Section 3.4: Pre-Alignment Inspection and Setup

Pre-Alignment Inspection and Setup

Performing a wheel alignment on a vehicle with worn suspension components, incorrect ride height, or mismatched tires is a critical diagnostic error. A technician must conduct a comprehensive pre-alignment inspection and ensure proper vehicle setup before mounting sensors or attempting adjustments. Any worn component will allow the wheel angles to shift dynamically, rendering the alignment useless and potentially unsafe.

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Ride Height Inspection

Ride height is the distance from specified points on the vehicle frame or body to the ground or suspension components. It must be checked before measuring alignment angles.

• Why It Matters: All suspension geometry—camber, caster, and toe—is engineered around a specific ride height. If a spring has sagged or the vehicle is overloaded, the control arms sit at an incorrect angle. On most SLA (short-long arm) and MacPherson strut suspensions, a low ride height increases negative camber and alters toe.
• Measurement Procedure: Ride height must be measured on a flat, level surface (preferably the alignment rack). The technician measures the height at manufacturer-specified points (e.g., from the lower control arm pivot bolt to the ground, or the rocker panel to the ground) and compares it to specifications.
• Causes of Incorrect Ride Height: Weak or sagged coil springs, broken leaf springs, incorrect aftermarket lowering kits, or excessive vehicle cargo/weight. If ride height is out of specification, the springs must be replaced or the suspension adjusted (e.g., torsion bars) before an alignment can proceed.

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Tire Pressure, Size, and Condition

Tires are the interface between the suspension and the road. They must be inspected and prepared:

• Tire Pressure: Check and adjust the inflation pressure of all four tires to the specifications listed on the vehicle's tire information placard (located on the driver's door jamb), not the maximum pressure listed on the tire sidewall. Unequal tire pressure changes the rolling radius of the tires, causing a pull, and alters the vehicle's level, which affects camber and caster readings.
• Tire Size and Wear: Tires on the same axle must be the same size, construction type (radial/bias-ply), and have similar tread wear. A tire with significant wear will have a smaller outer diameter than a new tire. Mismatched tire diameters cause the vehicle to pull to the side with the smaller tire.
• Radial Ply Runout (Tire Pull): Internal belt separation or manufacturing defects can cause "radial pull." This can be diagnosed by swapping the front tires from side to side. If the direction of the steering pull reverses, the issue is a tire pull, not an alignment problem.

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Suspension and Steering Wear Inspections

Every joint, bushing, and link in the steering and suspension systems must be checked for excessive play.

1. Wheel Bearing Play

A loose wheel bearing allows the wheel and tire assembly to wobble. This play directly distorts the wheel alignment sensor readings.

• Checking Procedure: Raise the vehicle so the tire is off the ground. Grasp the tire at the 12 o'clock and 6 o'clock positions and wiggle it back and forth. If play is felt, verify whether it is in the wheel bearing or the ball joints. Worn bearings must be replaced or adjusted to specification before proceeding.

2. Steering Linkage (The Dry Park Test)

The best way to inspect steering components for play is under load.

• Dry Park Test: With the vehicle on a drive-on lift or on the ground, have an assistant rock the steering wheel back and forth rapidly (about 45 degrees in each direction). Underneath the vehicle, the technician physically feels and inspects the tie rod ends, center link, idler arm, pitman arm, and steering rack mounts. Any visible movement or play in these joints (especially axial play in tie rod ends) is grounds for replacement.

3. Suspension Component Checks

• Ball Joints: Lower and upper ball joints must be inspected using the manufacturer's recommended procedure. For load-carrying ball joints, the suspension must be supported to unload the joint before checking for play with a dial indicator or pry bar. Non-load-carrying joints (follower joints) are checked with the suspension loaded or unloaded depending on the design.
• Control Arm Bushings: Inspect rubber bushings for cracking, tearing, dry rot, or centering. Use a pry bar to check for excessive movement of the control arm shaft within the bushing.

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Wheel Runout and Alignment Rack Setup

Even a brand-new wheel rim is not perfectly round. Wheel runout is the amount of wobble or deviation from a perfect circle.

• Lateral Runout: Side-to-side wobble of the rim.
• Radial Runout: Up-and-down hop of the rim.

To prevent runout from affecting alignment measurements, technicians must perform a runout compensation procedure on the alignment rack:

1. Mount the Sensors: Mount the alignment targets securely to the outer lips of the wheel rims.
2. Rolling Compensation: With the alignment rack turnplates and slip plates locked, the technician rolls the vehicle backward, then forward, a short distance. The alignment computer tracks the targets' movement. By analyzing the rotational path, the computer calculates the lateral runout of each wheel and mathematically subtracts it from the final alignment readings.
3. Unlock Plates: Once compensation is complete, the turnplates under the front wheels and the slip plates under the rear wheels must be unlocked (by removing the lock pins). This allows the wheels to move freely as adjustments are made, preventing suspension binding that would cause incorrect readings.