A CV axle assembly is a drivetrain component on a vehicle that delivers power from the transmission to the wheel. It is commonly used in front-wheel-drive systems, but can also be found on all-wheel-drive, and even some rear-wheel-drive vehicles with independent suspensions. A CV (constant velocity) joint is fitted near each end of the axle assembly.
How does a CV Joint work?
The CV axle runs between the transmission and the wheel hub and features a CV joint located at each end of the axle shaft. These joints allow movement to accommodate the many angles that the axle faces as part of a front wheel drive system. The CV joint is a type of universal joint, housed in a cup that lets it slide in and out and flex in multiple directions - all while the axle is spinning. That way, it can travel over bumps in the road with the suspension, while at the same time it can turn with the steering.
A "clicking" noise when turning can be from a failing CV joint. In many cases, the CV axle shaft will need to be replaced.
What are the symptoms of a bad CV Joint?
The CV joints are lubricated with grease and sealed inside a pair of rubber boots. These boots hold the grease inside, and they keep the dirt and grime outside. Otherwise, the CV joints would deteriorate rapidly. But, over time, the boots can become worn and can crack or tear. Some of the grease escapes and dirt enters the joint, causing it to break down. When this happens, the CV joint develops excessive play in its bearings. A repetitive clicking sound may be heard when the vehicle is accelerating through a curve - such as on a freeway entrance ramp. A clunking sound may be noticed upon deceleration. Vibration may be felt when traveling at highway speeds. A visual inspection of the CV axle shaft will usually reveal grease seeping from a crack or tear in one of the boots.
Can I drive with a bad CV Joint?
As a CV joint begins to deteriorate, and symptoms start to appear, the vehicle is still driveable. Once the process of breakdown in the CV joints begins, however, it does not reverse. The problem will continue to worsen. If left for too long, a CV joint can break apart, causing considerable damage to the steering and suspension and possibly a loss of control of the vehicle. At the least, the vehicle will be undrivable. The axle should be repaired or replaced sooner than later - before it fails.
How often do CV Joints need replacement?
A CV joint should last the lifetime of the vehicle. Unfortunately, it is not uncommon for an axle to fail. If a CV joint boot cracks or tears, it is only a matter of time before the joint wears out. If a boot is compromised, it can be replaced. If the problem is recognized before other symptoms happen (clicking or clunking sounds when driving), the life of the axle can be prolonged. Replacement of the joints and boots on a CV axle requires that the entire assembly must be removed from the vehicle and disassembled. Because of this labor-intensive approach - and because there is no guarantee how long the joint may last after being compromised - many owners choose to have the entire assembly replaced instead.
How are CV Joints diagnosed?
To diagnose a failing CV joint, a technician will remove the wheel and inspect the CV joint boots for wear and cracks. If the boots are damaged, replacement is indicated. If no visible signs of wear appear, it may be necessary for the technician to take the vehicle for a test drive to evaluate the symptoms. Sometimes a damaged CV joint is noticed during other repairs or inspections.
How are CV Joints replaced?
To replace a CV joint, a technician will need access to vehicle-specific repair information. The means of connection between the axle and the transmission differs from one model to the next. For instance, some axles feature a hidden snap ring that retains the axle inside the transmission. The technician will lift and support the vehicle and pull the wheel and tire. The axle nut is removed and the lower control arm ball joint is disconnected so that the wheel hub and steering knuckle can be moved out of the way. The outer end of the axle is pushed through the wheel hub to release it from the front suspension and steering. The axle assembly is supported to avoid damage to the oil seal between the transmission and the axle, and the axle is disconnected from the transmission. Once outside the vehicle, the axle is disassembled, fitted with new boots and new joints, and packed with grease. The rebuilt axle assembly is fitted into place, and the front suspension and steering components are reinstalled. Finally, the hardware is torqued to manufacturer's specifications and any lost fluid is replaced. On some vehicles, additional disassembly of suspension parts might be necessary.
A CV joint can be damaged as a result of the loss of grease due to a damaged boot. If the CV joint is "clicking" while the vehicle is turning, the CV joint and/or axle should be replaced.
RepairPal Recommendations for CV Joint issues
RepairPal recommends the use of new replacement CV axle shafts. It is increasingly economical to do so, and new axle assemblies are more reliable than rebuilt units. In addition, there is little advantage to replacing the CV joint boots. The cost of repair is nearly as much as the cost of a new axle, and there is no guarantee that permanent damage has not already been done to the joint.
