CV Joints and CV Axles

CV stands for Constant Velocity. A CV joint transmits rotational power through an angle while maintaining a constant speed of rotation — the output turns at the same speed as the input regardless of the joint angle. Without CV joints, the wheels would speed up and slow down with every rotation as the angle changed, creating a pulsing vibration that would be undriveable.

Every CV axle has two CV joints — an inner joint and an outer joint. The outer joint is a Rzeppa type — a ball-and-cage design that handles the large steering angles at the wheel. The inner joint is typically a tripod type — three rollers on a spider that slide in and out of a tulip housing. The sliding motion of the inner joint allows the axle length to change as the suspension travels up and down. Both joints are packed with special CV joint grease and sealed inside a rubber or thermoplastic boot. The boot keeps grease in and dirt out. When the boot tears, grease flings out and contamination gets in. The joint fails in a matter of weeks.

A clicking or popping noise during tight low speed turns — like in a parking lot — that gets louder as you turn tighter is the signature of a worn outer CV joint. The clicking happens because the balls in the Rzeppa joint are worn and have excess play. They shift position under load during the turn and produce a distinct rhythmic click timed to wheel rotation. If you hear it, inspect the outer boot first. If the boot is torn and the joint is clicking, the axle needs replacement. A joint that is already clicking cannot be saved by repacking — the damage is done.

A vibration or shudder during acceleration — especially from a stop — that feels like it is coming from under the vehicle often points to a worn inner tripod joint. The rollers are worn or the tulip housing is scored. Unlike the outer joint click which happens during turns, the inner joint vibration happens during straight line acceleration because that is when the most torque loads the joint.