CV joints allow a shaft to rotate and transmit power. CV joints have to be kept lubricated to avoid friction. The CV boot protects the joints in the center of the wheel connected to the drive shaft. It looks something like the rubber end of your plunger. This keeps the joints free of debris.
When to replace CV joint?
Maneuvering the vehicle will be harder once these are damaged. A clicking noise beneath the car every time you turn the steering wheel is a sign that the CV joint is bad. Other signs that the CV joint needs to be replaced is a vibration in your vehicle when accelerating. Also a clunking sound that happens when the gears on your vehicle change. When changing gears, you will notice a hesitation followed by a clunk noise. To test, accelerate and decelerate in reverse, this will make the noise more pronounced. As long as a CV joint remains sealed inside its protective environment it will do its job until it wears out.
When to replace CV boot?
If you notice a tear or that they are out of position then that is a sign the boot needs to be replaced. Split, cracked, loose or torn boots will throw grease draining the joint of its vital supply of lubricant. If the boot is bad it can cause the joints to dry out. If found early enough the CV boot may be able to just be replaced and the joints re-lubricated.
Checking the CV joints and boots should be a part of every oil change, brake replacement, alignment and every suspension repair. CV joints are typically being replaced anywhere from 70,000 miles to 130,000 miles under normal operating conditions. Failure to replace a failing CV joint is very dangerous, it can fail at high speeds putting yourself, passengers and others at risk.