What Are MacPherson Struts and How Are They Different from Shock Absorbers?

What Is a MacPherson Strut?

The MacPherson strut is the most common type of front suspension found on modern NZ passenger cars. It's an integrated assembly that combines several functions in one unit:

• The shock absorber (damper) — the hydraulic cylinder that controls spring movement
• The coil spring perch — the strut body provides the mounting point for the coil spring
• The steering knuckle — the lower part of the strut directly holds the wheel hub and connects to the tie rod end for steering
• The upper strut mount — a rubber-and-bearing mount at the top that allows the strut to rotate when steering

You'll find MacPherson struts on the front of virtually every small and medium NZ car: Toyota Corolla, Mazda 3, Honda Jazz, Suzuki Swift, Mazda Demio, and many more.

How Is It Different from a Standard Shock Absorber?

On a conventional suspension setup (used on rear-wheel drive cars, 4WDs, and many rear axles):

• The spring and shock absorber are separate components
• The shock absorber can be replaced without disturbing the spring
• Replacing just the shock is simpler and cheaper

On MacPherson strut suspension:

• The spring sits around the strut (shock absorber body)
• Replacing the shock requires disassembling the strut — compressing the coil spring with a special tool, removing the top mount, separating the spring
• The shock absorber insert (cartridge) or the whole strut assembly can be replaced
• The spring, bearing, and top mount are often replaced at the same time

This makes strut work more involved (and more expensive) than a simple shock replacement.

Parts of a MacPherson Strut Assembly

Any of these can wear independently. Sometimes only the shock is worn; other times the spring or top mount has also failed.

Signs of MacPherson Strut Problems

Bouncing or Poor Damping

Same symptoms as worn shock absorbers — the car bounces after bumps, wallows in corners, and nose-dives when braking.

Knocking or Clunking From the Front Suspension

Often the upper strut mount bearing — a common failure. You'll hear a knock when going over small bumps or when the wheel reaches the end of its steering travel. Can also be a worn bump stop.

Steering Feels Rough or Gritty

The strut rotates on its bearing when you turn the steering wheel. A worn or seized bearing makes the steering feel notchy, stiff at low speed, or rough through the wheel.

Leaking Oil From the Strut

Oil seeping from the shock body indicates a failed damper seal — the shock is no longer damping correctly.

Sagging Corner

If one coil spring has broken, the car visibly sits lower on one corner — often very obvious when parked on flat ground. See coil springs.

Steering Pulling After Tyre Work

The strut geometry affects camber angle. A bent strut can cause persistent steering pull that doesn't resolve with alignment.

WoF Relevance

Strut condition is inspected at every WoF:

• Leaking dampers — fail
• Broken or collapsed springs — fail
• Seized strut top bearing affecting steering — fail
• Excessive suspension movement from worn dampers — noted

NZ Cost to Replace

Wheel alignment is required after strut work — the geometry changes any time the strut assembly is disturbed.

Tip: When replacing a strut, it's usually worth replacing the coil spring (if it has high mileage or any cracking), the top mount, and the bump stop at the same time. These parts are cheap and the labour is already included.

When to Book a Mechanic

• Knocking or clunking from the front on small bumps or speed humps
• Steering feels notchy or rough through the wheel
• Car bounces excessively or wallows in corners
• Visible oil on the strut body
• One corner of the car sitting visibly lower

Further Reading

• Find a mechanic near you
• Shock absorbers: what they do and how to test them
• Coil springs: what they do and signs they've broken
• Wheel alignment: why it's needed after suspension work