechanic in the ‘sixties, I
was fascinated by the early wheel alignment
equipment that was still in service. For decades, both
before and after WWII, magnetic and clamp-on caster
and camber gauges were common. These gauges, with a
simple toe-set bar and turn plates, met the
garage, dealership and body shop standards of that era. In the
right hands, these tools provided accurate wheel
service for trucks, cars and, yes, the vintage Jeep 4WD
I ran a modern Hunter alignment rack at a
truck dealership in the early 1980s. From 1999-2004,
I instructed automotive/diesel technology at the adult vocational education
level, involving more contemporary wheel alignment equipment. Today, $40K alignment systems
with electronically controlled projection heads, drive-on
ramp racks, degree’d turn plates and computer data
stations are common at alignment shops.
Clearly, modern electronic
equipment offers pinpoint accuracy. For a beam axle Jeep 4WD that often plies backcountry trails,
however, simpler equipment can do a reasonably accurate, far less costly
job! SPC’s portable equipment, at 1% the cost of a high-end alignment system, targets smaller automotive
shops, home garages, fleet operators and racing teams. Large-tire Jeep
4WDs are another niche. The SPC Model 91025 Off-Road wheel alignment system aims at off-road vehicles with oversized
wheels and tires.
The portable SPC 91025 package is an accurate
way to check wheel alignment, including camber,
caster and toe-set (with the toe-arms shown here). For
large tires, this is the kit. As an added benefit,
the equipment also works well as a quick diagnostic
For safe handling, minimizing tire
wear or customer satisfaction, this fast,
accurate alignment equipment demands
attention! Four-wheelers who pound around
on rocky trails, or the 4WD shop
that regularly installs lift kits, oversized wheels and
big tires, will value SPC equipment. Used properly, this is
a practical alternative to expensive alignment shop sublets.
As you will see, it also makes a useful troubleshooting tool!
1: To demonstrate a home-like setting, I
parked the XJ Cherokee on a recently poured
driveway slab. The FasTrax® 91025
comes with a floor calibrated base. Since the aim is to read angles
on a bubble level gauge, the level must be parallel
to the floor at each wheel. Here, I set a level on
the slab to get a sense for the floor’s level.
(The gauges will work on an uneven surface.) Begin the
alignment with the front wheels pointed straight
2: The use of sheet plastic beneath each tire is
a budget conscious alternative to turn plates. (If
you can afford turn plates, get them!) Plastic
reduces friction while turning the wheels
left-straight-right. Set FasTrax® base just
outboard the plastic and square with the tire’s face. Level the bubble to “0” on
the camber scale.
3: The two arms that come with the 91025
Off‐Road kit are for toe-set. I place them on
the gauge assembly before mounting the fixture on
the wheel. The 3‐point fixture clamps internally, tightened
with a rack gear and knob system on the fixture. American Racing wheels have
spot-on machining, which makes it easy to center
the gauge fixture and know that the gauge sets
4: When mounting the 3‐arm fixture, a
straight-edged spirit level helps align the gauge vertically.
This assures accuracy, as the gauge is now on
planevertically and horizontally. The first
measurement, with the wheels pointed precisely
straightahead, is camber. This is a beam axle
in good condition; camber should be a
non-issue. I quickly find this not to be the case,
5: Minus 3‐degrees (negative) camber! The
factory setting is minus 0.25-degrees with a
range or tolerance of 0.75-degrees negative to
0.5-degrees positive. This is the right side wheel, which tolerates
a bit of extra camber; however, there's
an extra 2.25-degrees negative. The gauge,
calibrated with the ground, reveals the negative
camber.Some jump to the conclusion that this means a bent
axle housing, but there are other possibilities as
6: Five minutes into the process, and the SPC
alignmentgauge serves as a precise
diagnostic tool for front end troubles! The excess
negative camber reflects a tilting steering knuckle.
This could be caused by a bent axle housing, but
the history of this vehicle does not suggest that kind
of trouble. As the Dana beam axles do run to the limit
of tolerance, sometimes even exceeding it, some
of this error could be inherent to the axle
Considering the XJ Cherokee’s 122K
miles and the use of large tires with shallower wheel backspacing
than stock, there is plenty of loading on the knuckle
ball joints. These are the original joints. If loose,
the natural slant of the knuckle will be
negative degrees, just like the reading found here.
So, before scrapping out an axle housing (although
a Dana 44 upgrade would be nice!), I will jack up each side
of the axle beam and check the ball joints for wear or
looseness.For the record, this vehicle steers
quite nicely, without signs of wobble…Given the lack of symptoms,
the SPC alignment gauge has proven useful as a preventive maintenance
7: Accurately checking caster without turn
plates does require innovation! The system calls
for turning the wheels 15 degrees each way
from center (straight ahead) during caster check. Opting
for the “plastic bag” approach, I placed
the straight edge (on ground) parallel with the
tire. Then I placed a protractor, set at fifteen
degrees, square with the straight edge. The idea is to
provide an accurate reference line.
8: I fired the engine to apply
power steering and turn the wheels. At the right side
of the vehicle, the turn was right,
to 15-degrees. Here, the alignment gauge is parallel with the
15-degree position at the yellow protractor. In
that position, set the bubble level on the SPC gauge to a precise
“0” along the caster scale.
9: Now turn the front wheels left to an
angle 15 degrees left of the straight ahead
position…At this point, the right wheel’s caster will read
in degrees along the caster scale of the bubble
10: The bubble is very clearly at
7.5-degrees positive caster. (Zoom-in for detail!)
This measurement is excellent. Factory preferred
caster is 7.0-degrees positive. Range is 5.25-degrees
positive to 8.5‐degrees positive. Caster
provides the desired return‐to‐center, and this XJ
Cherokee has been easy to drive and steer…Next, straighten
the steering to center (straight ahead). Move the
gaugeassembly to the left front wheel.
11: At the left front wheel, the gauge is
set flatly on the ground, just outboard of the wheel/tire. Zero the bubble gauge on
the Fastrax® 91025 gauge. Carefully raise the
gauge into position and mount it on the wheel rim. Handle the fixture
as you would a precision instrument. Do not disturb the bubble gauge
when clamping the assembly onto the wheel.
12: The gauge mounts squarely,
shouldered evenly against the wheel rim. Avoid clamping
the fixture at rim sections with wheel weights
or abrasions that might distort the angle. I again use the
straight-edgespirit level to align the fixture vertically. Once the fixture is squarely mounted
to the wheel, you can read camber on the
13: Read the left side camber measurement.
(You can zoom-in for detail.) This side reads nearly
2.5-degrees negative camber, well beyond the
OEM limits of 0.75-degrees negative.
Note: At 20,000-plus miles on these Toyo tires, wear
is uniform and nominal. Tire rotation at 5K‐7K
miles has minimized wear. Despite the poor
camber readings, the vehicle steers well. This camber
check has exposed a vital concern, however. While a bent
axle housing or knuckle can cause negative
camber, there is no evidence to support that kind of abuse. The
likely culprit is worn ball joints at the steering knuckles,
which would require attention. This kind of discovery quickly pays for the FasTrax® tool!
14: Caster can now be checked on the left
side. Wheels pointed straight ahead, the straight edge
is set parallel to the tire. Once again, the
protractor provides the line for 15 degrees of left turn
Note: Degree'd, floating turn
plates would simplify this part of the alignment, also eliminating the need for plastic sheets under the
tires. SPC does sell portable turn plates. Used plates can sometimes be found at auctions
or on Ebay!
15: Protractor set to 15-degrees left of
the straight ahead wheel position, turn wheels
until the bubble gauge is exactly parallel to the
15-degree line of the protractor.
Note: Again, turn plates would be helpful. Plates have
detailed degree marks and a pointer. They allow the front
wheels and tires to “float,” relieving thrust pressure and
allowing easy left-to-right turning of the wheels. On turn
plates, wheels can usually be turned left and right by hand, gripping
the tire without using the steering wheel. (Make sure the steering wheel
is unlocked!) SPC offers turn plates. Consider them!
16: Once again, turn the wheels out 15
degrees. (This is the left/driver’s side, so turn left.) At
the turned out position, move the bubble gauge to
“0” on the caster scale.
17: Here is the left front wheel turned outward
to the 15 degree point. Note that the bubble
gauge has been set to read “0” on the “Caster Sweep”
15-degree scale. The gauge is very clear and
responsive. I am confident that for Jeep 4WD
vehicles, especially those with a beam axle, this is a
reliable approach. In addition to alignment, the
tool demystifies front end, steering and axle
18: Now the final reading for caster. With
the front wheels turned 15 degrees right, the
caster sweep measurement is exactly 7-degrees
positive caster. The caster at each side reads well within
specification.Factory allowance is a maximum
right-to-left “difference” of 1.25 degrees.
Actual caster measurements are within 0.5 degrees
of each other. This is optimal.
19: Reading is 7-degrees positive caster at the
left front wheel. With these figures, steering is safe
and positive with optimal return to center feel. Caster angle
also dictates the driveline pinion angle. On vintage Jeep
4WD vehicles with single Cardan U-joints, front
end caster is less. This reduces the angle of the front
Note: Earlier Jeep beam axles call for 4‐degrees
positive caster. Chart below depicts a late model
Wrangler with an OEM, double Cardan (CV) joint at the transfer
case end of the front driveshaft. Note the use of more caster, which
is desirable for vehicle handling and tighter steering angles.
Factory Front Wheel
Note: I use
Jeep TJ Wrangler as an example here, a popular and
newer Jeep 4x4 with a beam axle. See your model's Jeep workshop manual for
PREFERRED CASTER: + 7.0° ±1.0°
CAMBER (fixed angle): 0.25° Negative ± 0.63°
TOTAL TOE-IN: 0.15° (each front wheel) ±0.06°
MAX RT/LT DIFFERENCE:
The Rear Axle has preferred OEM alignment specifications, also measurable
with the SPC FasTrax®
CASTER: Not Applicable. The only concern is
pinion angle for U-joint alignment.
CAMBER: –0.25° with 0° to –.50° Allowable
TOTAL TOE-IN: 0.25° with 0° to 0.5° Allowable
THRUST ANGLE 0° ± 0.25°
20: For setting toe-in, turn front wheels
directly back to straight ahead. The two wing arms on
the 91025 system have slots for various diameter
tires. Designed for off‐road vehicles, there are slots
that easily match the oversized, 33” tires on the XJ Cherokee.
I like to measure toe as close to the
horizontal centerline of the tires as practical. Make sure
that the tape can cross to the opposite side
without bowing or hitting obstructions. Keep tape
parallel to the ground and just outboard of tire
21: For toe‐set, the tape goes straight across
to the passenger side tire. Measure width at the
rear and front of the tires. The difference is toe.
Shorter at the front than rear is “toe-in.” Shorter at
the rear of the tires is “toe-out.” Stock radial tires
call for “0-degrees” toe on this XJ Cherokee. With
large tires, wide rims, shallower backspacing and lots
of unsprung weight mass, these tires will
naturally toe outward as the vehicle moves forward. From experience,
I set a toe-in of 3/32” to compensate.
22: Some use two 91025 kits and measure
between the four toe arms. With one kit, I measure
toe from the left side arms to either
a scribed centerline at the right side tire or
a common tread pattern point. Here, a
reference point is established at the rear of the right
front tire. Remove tape slack but do not pull hard.
The extended toe arms will bow if you apply too
much pressure. For accuracy, match the tape
tension during the front and rear measurement checks.
23: Some place the toe arms near the
floor. I set the FasTrax® toe arms
near the middle of the tire as shown. The tape parallel with the ground,
reach across to the opposite tire. Pick a matching
tire tread pattern point at the front of the tire;
measure the distance. In this case, the front measurement
is slightly shorter as desired. This indicates toe-in instead of
Note: Picking a matching tread point can be tricky.
The tape should be as level as possible. Make sure the
tread reference patterns are identical, front and
24: At the front side of the
front tires, the measurement is 72-1/8”. At the rear, the measurement to the same tread pattern point is slightly under 72-1/4”. The difference is 3/32”—shorter at the front side of the front tires. Front measurement being shorter, this wheel alignment has “toe-in.” Slight toe-in will work well for the tire size and vehicle’s weight distribution; the heavy winch and bumper place
additional load on the front axle.
When aligning the front wheels, make
sure the steering wheel aligns with the steering gear’s
center point. If the steering wheel centers with the steering gear,
do not remove and reposition
wheel to center it during a wheel alignment!
Instead, point the front wheels straight
ahead. After adjusting toe, center the steering wheel
by adjusting the short tie rod or draglink. Road test
and readjust again if necessary. Do not change the front
wheel toe setting in the process. Re-check toe-in if
Note: The only Jeep vehicles that require
repositioning the steering wheel are early model Willys
trucks equipped with a non-adjustable, fixed length
draglink. On these models, the steering gear must
still be very close to its center point (the over-center
high point) when the front wheels point straight
Adjusted properly, the steering wheel should
be on center with the front wheels steering
straight ahead. The steering gear should be at its
over-center high point (midway between left and
right turning extremes) when the front wheels
point straight ahead. By design, this will provide the
least amount of steering backlash or play when
the vehicle steers straight down the road.
Sierra Stomper Dan Wilson took
his 1988 XJ Cherokee on trail
recently. Portable wheel alignment gauges
would be a valuable tool at Dan’s home shop! (Photo courtesy of Dan Wilson. All other photography by Moses
FasTrax® 91015 Caster-Camber-Toe Gauge
The Specialty Products Company’s Model
91025 alignment kit works very well! Portable and light in weight, the gauge's quality construction maintains calibration and
tolerance. Alignment chores are easy with this kit. The design incorporates proven features like a bubble caster and
A precisely machined, gear
drive clamping fixture, attractively
anodized, should deliver reliable service over time. SPC’s 91025 FasTrax® kit for
Off‐Road vehicles is an optimal investment for the aftermarket suspension installation shop or any serious racer/trail runner who wants
maximum handling and performance from a Jeep 4WD. This is a useful troubleshooting tool as well, capable of
quickly revealing suspension, live beam axle and steering system damage...
Unless you have the shop space and an unlimited budget for
electronic alignment equipment with a four-wheel alignment rack, consider the FasTrax® 91025 a cost-effective, sensible alternative. Accurate,
portable and designed to set up quickly on any flat surface, the
Specialty Products Company’s FasTrax® 91025 should be
a fixture at the garage and pit area of every off-road race
Serious trail runners and any Jeep
owner who does his or her own service work will find this tool valuable.
Save tires, save time and diagnose trouble at the earliest point with this versatile tool. For the fleet truck
shop with a preventive maintenance and service program, the FasTrax® could pay for
itself in a week!
specializes in niche suspension and steering parts for Jeep 4WDs,
popular trucks, SUVs, passenger cars and off-road racing vehicles. Products include offset ball-joints
and eccentric seats for adjusting caster and camber. The catalog features unique alignment shims and eccentric bolts for
adjusting link arms, plus coil spring spacers and bushings.
Supplying a variety of specialty tools
and parts, SPC also heads up the “Light Racing” parts program.
Popular among rock crawlers and professional desert racers, Light Racing
offers special hardware and suspension components.
‘SPC’ has a demonstration video
avaiable for the 91000-series FasTrax® tools in operation. Click on this link to see the video:
In business since 1972,
Specialty Products Company has a full product line for Jeep
4WD owners and 4X4 specialty shops. You can download the SPC catalogs or get more information at: