• The CV joint allows the axle to spin while the wheel hub can react freely to road conditions.Car Brake image by Joelyn Pullano from Fotolia.com
  
  CV (constant velocity) joints are articulated connections between the spinning drive axles and wheel hubs on vehicles. A CV joint allows the wheel and tire assembly to fluctuate up and down with the suspension while the axle continuously turns. The CV joint is an engineering contradiction--it sustains tremendous stress under operation but can be quickly damaged if exposed to dirt or other contamination. Unfortunately, a damaged CV joint cannot be repaired; the CV joint assembly must be replaced.
  
  

Boot Contamination

• The CV boot is a ballooned rubber sleeve encasing the CV joint assembly. The boot seals the CV joint and prevents contamination (dirt, water or any type of lubrication solvent such as gasoline) from entering the CV joint. As the CV constantly rotates and articulates while in operation, the slightest grime or solvent can quickly grind away metal parts or wash away petroleum lubricants. Both problems can lead to CV joint failure.
  
  

Wear

• With increased mileage, the CV joint can wear and lose the ability to articulate through a full range of motion. The driver will notice noises from the wheels and also changes in handling. The CV joint can become stiff or loose with wear, depending on the affected parts. Also, as the CV joint wears, the connections can become loose as metal works on metal. Lubrication can reduce the metal wear, but eventually, the CV joint will reach its maximum lifespan. Whenever the CV joint is replaced as a result of increased wear, the CV boot should also be replaced. The boot is composed of rubber and will dry and lose flexibility with age, decreasing its ability to protect the new CV joint.
  
  

Lack of Lubrication

• The CV joint is lubricated with grease. A port permits a grease gun for injecting lubricant into the joint without removing the boot. If the CV joint goes for too long a period without lubrication, the available lubricant will break down with use, and the moving parts will generate friction and wear. Another complication is the lubrication can be contaminated with age. Even though the metal parts are lubricated to reduce friction, small particles of metal from the CV joint itself can become suspended in the lubrication. Eventually, these particles can work back into the moving parts and lead to wear despite adequate lubrication. A regular CV joint inspection can determine if the available lubricant should be removed, the components thoroughly cleaned and clean lubricant added.