Half shafts, also called intermediate shafts, serve as connection points between the trans-axle (transmission) and the drive wheels. They appear on front-wheel drive vehicles, and are sometimes used on rear wheel drive vehicles with independent suspension. Two half shafts sit on either side of the front-wheel drive transmission, with some half shafts longer than others, depending on the mounting position of the transmission. They contain connection points at the inner and outer CV (constant velocity) joints, and sometimes are supported by a carrier housing and tripod bearing. Half shafts display a number of failure warning signs that a vehicle owner can discover, by using a few testing procedures and observations.
Drive the vehicle through a normal range of speeds, accelerating and decelerating. Note any vibration in the chassis floorboard, or a vibration felt in the steering wheel. The vibration will be most pronounced upon acceleration from a dead stop. The likely cause, provided the CV joints are in good condition, will point to excessive wear in the half shaft carrier or tripod bearing.
Listen for a "clunk" when putting the transmission selector in forward or reverse gear. The cause will most likely be the inner or outer CV joint bearings, where they connect with the half shaft. If the half shaft has a rubber damper, the damper could be split, torn or partially disconnected, causing excessive play.
Listen for a humming sound while driving through all speed ranges, but particularly during acceleration from low to medium speeds. There may also be a metallic growling or swishing sound, like that of a failed bearing grinding within a bearing race.
Raise the vehicle with a floor jack high enough to place two jack stands under the rear frame and two jack stands under the front frame. Take a shop light under the vehicle and inspect both half shafts, where they join to the inner and outer CV joints. If one shaft has a carrier housing, sometimes called a "hanger," check the mounting bolts on the hanger, to see if they are missing or broken. The carrier housing should be aligned properly and have no play, fully supporting the half shaft.
Look for indications of thrown and splattered grease in the half shaft connection points to the inner and outer CV joints. Grease will appear on the trans-axle housing, firewall or on the shafts and CV joint boots. Examine the CV joint boots for any tears, or loose boot clamps. They outer CV joint boot and bearing assembly will usually wear and fail first, so check both outer CV joint boots. Wipe the boots down with rags and inspect them carefully. A torn boot will allow water and dirt to contaminate the bearing, causing excessive wear.
