Cars comprise many relatively small components that, while they might not get as much attention, are vital to safe operation. One such part is the constant velocity (CV) joint, which transmits power from the transmission to the wheels (usually the front wheels). The one little bit of protection it has is called a boot, but what is a CV boot exactly, and how do you know if yours is in trouble?
The CV joint itself basically keeps your axle from breaking every time you hit a bump, and keeps your wheels aligned and turning. There are actually two of them on an axle: one at the transmission and one at the wheel. They allow for all types of movement and any odd angles required as you pass over the road, and as such, the joint must remain very well-lubricated. The boot is a small rubber encasement that covers the joint and keeps grease packed inside.
It’s easy enough for the boot to tear, either by road debris or age. When it does, grease leaks out and contaminants like water and damaging particles make their way in. With less lubrication and more water, you’ll start to build rust, which will quickly destroy the joint. A broken CV joint is a critical failure that will render the car undriveable, so keeping an eye on your boot and replacing it soon after it’s torn should be a top priority. There are a few warning signs that you have a problem: grease splattered on the inside of the wheel, visible damage or vibration while driving. If you get a serious vibration or you hear a noticeable clicking or popping when you turn, you are already too late and should immediately get the entire CV axle replaced.
Getting the Boot
If you notice the issue while the joint is still in good condition, though, there is hope. The joint can be repacked with grease, and a new boot can be installed. There are three different options. The conventional boot is a seamless whole, which can only be installed after taking the axle out of the car. At that point, you might as well install a whole new joint. A stretch boot can be installed by removing only the wheel and hub assembly, but is slightly weaker. Finally, a split-boot design is the easiest but weakest option, which can be installed without removing any components, but doesn’t last as long.
So what is a CV boot? It’s a tiny but critical piece of a vital component in your drive train. Considering the consequences of neglecting its maintenance, it makes sense to add this to regular inspections, especially after 100,000 miles.
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Photo courtesy of Wikimedia Commons.
Blair Lampe is a New York-based professional mechanic, blogger, theater technician, and speechwriter. In her downtime she enjoys backpacking wherever her boots will carry her, rock climbing, experimental theatre, a crisp rosé , and showering love on her 2001 Sierra truck.