7.3 Dampers, Ball Joints, Bushes, Sway Bars & Suspension Operation

Create the load condition that reveals the defect

Suspension movement changes when the vehicle is on its wheels, lifted by the body, or supported under an arm. Use NZTA Technical Bulletin 4 and manufacturer information to choose a jacking point and test method. An incorrect load state can hide a worn joint or make a healthy joint appear loose.

Shock absorbers and struts

Inspect security, body/rod damage, bushings, attachments, and evidence of damping-fluid loss. Page 9-1 rejects excessive leakage, not every trace of oil. NZTA Technical Bulletin 9 distinguishes light misting—a thin film that can result from normal seal lubrication—from leakage that forms runs, drips, or shows significant loss. Cleanliness, pattern, and recurrence matter.

Assess damping where the approved method allows. Repeated uncontrolled oscillation, binding, or a detached unit supports a failure, but a simplistic “one bounce only” rule is not a universal VIRM measurement.

For a MacPherson strut or similar assembly, check the upper support bearing. Excessive play, roughness, or stiffness is specifically rejected. Observe spring wind-up, knocking, or erratic rotation while steering safely.

Ball joints, kingpins, and bushes

Load or unload each joint as its design requires, then apply controlled force. Compare movement with manufacturer specifications. Reject insecurity, damage, excessive wear/play, or binding. Do not puncture boots or use destructive force.

A split protective boot is assessed under the applicable component wording and consequences; page 9-1 specifically lists a split steering rack boot, while other joint boots require the correct current clause. The presence of grease alone is not a substitute for assessing the joint.

Bushes should retain the component and allow designed movement without metal-to-metal displacement, separation, or excessive play. Rubber surface checking can be cosmetic; tearing, missing material, separation from sleeves, or movement affecting control may fail. Inspect control arms for cracks, deformation, corrosion, and poor repairs.

Sway bars, links, and operation

Sway bars, links, brackets, and bushes must be secure and serviceable. Missing or disconnected components are evaluated against the vehicle design and modification provisions. Check clearance through steering and suspension movement: tyres, arms, springs, brake hoses, drive shafts, and body structure must not interfere dangerously.

Observe ride-height controls and air systems reaching and retaining normal state. A warning or leak connected to a safety-critical suspension/steering fault requires the appropriate VIRM result.

Mounting structure

For every joint or damper fault, inspect the supporting structure. Insecurity, or corrosion damage, buckling, or fractures within 150 mm of a steering/suspension mounting, is a separate reason. A new ball joint bolted to a cracked arm or corroded mount does not restore safe control.

Practical sequence

1. Identify suspension type and correct support points.
2. Inspect at normal ride height for stance, bellows, leaks, and interference.
3. Support/load as required and test each joint and bearing.
4. Inspect bushes, arms, sway bars, links, dampers, and upper mounts.
5. Turn steering and cycle safe movement to reveal binding or contact.
6. Compare movement to manufacturer data and apply the misting bulletin.
7. Record component, position, test condition, and observed evidence.

Scenario

A damper has a light, uniform oily film near the rod seal but no run or drip and still operates normally. That may be misting, not excessive leakage. A wet trail running down the body with loss of damping supports rejection. The decision is evidence-based, not “any oil fails.”

Repeatable joint testing

Before applying leverage, identify whether the joint is load-carrying and where the spring force acts. Support the arm or body so the ball is unloaded when the specified method requires; otherwise spring preload can hide movement. Use controlled force near the joint, not a long bar that bends healthy components or damages boots.

Compare left and right only as a clue, not as a standard—both sides can be worn. Manufacturer limits override symmetry. After finding movement, observe the stud, housing, bush sleeve and mounting separately so the record names the actual source. On a recheck, reproduce the same support and force; a different method can create an apparent improvement or disagreement.

Final suspension checkpoint

Lower the vehicle safely and verify that components settle into normal position, hoses and wiring retain clearance, and any air system returns to standard ride height without a safety warning. Recheck fast visual indicators from both sides. If the road test is part of the approved process, use it to corroborate noise, binding or directional effects—not to override a visible cracked, insecure or excessively worn component.