Coil Springs: What They Do and Signs They've Failed

What Are Coil Springs?

Coil springs are the helical steel springs that support your vehicle's weight at each wheel. They're the "elastic" component of the suspension — they compress when the wheel hits a bump, absorbing energy, and rebound to maintain ride height when the bump is past.

Coil springs work in partnership with shock absorbers (or MacPherson struts):

• The spring absorbs the energy and supports weight
• The shock absorber controls the spring's movement, preventing continuous bouncing

Most modern NZ passenger cars have coil springs on all four corners.

Types of Springs in NZ Vehicles

This article focuses on coil springs, the most common type on passenger cars.

How Do Coil Springs Fail?

Breakage (Most Common)

Coil springs can crack and break — usually at the top or bottom coil, which is the point of highest stress concentration. Causes include:

• Rust and corrosion — NZ coastal environments and road salt accelerate this
• Metal fatigue from years of repeated compression cycles
• Impact damage from hitting a pothole or kerb at speed
• Age — springs on high-km Japanese imports may be 15–25 years old

A broken spring often produces a loud clunk or bang when it first breaks, and the car will visibly sag on that corner.

Sagging (Fatigue)

Springs gradually lose their free length over time as the steel fatigues. The result:

• The vehicle sits lower than designed — ride height drops
• Handling is compromised — suspension geometry (camber, caster) changes
• Ground clearance is reduced — particularly relevant on rural NZ roads
• Premature wear on shock absorbers (working in a compressed range they weren't designed for)

Sagged springs don't usually have dramatic symptoms — the car just feels lower and handles slightly worse than it should.

Signs of a Broken or Failed Coil Spring

• Car sitting noticeably lower on one corner — stand back and look at the car on level ground
• Loud clunk or bang heard when the spring first broke (usually over a pothole)
• Tyre rubbing on the inner wheel arch on the low corner
• Handling changes — car pulling to one side or feeling unstable
• Clunking from the suspension as the broken coil end moves around
• Visible broken section if you look at the spring through the wheel arch

WoF Failure

A broken coil spring is a definitive WoF failure. Inspectors check:

• Visible spring breakage
• Abnormal ride height (vehicle sitting significantly lower than designed)
• Tyre contact with body or chassis components caused by spring failure

A broken spring can also damage the tyre sidewall as the broken end contacts the tyre on full suspension compression — a safety and tyre replacement issue on top of the spring repair.

Should Springs Be Replaced in Pairs?

Yes. Springs are always replaced in axle pairs (both front springs together, or both rears together):

• Springs sag and fatigue together — replacing one creates a handling imbalance
• Ride height will differ between sides if you mix a new spring with an old sagged one
• The cost difference between one spring and two is minimal in labour terms

NZ Cost to Replace

Wheel alignment should be checked after spring replacement — ride height changes affect alignment geometry.

Tip: If the springs need replacing on a car with high mileage or old shock absorbers, consider replacing both at the same time. The labour overlap means the combined job costs less than doing them separately.

When to Book a Mechanic

• The car visibly sits lower on one corner
• You heard a loud bang from the suspension recently
• A tyre is rubbing against the wheel arch
• WoF inspection noted a spring fault
• Clunking from the front or rear suspension that isn't tied to a pothole

Further Reading

• Find a mechanic near you
• MacPherson struts: how coil springs integrate with the strut
• Shock absorbers: working alongside coil springs
• Sway bar: another suspension component worth knowing