The propshaft plays a crucial role in transmitting crank rotations to the differential.
Most single-piece propshafts have two (Hooke, Cardan or Hardy-Spicer) universal joints – to allow them to rotate through a varying angle.
If your car has a live axle, then it’s doing exactly that as it accelerates and decelerates many times during a journey and the suspension moves, while being exposed to heat and dirt.
On a live axle, the prop often has a splined ‘female’ union between the yoke and the gearbox’s tailshaft. If so, you’ll need to drain the ’box oil first.
UJs are typically positioned at 90º to each other in the same plane to eliminate their inconsistent speed when operating at an angle, something that constant-velocity joints were developed to overcome.
UJs comprise a cross-piece (the spider) with each axis featuring a pair of needle-roller bearings in a cap that fits into the ends of the two yokes. The caps are removable for fitting purposes, but the needle-roller bearings – held in only by grease – must not be disturbed.
Never clamp the prop on the tubular part: it’s easily distorted. Only the yoke, or the weld between the yoke and tube, is strong enough to withstand the jaws of a vice.
1: MARK AND REMOVE PROP
Prop flanges have a rectangular bolt pattern, so mark the position of the rear UJ relative to the pinion flange and each yoke relative to the shaft with paint – vital if you’re not having the prop balanced.
