Shock Absorbers (Dampers): What They Do and When to Replace Them

What Is a Shock Absorber?

A shock absorber (also called a damper) is a hydraulic device that controls the movement of your car's suspension. It works in partnership with the suspension springs — which support the vehicle's weight — to absorb the energy from road bumps and prevent the car from continuing to bounce.

Without shock absorbers, your car would bounce up and down repeatedly after every bump, making it nearly undriveable.

Shock Absorbers vs. Springs: What's the Difference?

These two components are often confused:

• Springs (coil springs, leaf springs) support the vehicle's weight and absorb the initial bump energy
• Shock absorbers dampen (control) the spring's movement — preventing it from continuing to oscillate

Think of jumping on a trampoline: the trampoline springs absorb the impact, but without friction they'd keep bouncing. Shock absorbers provide that friction to bring motion under control quickly.

See also coil springs for more on spring failure.

How Do Shock Absorbers Work?

A conventional shock absorber is a cylinder containing a piston and hydraulic fluid (oil). As the suspension moves:

• The piston moves through the fluid
• Small holes (valves) in the piston restrict fluid flow, creating resistance
• This resistance absorbs energy and slows the spring's movement
• Some shocks also have gas (nitrogen) chambers to improve performance and prevent foaming

Types of Shock Absorbers on NZ Vehicles

• Twin-tube shocks: Common, economical; found on most passenger cars
• Monotube shocks: Higher performance, better heat dissipation; found on some SUVs and sports cars
• MacPherson struts: The shock absorber is integrated into the strut assembly — see MacPherson struts

Signs Shock Absorbers Are Worn

Excessive Bouncing

After a bump or dip, the car continues to bounce rather than settling quickly. Do the "bounce test": push down firmly on one corner of the car and release — it should rise once and settle, not continue oscillating.

Body Roll in Corners

Worn shocks allow excessive body lean when cornering — the car feels like it's wallowing or rolling more than it should.

Nose-Diving When Braking

The front of the car dips significantly under braking (a sign of worn front shocks). This also increases braking distances because less weight stays on the rear wheels.

Aquaplaning More Easily

Worn shocks mean the tyres don't maintain as consistent contact with the road surface. This is particularly dangerous on wet NZ roads — the vehicle aquaplanes at lower speeds and feels unsettled in wet conditions.

Uneven Tyre Wear

Shocks that allow the wheel to bounce allow tyre "hopping" at speed, causing a cupped or scalloped wear pattern across the tread.

Leaking Oil

A shock absorber with oil seeping from the body has a failed seal. This is a tell-tale sign of a shock that needs replacement. Some light surface staining is normal; active weeping is not.

WoF Relevance

Shock absorber condition is checked at every WoF inspection:

• Inspectors perform the bounce test and check for oil leaks
• Excessive body movement on the test drive is noted
• Active oil leaks from shocks are typically a WoF failure or advisory
• Badly worn shocks affecting handling safety will fail

How Long Do Shocks Last?

Most manufacturers suggest inspecting shocks at around 80,000 km and expecting replacement by 100,000–150,000 km. NZ driving conditions — rural roads, broken urban surfaces, speed bumps — can shorten this life considerably.

Japanese imports frequently arrive with original shocks at 100,000+ km.

Replace in Pairs

Shocks should always be replaced in pairs (both fronts together, or both rears together). Replacing only one creates an imbalance in handling — the new side has noticeably better damping than the old side.

NZ Cost to Replace

When to Book a Mechanic

• The car bounces more than once after a bump
• Excessive body roll when cornering
• Oil visible weeping from a shock body
• Uneven or scalloped tyre wear (one possible cause)
• WoF noted worn shock absorbers

Further Reading

• Find a mechanic near you
• MacPherson struts: how they differ from shocks
• Coil springs: what they do and signs of failure
• Wheel alignment: how worn suspension affects alignment