Driveshafts, Half-Shafts, U-Joints, and CV Joints
Driveshafts and joints
A rear-wheel-drive driveshaft transfers torque from the transmission or transfer case to the differential. Key parts include the slip yoke, universal joints, center support bearing on two-piece shafts, and companion flanges. A U-joint does not maintain constant velocity; its speed fluctuates with operating angle. Phasing-aligning the yokes so the joints work together-cancels most of that fluctuation. A double-cardan joint is used where angles are large. Front-wheel-drive and independent rear suspension vehicles use half-shafts with constant velocity joints: an outer Rzeppa-style joint for steering angle and an inner plunge joint for length change. Boots keep grease in and contamination out.
Traps
Clicking during turns is a classic outer CV joint symptom. Vibration at road speed can be a thrown balance weight, worn U-joint, center bearing, or driveline angle problem-do not mistake it for tire balance alone. A clunk on acceleration or deceleration may be a worn U-joint or slip-yoke spline. Torn boots mean joint contamination; repack or replace. U-joint phasing errors cause vibration. Always mark shaft-to-yoke positions before disassembly.
Worked example
A single-piece driveshaft is removed for a U-joint replacement. Before pressing the joints, confirm the yokes at both ends are in the same plane. If the shaft is assembled 90 degrees out, the joints are out of phase and vibration can result. Rule of thumb: align marks; if no marks exist, phase the yokes as originally designed.