Driveshafts and CV Joints

A Hooke's (Cardan) joint is two yokes linked by a cross on needle bearings. At a working angle β the output speed is not constant: ω₂/ω₁ = cos β / (1 − sin²β sin²θ), where θ is input rotation angle, so output speed swings between ω₁ cos β and ω₁ / cos β twice per revolution. At 10° the fluctuation is about ±1.5%, enough to cause vibration at speed. Propshafts cancel it by using two joints with equal working angles and in-phase yokes, so the second joint's fluctuation undoes the first. A slip yoke on splines accommodates length change; long propshafts are split with a centre bearing, and some use rubber flexible couplings.

Constant-velocity joints transmit uniform speed at any angle because their driving contact points always lie on the plane bisecting the angle between the shafts. The ball-type (Rzeppa) joint has six balls running in grooves between an inner race and an outer bell, held in that bisecting plane by a cage; it is used at the wheel end where up to about 45–50° of articulation is needed. Plunging joints at the gearbox end — tripod (three rollers on a spider running in a grooved housing) or double-offset ball types — allow axial travel as the suspension compresses, at smaller angles.

Joint life depends on lubrication and angle. Boot damage admits water and abrasive dirt; the ball tracks pit and wear, producing the knocking or clicking felt most under load at large steering angles. Worn plunging joints tend to cause vibration under acceleration rather than clicks. Half-shafts of unequal length on transverse engines cause different joint angles and twist stiffness on each side, one source of torque steer.