A half shaft is essentially a drive axle, and it’s so named because it does half of the job, extending from a transaxle or differential to one of the wheels. Its twin on the other side completes the set. Because they’re simply shafts, half shafts age well, but the joints that connect them on either end in independent suspension vehicles are subject to significant wear. The most prudent maintenance for these systems is to maintain the integrity of the CV joint boots, which are rubber sleeves around the constant velocity joints. The boots keep grease in and debris out. A torn or missing boot allows for accelerated wear.