The final link in your engine's power journey from the crankshaft to the rear wheel is your BMW Axle. Each BMW axle--there are two on rear-wheel drive cars, and four on all-wheel drive vehicles--transmits torque from the differential out to the driven wheel. Since the suspension fits in somewhere between the two, it stands to reason that the axle would have to permit at least up and down movement. In the case of an all-wheel drive vehicle, the BMW axle also has to permit movement around the steering axis as well. The complex, multi-joint axles in your modern sports sedan are a far cry from the live axles in old American vehicles.

BMW axles generally have two constant-velocity joints along the shaft that permit a full range of motion while still transmitting full torque. When your BMW axle wears out, it's usually these constant-velocity joints that have deteriorated, causing clunks and clicks as they operate. In worst-case scenarios, a CV joint can actually come apart. Fortunately, this isn't a frequent occurrence, and diligent maintenance will keep your BMW axles rolling smoothly for tens of thousands of miles.