Part 3: Suspension & Wheel Alignment,
Driveline Upgrades and Exhaust
[Illustration courtesy of
Once the new suspension system is in place, final adjustments will be necessary. Even a
non-adjustable, fixed-length link arm system will require caster and toe-in checks. With adjustable link arms, the
possible adjustments also include axle and frame front-to-rear alignment, “thrust angle” and lateral alignment of
the axle assemblies. The axles must be true to each other and square with the frame. Front axle caster, rear axle
pinion angle, overall wheelbase length and the axle fore-and-aft positions are crucial.
While a capable installer can
bring these adjustments near their final settings, it is always essential to use a four-wheel alignment rack for
final checks and settings. Four-wheel alignment racks can confirm the square dimensions of the chassis and axle
an adjustable track bar, six adjustable link arms and an adjustable V-link Heim joint, the Full-Traction Suspension
4” lift 'Ultimate' system provides for fine tuning the suspension—or total chaos if not adjusted
properly! This installation provides an in-depth look
at the chassis, axle alignment and the tuning needs of a Jeep TJ Wrangler chassis.
Illus. 141: Rearward facing view
shows the relationship of the V-link, lower control/link arms and sway bar. Full-Traction Suspension’s rear
three-link system requires no frame or axle modifications. Improved ride and handling plus gains in off-pavement
articulation and wheel travel make this system unique. Its bolt-on status is both user-friendly and appealing to
installers who do not want a radically altered frame or axle housings.
Illus. 142: World renown, tuned
Bilstein 5100 gas-charged shock absorbers provide predictable highway handling and ample off-pavement traction.
Lower shock absorber is also a high-pressure gas charged type, the Full-Traction Suspension “M-Force” design.
M-Force shocks are built to FTS specifications to match the spring rates and handling expectations of users. Shock
absorbers play a large role in vehicle dynamics. Gas-charged shocks have specific rates and lengths of travel built
into their design.
Illus. 143: View forward shows
link arms adjusted for correct pinion angle on the front driveline. In doing so, bring axle caster close to
specification. This will be confirmed on the alignment rack shortly. I make a final check for driveline length,
axle position to the frame and spring/axle plumb lines. If necessary, use of string lines can help determine
“square,” wheelbase length and lateral alignment of the axle assemblies. Measuring from fixed points at the outer
axle housing and frame, determine the distances front-to-rear and diagonally in cross.
Note—If the rear axle was
left in the OE position while aligning the front axle, and if the front axle was in place while aligning the rear
axle, the axles should be close to square with each other and the frame. With adjustable link arms, extra steps
assure a square chassis and axle alignment. Final adjustments and tuning on the alignment rack will be much easier
if you take measurements during installation of the suspension system. Factory and aftermarket fixed-length arms
require few, if any, adjustments.
Illus. 144: This is the completed
front suspension. Note that the upper and lower link arms and the track bar are each adjustable in this
application. Fine tuning is possible—or utter chaos if these adjustments
are not correct. Wrong adjustments could alter the pinion
angle/caster, the lateral offset of the axle assemblies, axle-to-frame square or the vehicle’s wheelbase length.
The rear 3-link suspension adjustments control the axle/driveline pinion angle, axle-to-frame square and the axle
Illus. 145: These are the OE parts
that are eliminated or replaced with the installation of a Full-Traction Suspension 4” Ultimate package. The rear
track bar is not needed. The front track bar is replaced with the FTS unit. Six of these link arms were replaced
with FTS heavy-duty, adjustable types. New sway bar and stabilizer links, a new dropped pitman arm, new coil
springs and new shock absorbers round out this lift/suspension system. OE driveline and damper gave way to a rugged
CV-style rear driveshaft and new transfer case output yoke.
Note—You can find simpler “short-arm,” non-adjustable lift kits available for 2”-4” lifts on the
Jeep TJ Wrangler. However, Full-Traction Suspension’s 4” Ultimate package includes the rear 3-link conversion,
which also fits the FTS long-arm kits. (The front suspension is considered an adjustable short-arm type on the 4"
lift kit. A 6" lift kit requires long front arms.) Various manufacturers take different approaches to
suspension and goals. This FTS system aims at improved on- and off-highway performance and overcomes several
limitations of the OE suspension.
Illus. 146: Final check is the
disconnect link’s clearance at the new tires. This fitment will work well on-highway at normal wheel travel.
Off-pavement, under extreme suspension articulation, the links will be disconnected and out of the way. These are
stout disconnects. Always check for clearance here, as some tire widths and wheel rim widths can create
Illus. 147: Turn wheels to each
extreme with the axle moving over its range of travel. Check for tire-to-disconnect and brake hose clearance. After
driving the vehicle, verify that these clearances are still effective. Suspension settles slightly and road
dynamics can affect the movement and position of these components. Here, there is sufficient clearance at extreme
Illus. 148: This TJ Rubicon is now
setting 3” higher than stock. On a non-Rubicon model, the height increase is a full 4-inch chassis lift. The new
tires are Goodyear MTR 285/75R16 size on stock Rubicon wheel rims. Shallower backspacing in the 3.62”-3.75” range
will widen the track width and help offset the center-of-gravity changes created by a suspension lift. This system
is in place and ready for a trip to the wheel alignment shop.
Caution: Any chassis lift will raise the center-of-gravity. To restore your Jeep to its original
C.G., you must widen the track width. This can be done easily with the use of wheel rims that have shallower
backspacing than stock. Always restore C.G. to reduce risk of a vehicle
Illus. 149: The first stop is the
wheel alignment rack. At the local Goodyear tire store, a $40K alignment rack can quickly perform a four-wheel
alignment check. Here, we can determine the angles and alignment of the front and rear axle assemblies. The vehicle
will be checked for square and lateral offset of either axle assembly. Once the axle-to-frame square and wheelbase
is on specification, the common caster, camber and toe-in checks can be made.
TJ Wrangler wheel alignment and rear axle thrust specifications—courtesy of Jeep® Corporation.]
Illus. 150: First concern is
lateral offset of the axles, which also affects setback measurements. Axle offset is slight at -0.13-degrees. A
minor adjustment can correct both the offset and setback. This will also restore the wheelbase lengths
Illus. 151: The monitor screen
indicated the needed adjustments. The focus will be the rear axle lower link arms. We will reset the right rear
lower arm length slightly and note the results.
Illus. 152: Before making any
adjustments, a look at the caster angle, toe set and thrust angle suggests which adjustments are necessary. Front
caster at 5.3-degrees positive is acceptable, especially with a lift suspension and the front driveline/pinion
angle considerations. Toe is off slightly as expected with the altered slope on the steering tie-rods. Thrust angle
will be adjusted with the axle offset tuning.
Illus. 153: Shop owner is a
friend, and we discuss the necessary adjustments. Our conclusion is to adjust the lower right rear link arm length
and note the results. The adjustment will be slight. Removal of the forward frame bracket bolt allows quick access
to the adjustable head of the link arm.
Illus. 154: We turn this lower
(right rear) link arm head the slightest amount possible—a single rotation. After making certain the arm ends are
aligned properly, the jam nut is tightened securely.
Illus. 155: Link arm is aligned
with the bolt hole. The bolt reinserted and secured, we will look at the results of this
Illus. 156: This is an excellent
reading. The toe-in requires setting as expected. Thrust angle, however, is now right on the factory specification. Simply put, the
only adjustment required (outside of the common toe-set and steering wheel alignment) was the one-thread
lengthening of the right rear lower link arm! I managed to get this close with a simple protractor, string lines
and careful alignment of parts. These steps and the manufacturer’s instructions can get similar
Note—Front axle camber
reads slightly out of specification, due to distortion of the front axle housing. On a vehicle this new, such
distortion likely took place in the manufacturing process or possibly from vehicle tie-down during transport to the
dealership. It is so slight as to not create a problem. This measurement would probably meet new vehicle warranty
Illus. 157: Of the eight possible
adjustment points on this aftermarket suspension system, this one link arm was the only point adjusted. Lengthening
the arm one thread in this case restored the thrust angle and lateral offset measurements to meet specifications.
The axles are aligned properly and square. Wheelbase is correct for the suspension system and wheel travel. Frame
and axles are true. The Jeep will track properly with enough front axle caster angle to provide good “return to
center” feel after cornering. Rear driveline pinion angle is correct.
Illus. 158: We now look to the
toe-in set. This routine, common adjustment is part of any alignment procedure. Thrust angle, caster, lateral
offset and cross-checks of the chassis are all in order. I aligned truck front ends and frames with older
equipment, during the early electronic 4-wheel alignment era. This contemporary machine does everything short of
making actual adjustments! Beams shoot ahead, also accounting for cross-checks and lateral position of each axle.
User-friendly for a computer literate generation of techs, this equipment is capable of fine chassis tuning and
Illus. 159: While the machine
shows slightly less positive degree of caster than desired (OE
specification: 6-8 degrees positive) and slightly more negative
camber at the left side of the axle housing than specified (0.1-degree of excess negative camber), these current
settings will work well. If we set caster any more positive, the result will include a sharp front U-joint angle
with this chassis lift. The compromise still provides in excess of 5-degrees positive caster, providing the
necessary return-to-center feel on the highway, which lends itself to good cornering.
Note—There are several other readings that accompanied this alignment. Turning angle, steering
axis inclination, lateral offset, included angle and cross readings all met the factory specifications.
This Jeep will have normal tire wear, and settings are optimal for the Jeep TJ
Illus. 160: Simple toe-set is now
made. Long tie-rod has an adjustment sleeve that changes the length between the steering arms. This changes toe.
The adjustment made here is expected, as TJ linkage is a Y-type that changes toe-set when the distance between the
pitman arm and axle changes. Even with a dropped pitman arm, there is a need for minor toe-set changes. Toe-set is
the most common adjustment on front ends and considered routine.
Illus. 161: As the sleeve adjusts,
the screen must be watched closely. Impact of toe-set on other settings is negligible. Steering wheel alignment
will be necessary after setting the toe-in.
Illus. 162: This is the adjustment
point for aligning the steering wheel. The step is only performed after the toe-in is correct and all other
adjustments have been made. Never adjust the
steering wheel by repositioning the wheel from its OE location on the steering
shaft! By adjusting the steering wheel position as
shown, the wheel comes back to center. Here, the steering gear aligns with its high-point (center) in the
straight ahead driving position.
Illus. 163: While toe-set altered
the caster angle and thrust angle very slightly, each of these measurements are well within specification for this
Jeep TJ Wrangler. The critical measurements will each produce good handling on-highway and appropriate off-pavement
steering angles. This turned out to be a straightforward alignment procedure. Doing as much alignment work as
possible before heading for the frame and alignment
shop can save considerable time and produce the best
Illus. 164: Steering wheel on
center with the alignment set, this has been the complete four-wheel alignment needed. The head at the left front
wheel is similar to the heads at each of the four wheels. Precision equipment eliminates guesswork and
self-calibrates, providing continuous accuracy. The Jeep TJ Wrangler will handle precisely, benefitting fully from
the three-link rear suspension upgrade. The next and final stop is the muffler shop. A custom 'cat-back' system
will be fabricated to work with the new rear suspension.
165: The Jeep TJ's owner opted for a lower-restriction
performance muffler to accompany the new tailpipe. The muffler welds to original TJ Wrangler pipe flange. New rear
exhaust system will route to clear the FTS V-link suspension. Use of the factory (OE) catalytic converter and a
rear exit tailpipe help reduce noise.
Illus. 166: In
fabricating a cat-back system, the muffler shop places the new performance muffler in line with the Jeep TJ
Wrangler's original muffler position. Note sufficient clearance overall and OE (factory) insulation above the
muffler at the floorpan.
Illus. 167: Here
is the need for the new tailpipe section—the pipe must clear the V-link, brace, axle, fuel tank, cables, hoses,
shock absorber and body. A quality muffler shop can perform this work. Check with Full-Traction Suspension on the
availability of a "bolt-on" exhaust kit.
Illus. 168: Here
is one exit method for the tailpipe. The aim must always be to route exhaust fumes away from the tub and Jeep
occupants. When in doubt, route the pipe's exit at
the original equipment (OE) point.
Illus. 169: This
is a tailpipe routing option. Take clearance, trail abuse, vehicle occupant safety and noise into
account. Avoid using mid-vehicle "side exit"
pipes. They can make Jeep occupants ill, especially with a cloth top down and the vehicle
crawl pace off-pavement!
Driveline Needs and
Suspension lifts nearly always require rear driveline modifications on a Jeep YJ, TJ or JK
Wrangler. Lifts create more driveline slope, and the factory use of a slip-yoke driveshaft (on all but the Rubicon
models) typically causes a driveline angle problem. Yokes and U-joints can only operate to a given angle, and
slip-yokes will not operate on steeper angles. Drivelines operate
best and handle more torque with fewer degrees of U-joint angle.
While a slight (1.5-2
degrees) U-joint angle is necessary for proper roller bearing lubrication within the U-joint, too much angle
reduces U-joint life and the driveline stamina. In my
Jeep Owner’s Bible (Bentley Publisher, Cambridge, MA), I discuss at length the dynamics of U-joint angles and
driveline phasing. For the purpose of fitment and service work, three areas need attention:
1) minimizing the operating angles of
the U-joints and drivelines, 2) providing adequate spline engagement over the full range of axle travel or cycling,
and 3) matching the U-joint angles to prevent the shaft from self-destructing due to incompatible joint
Minimizing slope and
joint angles can be accomplished by use of a longer driveline or lowering the transmission/transfer case when
installing a suspension lift. There are special joint flanges available to increase the slope angle capability of a
driveline; however, when a shaft operates on a steeper angle, driveline stamina and torque capacity drop in
relationship to the slope increase of the driveshaft.
An innovative remedy is
found as OE equipment on the front drivelines of TJ and JK models: the use of a constant velocity (CV) or
double-Cardan type driveline. This same approach can benefit the rear driveline. By design, the CV double-joint
assembly is unique in that the two U-joint angles always cancel each other. The single Cardan U-joint at the
opposite end of the driveline is then set around 2-degrees, just enough to keep the U-joint's needle rollers moving
and lubricated. For the rear axle driveline upgrade, the 1.5-2 degree angle is met by rotating the axle housing's
pinion nose upward until it approaches a near-straight alignment with the new driveline’s tube
section. (Actually, this relationship should
be a 1.5 to 2.0-degree angle.)
The CV driveline is
stronger, minimizes angularity of the shaft and provides a solution for driveline angle issues on a shorter
wheelbase vehicle. Added benefits of the CV or double-Cardan system include far less vibration and a longer service
life. (When converting a YJ Wrangler to a non-disconnect front axle system, a CV driveline is necessary at the
front axle to reduce risk of driveline vibration.) While the front shaft is longer and operates at lesser joint
angles, wear reduction and smoother operation still make a CV style front driveline
Driveline angles are
critical. Actually, the slope angle, barring any binding problems due to excessive angularity, is only part of the
problem. Critical to driveline function and lifespan is the matching or cancelling of U-joint angles at each end of
the driveline. U-joint angles must cancel each
other. If they do not, a shaft will tear itself apart. By
design, a U-joint operating on an angle will speed up and slow down during each rotation. The opposing joint must
be in sync or phase with this speedup and slowdown. This is accomplished by placing each joint on an equal angle to
its opposing joint.
The U-joint crosses
must line up, too, or the driveshaft will be out-of-phase and quickly destroy
itself. On a slip-yoke driveline, phase alignment is
not an issue, as the tube and yoke flanges are fixed in position. When assembling a splined slip-coupler,
however, it is possible to misalign splines and place the U-joints out-of-phase.
Joint crosses must align with each
Lift kits and
powertrain upgrades can lead to driveline troubles. A Jeep's reliability, safety and the expense of broken parts
make the drivelines' design, fitment and stamina important.
Illus. 170: This is the difference
between a double-Cardan CV joint (lower) and the stock Rubicon single Cardan joint. The CV joint will reduce
driveline angle by providing two joints in a single assembly. These joints are hefty 1330 size and cancel each
other’s angle. This reduces vibration, stress and the actual tilt angle of each
Illus. 171: Here, I check a rear driveline angle at static, curb
height of the axle. A two-degree angle is optimal for this double-Cardan CV rear driveline. This slight angle at
the rear (single Cardan) joint will enable the bearings to rotate in the U-joint bearing caps. A zero degree
position will cause the bearings to remain in one position and wear out prematurely.
Note: For this check, the vehicle can be either parked securely with its wheels on the ground and
normally loaded, or place the Jeep safely on jack stands, with two beneath each of the axle housings. Normal,
curb or static weight should bear down on the axles when checking U-joint angles. Make sure the Jeep is secure
before crawling underneath it!
When working on your Jeep TJ or LJ Unlimited Wrangler, refer to
the factory (OE) Jeep® Service Manual for the vehicle
model year. Torque specifications, frame specifications, the wheel alignment specifications, driveline
torque specifications and suspension details—including torque settings and actual frame measurements—are
available in the Jeep® official workshop manuals. I consider these manuals a "must" for any
4x4 shop or Jeep owner who is serious about performing professional level work. See your
Mopar™ or Jeep® dealer for access
to these manuals, available in paper-bound and CD format!
— Moses Ludel
[Tool illustration—courtesy of
[Front suspension/axle torque for 2005
Jeep TJ Wrangler—courtesy of Jeep®.]
[Steering linkage torque for 2005 Jeep TJ Wrangler—courtesy of Jeep®
[Rear suspension torque for 2005 Jeep TJ Wrangler—courtesy of
Copyright 2010 © Moses
Ludel...Enjoy this comprehensive, color-illustrated article and photography by Moses Ludel. The article is
available solely at the 4WD Mechanix
Magazine website and can be viewed here as often as you
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Magazine website: www.4WDmechanix.com. As copyrighted material, this article and the photography cannot be
copied or distributed in any other form.—Moses