If you have a front wheel drive or all wheel drive car, you should check the boots. Most of these modern cars have drive axles that contain 2 rubber boots. The boots protect a component called a constant velocity joint, (or CV joint). The CV is like the old universal joints that rear wheel drive cars had on the drive shaft. The difference is that CV joints flex a great deal. They must be kept lubricated with clean grease. The drive axle has one or two CV joints. Each CV joint has a rubber boot over it for protection. The boot keeps the water out and the grease in. Being made from rubber, the boot can get hard and crack. It can also get punctured with a stick or other road debris. It is unfortunate, but the boot can fail and cause the CV joint to fail due to the grease becoming contaminated with water and dirt.

If your car is perhaps 5 or more years old, you should inspect the CV boots. Check under the front of the car. There will be a drive shaft running to each wheel from the transaxle, (or the transmission). The drive shaft will have two rubber boots clamped on it. These are typically black with accordion style pleats. The pleats let the boot expand and contract when the CV joint flexes. Take a good look at the boots. They should be undamaged and free from oil or grease. There may be a small hole in the boot, but usually bad ones are quite obviously bad. The boot might have a gaping rip in it or be completely separated into two pieces. If there is no obvious damage, check the underside of the car directly above the CV boot. If the boot has a small hole, there may be a pattern of grease that has been thrown onto this area. Any sign of damage indicates that the CV boot must be replaced. The CV joint may not have been damaged yet so there may not be obvious indications to the driver of trouble with the part. While you check the CV boot, check for other similar damage as well. Some vehicles have similar rubber boots on the steering gear. Check the car for obvious signs of oil leakage.

When the CV boot fails, water and debris are able to attack the CV joint. The CV joint is a precision piece of machinery that rotates at high speed and flexes as your car hits bumps and goes around corners. The parts are designed to fit with very small tolerances and must be lubricated with special grease. There are precision ball bearings installed in machined housings, allowing the joint to flex. Water breaks down the grease. Dirt gets into the parts and wears them out quickly. If you ever experience strange clicking noises when you go around corners, you may have damage to your CV joint due to contaminated grease. Like most car parts, the damage will not get better. Continued operation with contaminated grease will continue to damage the CV joint. In time, it will fail completely, causing loss of control of the vehicle. Usually drivers are very frustrated with the car's behavior long before the CV joint is completely destroyed. As the CV joints wear, they allow the drive axle to travel too much which will begin to affect the tires, wearing them out quickly. This also upsets the alignment of the car. Tire wear and alignment problems will affect gas mileage making the car more expensive to operate. In addition to damage and car trouble, if the CV boots fail, the grease will be lost. This introduces it as a pollutant into the environment. Like all leaks of oil or grease, they should be repaired quickly to minimize the effect on the environment.

Unfortunately, the CV boot is quite a difficult part to replace. It is fastened onto the drive shaft with special retaining clamps. To get them off, the entire drive shaft must be removed. The clamps are cut off. New clamps are installed using a special tool. The weight of the car must be taken by jacks. When the CV joint is exposed, it must be totally cleaned and lubricated with new grease. All of this effort takes time and is usually not a job to be attempted by the car owner. With labor being an expensive item at automotive shops now, it is often an option to completely replace the drive axle rather than replace the boots. This saves a substantial amount of labor. The new part already comes with installed boots that protect the CV joint and the grease. A mechanic can lift the car, remove the drive shaft and install a new one in a short amount of time. The new drive axle is usually guaranteed for a length of time against failure or bad CV boots. While the cost of a new, or rebuilt, axle is much more than the rubber boots, the savings in labor charges is the main consideration. As well, the new axle has been tested by a specialty parts manufacturer. There is no need to inspect the new CV joints on a replacement drive shaft. (Since the new drive shaft comes with new boots, it is also not possible to inspect the CV joint.)

Car maintenance is an expensive item and many people are surprised to find out that they have rubber constant velocity joint boots that need to be replaced. These parts operate in a harsh environment, as has been mentioned above. With more people keeping their cars longer these days, increased maintenance costs are to be expected. The CV boots are special rubber parts that do a good job of protecting the CV joint from most water and dirt on the road. Being rubber, (or neoprene), they can deteriorate over time. They are also fairly thin so sticks and debris can rip holes in them. It is estimated that over 10 million drive shaft repair jobs are performed in a typical year. This figure should go up in time due to the aging of cars on the road.