Though rear-wheel drive remains the drivetrain layout for pickup trucks and most sports coupes and sedans, front-wheel drive (FWD) is the most common layout for the majority of passenger cars, minivans and crossover vehicles (CUVs). One of the requirements of FWD is that the axle shafts (called “halfshafts”) have inboard and outboard “constant velocity” (CV) joints. CV joints allow the shaft to rotate at a constant speed regardless of the joint angle. Ordinary universal joints (U-joints) can’t do that because as the angle of the joint increases, so does the speed of the shaft causing annoying vibrations. Also, the outer joints have to provide up to 45 degrees of movement so the front wheels can be steered. U-joints can’t handle that much deflection.
CV joints are capable of lasting upward of 150,000 miles with normal driving. But, if the protective rubber or plastic boot that surrounds the joint cracks, tears or comes loose because of a broken boot clamp, the CV joint is at severe risk of failing. A boot leak allows grease to escape and outside contaminants to enter the joint. This may damage or destroy the joint within a few hundred to a few thousand miles. So it is important to inspect CV joint boots regularly and to replace any boots or boot clamps that are damaged, leaking or missing ASAP!
The classic symptom of a worn outer CV joint is a clicking or popping noise when turning. The joint usually remains silent when driving straight ahead. Worn inner CV joints typically produce a “clunk” or shudder when the transaxle is put into gear or when the vehicle is starting out from a stop. Worn inner joints also can cause driveline vibrations that come and go at various speeds.
If a CV joint is making noise or vibrations, it is worn or damaged and needs to be replaced. If a boot has failed and the joint is still silent, it may only need a new boot provided the grease inside still feels smooth and has not been contaminated. CV joints can be disassembled for inspection, but doing so requires removing the halfshaft, removing the joint from the shaft, taking it apart and cleaning it to inspect the balls, cage and races for wear or damage. If it only needs a boot, make sure the joint is packed with CV grease, never ordinary chassis grease.
If a CV joint has failed, you can offer your customer several options: a new or remanufactured replacement CV joint, or a complete halfshaft assembly with new or reman joints on the ends. Shafts are by far the most preferred repair method because shafts are much faster and easier to install than individual CV joints. There also is less chance of a comeback with a preassembled shaft.
DIY customers who are replacing a CV joint or halfshaft will usually need some type of hub puller to separate the outer end of the CV joint and shaft from the steering knuckle.