What Is a CV Joint?
CV stands for Constant Velocity — and that describes exactly what these joints do. They transmit drive power from the transmission to the wheels at a constant rotational speed, even as the suspension moves up and down and the steering turns the wheels.
Without CV joints, the driveshaft couldn't handle the changing angles required by suspension travel and steering. The joints use a set of precision ball bearings inside a grooved race, all packed in grease and sealed inside a rubber CV boot.
Where Are They on the Car?
On a front-wheel drive vehicle (like a Toyota Corolla, Mazda Demio, or Honda Jazz), each front wheel has a CV axle shaft with:
- An outer CV joint — at the wheel hub end, handles steering angles
- An inner CV joint — at the gearbox end, handles suspension travel
On all-wheel drive and 4WD vehicles (Subaru Impreza, Toyota Hilux), CV joints appear on all four corners.
The CV Boot: The First Line of Defence
The CV boot is the black rubber accordion-style sleeve you can see behind each front wheel. It seals the joint and holds in the grease that lubricates the ball bearings.
When a boot cracks, splits, or is torn by road debris:
- Grease is flung out onto surrounding components
- Dirt, water, and grit enter the joint
- The joint wears rapidly — often failing within weeks to months of boot damage
A split CV boot costs $150–$300 to replace. A failed CV joint costs $400–$800+. Catching a torn boot early saves significant money.
Signs of a Failing CV Joint
Clicking on Turns
This is the classic outer CV joint failure symptom. A clicking, popping, or clunking noise when turning — especially sharp, slow turns like in a car park or reversing — indicates the outer joint is worn.
- The noise gets louder as the joint wears further
- Often heard pulling out of driveways or in roundabouts
- More pronounced under load (accelerating through a turn)
Vibration or Shuddering
A vibration or shuddering when accelerating in a straight line often points to a worn inner CV joint or a bent axle shaft.
Clunking When Changing Direction
A clunk or thud when moving from reverse to drive, or when pulling away, can indicate a worn inner joint or loose joint components.
Grease on the Inside of the Wheel Rim
Flung grease from a split boot coats the inside of the wheel rim — a visible sign to check for on any vehicle inspection.
What Happens If You Ignore It?
A failing CV joint that's left to deteriorate will eventually disintegrate. In severe cases:
- The axle shaft can separate entirely while driving
- Loss of drive to one wheel
- In extreme cases, the axle can contact the road, causing loss of control
- A completely failed joint requires more extensive disassembly
Don't ignore CV clicking — it progresses predictably and the cost of repairs increases significantly the longer it's left.
WoF Failure Risk
Split or missing CV boots and worn CV joints are common WoF failure points in NZ. Inspectors specifically check:
- Condition of CV boots (tears, splits, missing)
- Joint play and condition
- Grease leakage
A torn boot that hasn't yet led to joint failure will get a WoF advisory or failure notice, prompting repair before the next inspection.
NZ Cost to Fix
| Job | Typical NZ Price |
|---|---|
| CV boot replacement (outer, one side) | $150–$300 |
| CV boot replacement (inner, one side) | $200–$350 |
| Outer CV joint replacement | $350–$650 |
| Full CV axle shaft replacement (often cheaper than joint alone) | $400–$800 |
| Both sides (symmetrical wear is common) | $700–$1,400 |
Note: On many vehicles, replacing the entire CV axle shaft (joint, boot, and shaft as an assembly) is actually cheaper than replacing just the joint, because remanufactured shafts are widely available and use less labour than dismantling an old joint.
When to Book a Mechanic
- You hear clicking or clunking when turning in a car park or on a roundabout
- You notice grease on the inside face of a front wheel
- A WoF inspection noted a torn CV boot
- You're buying a used vehicle — a CV joint check is standard in a pre-purchase inspection