CV (Constant Velocity) joints are clever bits of engineering used on all front-wheel drive cars, and many real-wheel and 4-wheel drive vehicles too. CV joints transfer torque from the transmission to the drive wheels at a constant speed, while accommodating the up-and-down motion of the suspension, and the turning of the wheels whiles cornering.
Inner CV joints connect the drive shafts to the transmission, while the outer CV joints connect the drive shafts to the wheels. The joints rely on special grease to keep them lubricated, and this is kept in place by rubber “CV boots”, which don’t look a lot like boots, more like black corrugated sink plungers. These keep the grease in, and dirt out, of the CV joints.
CV Joint Problems
CV joints don’t need any maintenance and can last the life of the vehicle as long as the protective CV joint boots remain undamaged.
The most common problem with the CV joints is when the protective boot cracks or gets damaged, letting the grease out and moisture and dirt in. This inevitably causes the CV joint to wear very quickly, and eventually of course it will fail due to lack of lubrication and corrosion. The outer CV joint boots are more liable to break as they have to endure more movement than the inner ones.
CV boots problems are one of the most common causes of MOT failures – a small split can cause the grease, because of the closeness to the brakes, to contaminate the brake pads and discs.
Signs of a Damaged CV Joints and Boots
A crack or tear in the rubber, often with grease oozing out, is the most common indication that the CV boot is failing. If the crack is bigger or long-standing, you may also see dark grease splattered on the inside of the wheel rim.
Once the CV joint itself starts to wear, the first symptom is a clicking or popping noise when cornering. If you continue to drive with a damaged CV joint boot, the CV joint will wear out and eventually fail, and can even disintegrate while driving and make the car undriveable.
Inner CV joints failures are less common, but one of the symptoms of a failed inner CV joint is shudder or side-to-side shaking during acceleration. Once again, complete failure of this joint will prevent power being transmitted from the engine to the wheels, so the car won’t be going anywhere until the joint is repaired.
CV Joint Repairs
If a damaged CV joint boot is spotted before the joint itself is damaged, then fresh grease can be applied and a new boot fitted – a relatively inexpensive repair, although quite a bit of labour is involved to remove and refit the boot.
If the CV joint itself is worn out it will have to be replaced with a new or reconditioned part. Sometimes the CV joint is an integral part of the driveshaft, which means the whole driveshaft will need to be replaced.