Commonly replaced driveline parts include CV joints/FWD axle shafts, U-joints and wheel bearings.
CV joints come in various types. Rzeppa, crossgroove and double-offset CV joints have six small balls housed between and inner and outer race. Rzeppa CV joints are most often used as outer joints.
Crossgroove and double-offset joints “plunge” in and out to accommodate length changes in the halfshafts as the suspension moves up and down and are often used as inner joints on halfshafts. Tripod joints contain no balls but have three roller bearings mounted inside a “tulip” or “claw” shaped housing. Tripod joints may be fixed or the plunge variety. Tripod CV joints are mostly used as the inner plunge joints on domestic FWD applications, but also may be used as outer joints on some older import applications.
CV joint failures can be the result of high-mileage wear, loss of lubricant or outside contamination. Replacing a leaky or damaged CV joint boot is often a waste of time because damage has already occurred to the CV joint.
A failing outer CV joint will usually make a clicking or popping sound when turning. A bad inner CV joint may clunk or vibrate when accelerating. CV joints may be replaced separately or as part of halfshaft assembly. It’s usually easier and faster (and sometimes even cheaper) to replace the entire halfshaft or axle assembly than to replace an individual CV joint. Replacement shafts must have the same overall length as the original, with identical splines and end dimensions. On vehicles with ABS, the ABS wheel speed sensor tone rings on the shaft or outer CV joint must also be identical.
U-joints are used on the ends of the driveshafts in most rear-wheel drive cars and many four-wheel drive trucks. A worn U-joint may cause a vibration at speed or make chirping noises, or clunk when putting the transmission into gear.
Most original equipment U-joints are sealed, but some have grease fittings to accept chassis grease. A U-joint failure may allow the driveshaft to fall out of the vehicle. Replacing a U-joint requires removing the driveshaft and pressing the old joints out of the driveshaft yokes, and pressing in the new joints. Both joints should usually be changed at the same time. If the vehicle has a two-piece driveshaft with a center carrier bearing, the carrier bearing also should be replaced.
Most late-model wheel bearings are part of a sealed hub assembly or a sealed cartridge. Sealed bearings require no maintenance or adjustments. Replacement is needed when the bearings become worn, rough or noisy. On vehicles with ABS, the wheel speed sensor may be part of the hub and bearing assembly. If the sensor fails, the entire hub must be replaced.