CV joint, its full name is constant velocity joint, is an important part of a drive shaft. The function of CV joint is to bend in any direction while the wheel is running at a constant velocity, and it is mostly used in the drive shaft of front wheel drive cars. While how do you know if it is breaking? To confirm if the joint is broken, please take the car for a test drive. If you hear humming sounds of an audible clunk when you speed up or slow down, it is the sign that the cv joint is breaking. Replace it as early as possible. View more option of good cv joints, lower ball joints.