The Constant Velocity (CV) boots should be checked for aging and damage each time the oil is changed and when performing maintenance service. These boots are found at the inner and outer ends of the front drive axles of the 4 wheel drive BMW 325iX model and at the inner and outer ends of the rear drive axles of the BMW models covered in this manual. The boots are cone shaped and pleated, similar to an accordion. Because the differential is mounted to the vehicle, the axle must be able to rotate and pivot at the same time, hence both ends of the drive axle are fitted with a CV-joint. The CV-boot retains the grease used to lubricate the joint, and to prevent debris and contaminants from entering the joint. If the boots are punctured or split open, the centrifugal force of the spinning axle and CV-joint assembly will allow the grease to escape and the CV-joint will be permanently damaged. If the CV-boot is replaced before the CV-joint is damaged, the joint can be cleaned, repacked with grease, and reused. The cost of the CV-joint, is on average, about 5 to 10 times more expensive than just a boot. In some cases, the entire axle may have to be replaced. If a CV-boot failure occurs, replace the boot immediately. Signs of a CV-boot failure include the presence of heavy grease thrown around the inside of the wheel(s) and on the brake caliper/drum. Thoroughly check the boots for missing clamps, tears and deterioration. The boot is far less expensive to replace than the joint it protects. Please refer to Section 7 for repair procedures.