This article is part of a 6-part series, Part 5. It covers the specific hardware used to make front-end alignment changes and how rear wheel alignment is performed on modern vehicles. Knowing how these adjusters work is what lets a technician turn a specification on a screen into a real mechanical correction.
Lever-Action and Pivot Displacement
Front-end alignment adjustments rely on shifting the spatial coordinates of suspension pivot points relative to the vehicle frame. By altering the length or mounting position of specific control members, the steering knuckle is forced to tilt for camber or rotate for caster.
Eccentric displacement involves utilizing an offset bolt or cam washer to convert rotational motion into linear displacement of a suspension arm. Strut rod tension and compression means adjusting the effective length of a longitudinal support member, called a strut rod, to pull or push the lower control arm, thereby changing the fore-aft angle of the steering axis. Tower relocation means shifting the upper mounting point of a MacPherson strut within the vehicle body to alter the inward or outward orientation for camber, or the forward or backward orientation for caster, of the entire strut assembly.
Pivot and Linkage Interaction
Suspension components function as a series of interconnected levers where moving one point of a triangle changes the remaining angles.
The lower control arm relationship to caster and camber is that on dual-eccentric systems, rotating the front or rear eccentric bolt independently or in unison allows for simultaneous or independent changes to caster and camber. The strut tower relationship to axis inclination is that moving the upper strut mount changes the Steering Axis Inclination (SAI) alongside camber. Threaded linkage means threaded sections on strut rods or tie rods provide infinite adjustability within a fixed range, constrained by the number of remaining threads and the physical limits of the bushings.
Adjustment Mechanism Design Constraints
Mechanical interfaces are designed to lock geometry under high dynamic loads while allowing for precision tuning during service.
Strut rod adjustment is accomplished by moving adjusting nuts on a threaded rod that connects the lower control arm to the vehicle frame. Eccentric cam bolts are used at the upper or lower control arm pivot points or at the base of a MacPherson strut. Rotating the bolt head moves the arm or knuckle inward or outward. Slotted mountings work as follows. Strut towers have slotted holes at the top of the tower that allow the strut assembly to slide. Control arm mounts have slotted holes in the vehicle frame or control arm that allow for lateral or longitudinal shifting of the pivot bolt. Shim placement means that on specific rear-wheel-drive architectures, shims are inserted or removed from both sides of the upper control arm pivot shaft to move the arm in relation to the frame.
Local Shop Note:
This brings back a story I picked up from a technician out on West Lee Road in Albion, N.Y. He was at an AVI OnDemand seminar, and he was telling me about an SUV that came in with a complaint that the front tires were wearing on the inside edge, and the vehicle would pull to the right under hard braking. The customer had already paid for two alignments at other shops. Still pulled and wore tires.
He put it on the alignment rack and checked all the angles — caster and camber were within spec, and toe was set correctly. But when he looked at the caster split, he found the left front was at +3.8 degrees and the right front was at +2.9 degrees. That 0.9-degree split was causing the pull under braking — the vehicle was drifting toward the side with less positive caster.
He started checking the adjustment hardware. The right front control arm had an eccentric cam bolt for caster adjustment. When he loosened the bolt to rotate the eccentric, he found the cam was seized in the bushing sleeve. The previous shop had just set toe and called it done, ignoring the seized eccentric. He freed the eccentric, set the caster to match the left side, and re-checked all angles. The vehicle tracked straight after that, and the tire wear stopped.
If there’s one thing to remember from that story, it’s that adjustment hardware has to be free to move if you’re going to use it. A seized eccentric cam or frozen adjuster will lock the angle in place, and you’ll never get the alignment right. Always check that your adjusters are free before you start making changes. And never assume an alignment is good just because the toe is set — caster and camber splits matter, especially under braking.
Locking Sequence and Bushing Bind Prevention
The engineering rationale for these interfaces is to maintain a fixed-point reference while allowing for manufacturing tolerances and road-wear compensation.
The locking sequence means that once an angle is established, locknuts and pivot bolts must be torqued to specifications to ensure the eccentric or threaded rod does not migrate under suspension travel. Friction and bind considerations mean adjustments must be performed with the suspension at curb height or on a friction-reducing turnplate to prevent bushing bind, which would otherwise result in a false reading. Symmetry of adjustment means that on systems with dual eccentrics or shims, adjustments must be balanced to ensure that a change intended for camber does not inadvertently pull the caster out of specification.
Rear Wheel Alignment and Advanced Adjustment Methodology
Total Vehicle Tracking and Compliance
Rear wheel alignment is the mechanical calibration of the non-steering axle to ensure it remains parallel to the vehicle centerline and perpendicular to the direction of travel.
Total alignment means modern lightweight suspension systems require four-wheel alignment because rear-axle deviation creates a thrust angle that forces the front wheels to steer off-center to maintain a straight path. Compliance compensation means static alignment settings for rear wheels are engineered to counteract the mechanical deflection, which includes bushing and linkage flex, that occurs under engine torque and road resistance.
Lateral and Longitudinal Stability
The rear suspension geometry dictates the squareness of the chassis, which directly impacts front-end steering effort.
Rear toe versus steering center means that incorrect rear toe settings shift the thrust line. If the rear wheels point to the left, the driver must turn the steering wheel to the right to prevent the vehicle from drifting, even if front alignment is perfect. Four-wheel steering dynamics means that in vehicles equipped with active four-wheel steering, the rear wheels utilize a dedicated steering gearbox or actuators. Failure in this system locks the rear wheels in a non-neutral position, necessitating specialized electronic resets and mechanical locking tools during alignment.
Rear Toe Tolerances and Indexing Requirements
Rear toe settings are similar to the front. Rear toe is adjusted by lengthening or shortening a toe link or rotating an eccentric bolt. Non-adjustable axles means that on many front-wheel-drive vehicles with solid rear axles, the alignment is fixed. Deviation from factory specifications indicates structural damage or failed trailing arm bushings. Indexing means when removing struts or control arms for adjustment, index marks must be used to ensure the component returns to the precise coordinate required to maintain the established angle.
Rear Adjustment Hardware Specifications
Manufacturers employ several specific mechanical interfaces to allow for post-assembly fine-tuning of suspension geometry.
Alignment shims are thin metal or plastic spacers inserted between the upper control arm pivot shaft and the vehicle frame. Removing or adding shims moves the control arm inward or outward to reset camber and caster. Slotted mountings are the use of elongated bolt holes in the control arm or frame. Adjusting the position of the bolt within the slot provides lateral movement for camber or caster calibration. Eccentric cam bushings are pivot bushings containing an offset center sleeve. Rotating the bushing within the control arm housing effectively changes the arm’s length or pivot point. Threaded rod adjusters, also called toe links, are utilized primarily for rear toe. Rotating the threaded sleeve moves the rear wheel in or out relative to the chassis centerline.
Component Removal and Final Torque Conditions
Component removal for adjustment means that in some MacPherson strut designs, the entire strut assembly must be lowered or removed to clear mounting holes or file slots for camber or caster kits. Friction reduction means alignment must be verified with the vehicle’s weight on the suspension at curb height. Turnplates or slip plates are required under the tires to prevent tire scrub from creating false tension in the suspension links during adjustment. Final torque means all adjustment locknuts and pivot bolts must be torqued only after the vehicle is at its final ride height to prevent bushing wind-up, which would cause premature bushing failure and alignment migration.
The key takeaway is that front adjustments use eccentrics, slots, and shims, while rear alignment requires its own hardware to set thrust angle correctly. Proceed to Part 6.