Constant-velocity (CV) joints are used to connect two rotating shafts that meet at an angle, and they allow for power and torque to be transmitted from the engine to the wheel without causing too much commotion. They are most commonly found on front-wheel drive and all-wheel drive vehicles, and help power transfer more fluidly across wide angles. Most FWD and AWD vehicles have four CV joints associated with the front axle, two inner joints and two outer.
There are a variety of styles that CV joints come in, such as the Rzeppa joint, which was named after its creator Alfred Rzeppa. This CV joint consists of a spherical shape with six grooves dividing the inner sphere like orange slices. A ball bearing fits in each groove, and a cage is fitted around this sphere to keep the balls in place and guide them along the groove. This allows for movements to accompany large angle changes when the wheels turn, which is why these are often found on the outside of front axles. Double cardan joints are often used in a steering column setup and sometimes takes the place of Rzeppa joints in AWD vehicles used on rugged terrain. There are also tracta, weiss and tripod joints.
On average, most CV joints should last approximately 100,000 miles. However, this can vary between makes and models, and your vehicle's owner's manual will provide a more accurate estimate of the joint's lifespan. CV joints do not commonly break down, since they have protective rubber boots that prevent unnecessary wear. Those placed on the outer side of the axle are more likely to break down faster than inner CV joints
However, the boot material is more susceptible to breaking down, and if it is torn, particles of dirt and sand can get inside and cause unnecessary wear to the joint. The boot also helps keep the joint well-lubricated, and any damage risks draining the grease. If the CV joint dries out, it will likely be damaged very quickly, as metal grinding on metal in a high-friction situation will wear down much faster without the protective barrier of grease.
A good rule of thumb is to inspect the CV boot every time you're performing any maintenance work under the hood. This way, you'll be able to spot wear early and prevent damage to the joint. If you don't catch a problem with the boot, a joint that is not properly lubricated can break down within just a few thousand miles.
There are a few signs that a CV joint is failing. To determine if the joints might be worn, take the car for a test drive. You may notice excessive vibrations during acceleration or hear humming sounds or an audible clunk when you speed up or slow down. Turning the car could also be accompanied by grinding or clicking noises. These sounds and sensations could also indicate other bearings are worn, the tires need to be balanced, or other issues are at play.
If these signs are not present, the joints are likely in good health, but this doesn't mean the boots are in perfect condition. If you're unsure where the CV joints are located, consult the owner's manual. Once you track them down, and the engine is off and cooled down, visually inspect the boots for signs of tears, cracks, nicks, roughness or flaking. If you notice the rubber part is at all worn, replace it. When this is done, it is important to remove the CV joint and check it for any signs of wear as well, just to be safe.