CV Axle

📖 YOUCANIC Automotive Glossary

CV Axle (Constant Velocity Axle)

A CV (Constant Velocity) axle, also called a half shaft or drive axle, is a shaft assembly that transmits rotational power from the transmission or differential to the drive wheels while accommodating the up-and-down motion of the suspension and the turning motion of the steering. Each CV axle has two CV joints — an inner joint (connected to the transmission or differential) and an outer joint (connected to the wheel hub). The outer CV joint is a Rzeppa-type joint designed to handle larger steering angles (up to 45-50 degrees), while the inner joint is typically a tripod (plunging) type that can slide in and out to accommodate changes in axle length as the suspension travels. Both joints are packed with special CV joint grease and sealed inside a flexible rubber or thermoplastic boot that keeps grease in and dirt and water out.

A torn or split CV boot is the precursor to CV joint failure — once the boot tears, grease slings out and contaminants enter the joint, causing rapid wear. The earliest symptom is grease splattered on the inside of the wheel and surrounding suspension components. If the joint isn’t addressed, the hallmark symptom develops: a rhythmic clicking, popping, or snapping noise during turns, most pronounced during low-speed sharp turns (such as parking lot maneuvers). This noise comes from the outer CV joint and is louder when turning in the direction that loads the worn joint. Inner CV joint failure produces different symptoms — a vibration or shudder during acceleration, a clunking noise when shifting between drive and reverse, or a humming that increases with speed. DIYers should inspect CV boots regularly during oil changes — catching a torn boot early means you can replace just the boot and repack the joint with fresh grease for under $30, versus replacing the entire axle assembly for $100-300+. When replacing a CV axle, use a new axle nut (they’re typically torque-to-yield and should not be reused), torque it to specification, and stake or cotter pin it according to the manufacturer’s procedure to prevent it from loosening.