4WD Mechanix© Magazine…issue #6, July 2010. For Fast navigation, use the aDobe reaDer® “bookMarks” Feature...there is a bookMark For each listeD ‘table oF contents’ iteM! 4WD Tech: ‘DIY’ Wheel Alignment! Copyright © 2010 by Moses Ludel…This material may be distributed solely by download from www.4WDmechanix.com. Please refer others to the website for a free download copy! Page 25 4WD Mechanix© Magazine…issue #6, July 2010. For Fast navigation, use the aDobe reaDer® “bookMarks” Feature...there is a bookMark For each listeD ‘table oF contents’ iteM! Wheel alignment is a basic vehicle maintenance need. Suspension modifications, normal chassis and steering linkage wear, off-pavement trail pounding and the use of oversized tires can each affect front wheel alignment. 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 vehicles has a hypoid, solid rear axle assembly. The less complicated beam front axle is not just strong and durable. It also has fewer maintenance Since most trail vehicles upgrade to expensive, requirements. Camber is set at the factory with the oversized traction tires, premature wear of tires is jig-welding of the beam. Caster is adjustable for the always a concern. Periodic tire rotation and proper slight sagging of aged springs or the settling of wheel alignment are basic safeguards to prevent spring or link arm bushings. For all Jeep vehicles, a abnormal tire wear. common alignment need is toe-set. Copyright © 2010 by Moses Ludel…This material may be distributed solely by download from www.4WDmechanix.com. Please refer others to the website for a free download copy! Page 26 4WD Mechanix© Magazine…issue #6, July 2010. For Fast navigation, use the aDobe reaDer® “bookMarks” Feature...there is a bookMark For each listeD ‘table oF contents’ iteM! Caution: Wheel alignment is never a substitute for alignment can handle any vehicle with a solid, replacing worn or damaged parts. A bent steering hypoid rear axle system. knuckle, tie-rod or axle beam is a candidate for replacement. Straightening trail-damaged steering linkage or a bent knuckle is not safe practice. Periodic Alignment Needs 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 models unless an aftermarket lift kit has adjustable rear wheel link arms or there is suspicion of a bent rear axle or frame damage. To push the vehicle forward in a straight line, rear Thrust alignment does take rear axle shift, worn axle thrust must be perpendicular to the centerline springs, bad bushings or a bent frame into account. of the frame. When thrust is correct, a front wheel A shop that performs either four-wheel or thrust alignment assures precise steering and a normal steering wheel position. Copyright © 2010 by Moses Ludel…This material may be distributed solely by download from www.4WDmechanix.com. Please refer others to the website for a free download copy! Page 27 4WD Mechanix© Magazine…issue #6, July 2010. For Fast navigation, use the aDobe reaDer® “bookMarks” Feature...there is a bookMark For each listeD ‘table oF contents’ iteM! On turns, the inside wheel has a tighter turning Note: If you have no reason to suspect knuckle or angle than the outside wheel. This is “Ackerman spindle damage, checking the SAI is of lesser steer,” the result of the steering knuckle’s kingpin importance. If your Jeep rear axle is square with inclination, caster angle and the steering axis the frame and not bent, there is not a call for inclination (‘SAI’). Each of these variables affect thrust alignment. In the months ahead, I will share steering and the vehicle’s behavior when turning. information on how to easily set up a lift kit and Caster is often adjustable. When SAI is incorrect, adjust link arms to assure proper thrust and axle however, the most common cause is a damaged alignment with the frame. steering knuckle or bent spindle. Toe-Set Toe-in 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 item. 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 call for zero-degrees of toe set. Copyright © 2010 by Moses Ludel…This material may be distributed solely by download from www.4WDmechanix.com. Please refer others to the website for a free download copy! Page 28 4WD Mechanix© Magazine…issue #6, July 2010. For Fast navigation, use the aDobe reaDer® “bookMarks” Feature...there is a bookMark For each listeD ‘table oF contents’ iteM! Due to the thrust loads of the vehicle moving type, bias-ply tires should follow factory alignment forward (especially with oversized tires!), and the specifications. That toe-in might be in the 1/16”- slight movement of steering joints under load, toe is 3/16” range, typically a 1/8” setting. actually set so that tires “toe-in” slightly. This toe-in If using modern radial tires, toe-in should be near is measurable at the forward side of the front tires. zero, something like 1/32” for stock tires. (Modern alignment is actually measured in tenths of a degree, not inches.) High-end alignment equipment can check toe-set with projectors and electronic beams. As you will see in this segment of “4WD Tech,” toe-in can also be checked with basic tools. Camber 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 The tires’ design dictates toe-in requirements. outward, from a vertical centerline. If the top of the Bias-ply tires have a tendency to thrust outward tire tilts outward, camber is “positive.” If the top of under load. The classic Willys or Jeep CJ with OEM the tire tilts inward, camber is “negative.” Copyright © 2010 by Moses Ludel…This material may be distributed solely by download from www.4WDmechanix.com. Please refer others to the website for a free download copy! Page 29 4WD Mechanix© Magazine…issue #6, July 2010. For Fast navigation, use the aDobe reaDer® “bookMarks” Feature...there is a bookMark For each listeD ‘table oF contents’ iteM! Alignment specifications read in positive or negative Jeep beam-type axles with leaf springs or link degrees of camber. 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 settings. *Note: Camber can be corrected with aftermarket ball-joints or eccentric ball-stud seats. There is, however, no OEM provision for adjusting camber. By contrast, each front wheel on an IFS suspension moves up or down independently. Short (upper) and long (lower) control arm “SLA” suspension compensates for body/frame lean on corners. As the vehicle corners, the body/frame rolls, Jeep Liberty “SLA” Front Wheel Suspension (Parts causing the outside wheels to compress the springs. illustration is courtesy of Chrysler/Jeep Corporation.) This moves the wheels upward into the fender Copyright © 2010 by Moses Ludel…This material may be distributed solely by download from www.4WDmechanix.com. Please refer others to the website for a free download copy! Page 30 4WD Mechanix© Magazine…issue #6, July 2010. For Fast navigation, use the aDobe reaDer® “bookMarks” Feature...there is a bookMark For each listeD ‘table oF contents’ iteM! wells. The unloading inside wheels drop as the body Solid, beam front axle Jeep vehicles have a rolls outward. A functioning sway bar helps simpler approach. As the frame/body rolls on turns, minimize this body/frame roll. the axle, wheels and tires stay parallel to the ground—unless we’re rock crawling with wheels in On SLA suspension like the Liberty, late Grand the air! The leaf springs or coil springs compress, as Cherokee or Commander, tire track width remains suspension allows for this roll. relatively constant during this process. The arc of wheel travel is precisely engineered for maximum As the outside wheel compresses the suspension, control and long tire life. 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. Caster 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 center of the upper and lower ball joints or kingpin/knuckle bearings (on a vintage Copyright © 2010 by Moses Ludel…This material may be distributed solely by download from www.4WDmechanix.com. Please refer others to the website for a free download copy! Page 31 4WD Mechanix© Magazine…issue #6, July 2010. For Fast navigation, use the aDobe reaDer® “bookMarks” Feature...there is a bookMark For each listeD ‘table oF contents’ iteM! Jeep). That is the kingpin centerline. The forward or well. If not, suspect a bent or defective spindle or rearward tilt of this centerline, measured in steering knuckle.