The front Nissan CV axle shafts are the drive components that power the wheels with motion. These axle shafts by their nature are more flexible than the older style solid axles, but that makes them more vulnerable to being worn out over time. The CV axle shafts are on all type of vehicles that have an independent suspension on its drive wheels. They receive their power from the pair of intertwining yokes around a U-joint or by a Rzeppa-style ball and cup joint. It is this union that is the weak link in this drive system. If the CV axle shaft on your Nissan has been properly maintained, then the CV boot will still be in place. This is important since it is this boot that keeps the grease packed in around the CV joint keeping it lubricated so the wear on this drive component is kept at a minimum. When a knocking sound is heard from the wheel assembly of your Nissan, the noise would be coming from the joint connected to the CV axle shaft. This is an indication that this drive component will be in need of replacement. If the wear on the Nissan CV axle shaft becomes so great that it breaks, the damage to the surrounding components will be severe. It will also cause a complete lack of steering control; ultimately resulting in an accident. The best way to keep the CV axle shaft properly lubricated on your Nissan is to make sure the CV boot is not damaged. If it is torn, it should be immediately replaced so the CV joint will not be affected in a negative fashion.