What are CV Joints?
The flexible joints that transfer power from the gearbox to the wheels while the suspension moves up and down.
Simplified animation — not to scale.
In plain English
Constant Velocity (CV) joints are specialised universal joints fitted at each end of the driveshaft (also called a half shaft or axle shaft) on front-wheel-drive, all-wheel-drive and many four-wheel-drive vehicles. Their job is to transfer engine torque from the gearbox or differential to the front wheels at a constant speed, regardless of the angle created by suspension travel and steering. Each driveshaft has an inner CV joint (near the gearbox) and an outer CV joint (near the wheel). The outer joint usually handles the greater steering angle.
"Think of a CV joint like a flexible drinking straw with a bendy section in the middle. You can twist one end while the other stays at an angle, and the twist still transfers smoothly through the bend. The bendy rubber sleeve keeps the inside clean. If that sleeve splits, sand and water get into the bend and it quickly wears out — then it starts clicking every time you twist it."
How it works
Inside a CV joint, grooves in the inner and outer housings hold steel balls that ride in cages. As the joint bends (when the wheel steers or the suspension moves), the balls roll in their grooves and maintain an even rotational speed. This prevents the judder and vibration you would get from a simple universal joint. The entire assembly is packed with grease and protected by a rubber boot. If the boot splits and the grease escapes, dirt and water get in and the joint wears rapidly, leading to the characteristic clicking noise.
Signs of trouble
- ⚠Clicking or knocking noise when turning at full lock (e.g. pulling out of a parking space)
- ⚠Vibration or shudder under acceleration, especially from a standstill
- ⚠Grease sprayed inside the wheel arch (a split CV boot)
- ⚠A loud clunk when engaging drive from neutral or park
- ⚠Worn or cracked CV boot visible during inspection
- ⚠Whining or humming noise that changes with vehicle speed
CV boot only: £70–£150 fitted; full driveshaft with joints: £140–£320 fitted (OE parts can push this to £500+)
Always get a written quote. Prices vary by car, region, and parts brand.