CV Joint History
The most common type of outboard CV joint is the "Rzeppa" style. This type of joint was invented way back in 1920 by a Dana engineer named Alfred H. Rzeppa. His design allowed power to be transmitted through six spherical balls located between an inner and outer race. In this design, the balls are held in position by small windows in a cage assembly that fits between the inner and outer races. The design of the joint is such that the position of the balls always bisects (cuts in half) the operating angle of the joint. It is a slick design that works something like a bevel gear. But instead of gear teeth transmitting the torque across the joint, the balls push against their respective tracks in the inner and outer housings.
The other type of CV joint you will see is the "tripod" style joint. Tripod joints do not have balls but instead use needle bearing rollers mounted on a three-legged spider. The rollers are mounted at 120 degrees to one another and slide back and forth in tracks in an outer "tulip" housing. Tripod style joints are used for the inner joints on most FWD models from 1983 to present. This type of joint is less expensive to manufacture than a ball type joint, and is well-suited to the limited operating angles of the inner joint location. The joint is designed to plunge in and out the same as other inboard joints to allow changes in shaft length as the suspension moves.
U-joint Vs Constant Velocity joint
U-joints work fine on the driveshaft in most rear-wheel drive applications, so why not FWD too? The answer is because U-joints produce cyclic vibrations when operated at the kind of steering angles found in a FWD application. Ordinary Cardan type universal joints cause a change in speed between the driving and driven shafts whenever the joint operates at an angle. As the operating angle of the joint increases, the speed (velocity) of the driven shaft varies more and more during each revolution of the shafts. The greater the operating angle, the greater the variation in speed of the driven shaft and the greater the vibration it produces. The driven shaft still turns at the same number of revolutions per minute as the shaft that is driving it, but because of the geometry of a universal joint the speed of the driven shaft alternately increases (accelerates) and decreases (decelerates) four times every revolution, and this is what causes the vibrations we are talking about.
The speed changes are not great when the angle is less than a few degrees, but as the operating angle of the joint increases so do the cyclic vibrations of the driven shaft as well as the back and forth motion in the joint itself. The changing rotational velocity of the driven shaft can be offset by installing a second U-joint on the opposite end of the driven shaft "phased" 90 degrees with respect to the first joint. In theory the second joint cancels out the changes in output velocity caused by the other joint, but only so long as both joints operate at identical angles.
The universal joint works fine for RWD driveshafts where front and rear joint angles are usually identical and the changes in operating angles are relatively small, but with front-wheel drive the situation is entirely different. The inner and outer joints often operate at different angles. Whenever the wheels are turned, the outer joint runs at a much higher angle than the inner joint. This upsets the offsetting relationship between inner and outer joint angles that is a necessary requirement for ordinary U-joints. The front wheels are also required to steer at angles of up to 45 degrees, which puts too much strain on a U-joint.
