What does a CV Joint do?


CV Joints or Constant Velocity Joints allow a rotating shaft to transmit power through a variable angle, at constant rotational speed, without an appreciable increase in friction or play. They are mainly used in front wheel drive and all wheel drive cars. However, rear wheel drive cars with independent rear suspensions typically use CV joints at the ends of the rear axle half shafts.


These joints are very strong, and are usually highly over specified for a given application. Maintenance is usually limited to checking that the rubber gaiter (dust/weather boot) that covers them is secure and not split. If the gaiter is damaged, the grease that the joint is packed with will be thrown out. The joint will then pick up dirt, water, and road deicing salt and cause the joint to overheat and wear, and the grease can also contaminate the brakes. In worst case, the CV joint may disjoin causing the vehicle to stop moving or lock up rendering the car incapable of steering.


CV Joint Diagnosis

Constant velocity joints are usually reliable and largely trouble-free. The two main failures are wear and partial seizure.


Wear in the outer joint usually shows up as vibration at certain speeds, a bit like the vibration caused by an unbalanced wheel. To determine if the joint is worn, a driver should find a big empty parking lot and drive the car slowly in tight circles, left and right. Worn joints will make a rhythmic clicking or cracking noise. Wear in the inner joints shows up as a “clunk” or “pop” when applying power, or if severe, when lifting off the throttle.


Partial seizure causes a strange “pattering” sensation through the suspension. It is caused by the joint overheating, which in turn is usually caused by the outer joint gaiter having split, allowing the joint to throw out its grease. If caught in time, one can clean the joint carefully, repack with grease and replace the gaiter. Kits which include the grease, gaiter and retaining clips are available from most automotive manufacturers. Some universal gaiters are split lengthwise enabling them to be fitted without having to disassemble the wheel hub and CV joint.