Propeller Shaft Universal Joint

The universal joint allows driving power to be carried through two points that are at angles to each other. The universal joint is a double-hinged joint consisting of two Y-shaped yokes and a cross-shaped member called the spider (2). One of the yokes is on the driving shaft, and the other is on the driven shaft. The four arms of the spider, called trunnions, are assembled into bearings in the ends of the two shaft yokes. The driving shaft and yoke cause the spider to rotate, and the other two trunnions of the spider cause the driven shaft to rotate. When the two shafts are at an angle each other, the bearings in the yokes permit the yokes to swing around on the trunnions with each revolution.

When torque is transmitted through any ordinary universal joint, the drive pinion gear yoke fluctuates slightly in speed. In other words, although the propeller shaft slip yoke (1) rotates at a constant speed, the differential drive pinion gear yoke speeds up and slows down twice per revolution. This fluctuation of the pinion gear yoke is in direct proportion to the angle through which the universal joint is operating; the greater the angle, the greater the fluctuation.

Whenever two universal joints are used, this fluctuation effect can be eliminated by staggering the joints so that the two yokes are 90° apart, provided the two joints are transmitting torque through the same angle.

Therefore, when two universal joints are used, the angles through which they operate must be very nearly the same. This allows the alternate acceleration and deceleration of one joint to be offset by the alternate deceleration and acceleration of the second joint. When the two joints do not run at approximately the same angle, operation is rough and an objectionable vibration is produced.

Universal joints are designed to handle the effects of various loads and rear axle windup during acceleration. Within the designed angle variations the universal joint will operate efficiently and safely. When the design angle is changed or exceeded, the operational life of the joint may decrease.

The universal joint bearings (3) used are the needle roller type. The needle roller bearings are held in place on the trunnions by round bearing caps. Production universal joint bearings (3) are retained by nylon injected rings instead of conventional snap rings (4). All service replacement universal joints use snap rings (4).

Factory installed propeller shaft universal joints are lubricated for life, but service universal joints have grease fittings and require periodic lubrication. If it becomes necessary to replace a universal joint, the entire propeller shaft (5, 6 and 10) must be removed from the vehicle. Care-should be taken to avoid jamming or bending any parts of the propeller shaft.