A constant-velocity (CV) joint transfers rotating power at a consistent speed even as the drive angle changes. This lets a front drive wheel receive smooth power while steering and moving over bumps, without the speed fluctuations of a simple universal joint.
Animated: how a CV Joint actually works
🔧 How It Works, Step by Step
1
Balls ride in curved grooves
In a common ball-type CV joint, hardened balls sit in matching grooves between an inner and outer race.
2
The cage holds the balls aligned
A cage keeps the balls positioned on the plane that bisects the joint angle, which is the key to constant velocity.
3
Torque passes at any angle
As the joint bends, the balls transmit torque smoothly without the speed variation a u-joint would create.
4
Grease and a boot protect it
Packed grease and a sealed rubber boot keep the joint lubricated and free of dirt and water.
🧩 The Key Parts
Inner and outer races
Provide the grooved surfaces that the balls ride in.
Ball bearings
Transmit torque while allowing the joint to flex.
Cage
Keeps the balls aligned for constant-velocity operation.
Rubber boot
Seals in grease and keeps out contaminants.
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🩺 Signs of a Failing CV Joint
Clicking or knocking during turns
Clunk on acceleration or deceleration
Vibration at speed
Grease leaking from a torn boot
Humming or grinding from the joint
⚠️ Common Problems
Boot failure
A cracked or torn boot lets grease out and grit in, which grinds down the joint and leads to failure.
Wear from contamination
Dirt and moisture inside the joint wear the balls and races, causing clicking and eventual breakage.
Loss of lubrication
When grease escapes, metal-on-metal contact rapidly destroys the joint.
💰 Cost to Fix
$150-$450typical range to repair or replace, parts and labor
❓ FAQ
What is the difference between a CV joint and a u-joint?
A CV joint maintains constant output speed through wide angles, ideal for driven steering wheels, while a u-joint varies speed and suits straight driveshafts.
Can a CV joint be repaired?
A joint can be repacked and re-booted if caught before damage, but a worn joint is usually replaced as part of a complete axle.
How do I know which CV joint is failing?
Clicking on turns points to the outer joint, while clunking or vibration during acceleration usually indicates the inner joint.
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