What Could Happen if You Drive a Car With a Bad CV Joint?

Most automobiles that use constant velocity joints use at least two of them: one on the inside, near the transaxle, and another on the outside just behind the wheel hub. An axle shaft connects the two. The inner CV joint is usually a simple "tripod" design that permits enough movement to allow the suspension to go up and down without binding. The outer CV joint -- usually a more complex Rzeppa joint -- is under a lot more stress, tasked not only with handling suspension movement, but doing so while allowing the wheels to turn.

CV joints maintain very tight internal tolerances, generally close enough that only grease will fit within them. If the CV joint wears excessively, then those tolerances will open up and allow the wheel and transmission output to spin at slightly different speeds. When the two do engage, one hammers on the other and imparts an impact force onto it. Inner CV joints exhibit a fairly standard set of symptoms when they wear, tapping or clunking when a driver hits either the brake or the gas. In more extreme cases, the inner CV joint may rap or pop when the driver hits a bump. At that point, the joint is thoroughly hashed.

Outer joints will typically manifest with the same symptoms as inner joints, with one exception: Because the outer joint also bends to permit steering, it'll pop and snap more when a driver turns the wheel. Turning the wheel puts more lateral stress on the joint, which twists its internal components out of shape and causes them to bind. Inner CV joints may also pop a bit when you turn the wheel, but not nearly as much as outer joints.

A car's inner steering wheel (the left wheel in a left turn, the right in a right turn) turns at a sharper angle than the outer wheel, which puts more stress on the joint. If the tapping is louder when you turn left than right, then the bad joint is on your left-front. When testing for the CV joint, make sure to drive in very slow circles in an empty parking lot; otherwise, you'll end up transferring some of the car's weight to the other joint and confusing the test.

Continuing to drive a car with a bad CV joint will ultimately lead to complete axle failure. The hammering impact forces in the initial stages of failure will eventually break the joint outright, at which point it is only held together by the rubber dust boot. The dust boot will hold it together for a little while, but most automotive differentials will route power through the twisty CV joint rather than through the one on the other side. This will eventually either cause it to slip on the axle shaft or rip it in two. The former will leave you stranded on the side of the road, while the latter will leave your axle in the road after you run over it.