Part 3: Suspension & Wheel Alignment, Driveline Upgrades and Exhaust

[Illustration courtesy of Jeep® Corporation.]

   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 assemblies.

     With 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 housing position.

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 interference.

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 left turn.

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 roll-over.

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.

[2005 Jeep 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 side-to-side.

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 adjustment.

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 results.

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 requirements.

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 precise results.

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 Wrangler.

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 results.

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.

Illus. 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 at a crawl pace off-pavement!

Driveline Needs and Upgrades

     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 angles. (See the   Jeep Owner’s Bible for further details.)

  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 desirable.

  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 other.

  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 U-joint.

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 Jeep® Corporation.]

[Front suspension/axle torque for 2005 Jeep TJ Wrangler—courtesy of Jeep®.]

[Steering linkage torque for 2005 Jeep TJ Wrangler—courtesy of Jeep® Corporation.]

[Rear suspension torque for 2005 Jeep TJ Wrangler—courtesy of Jeep® Corporation.] 

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 like. If you wish to share the article with friends or professional colleagues, please refer them to 4WD Mechanix Magazine website: www.4WDmechanix.com. As copyrighted material, this article and the photography cannot be copied or distributed in any other form.—Moses Ludel