As a follow-up on the hugely popular video on driveshaft and u-joint operation, here’s a great little animation that shows how constant-velocity joints work. 

We were a little surprised but gratified by the enormous response to the recent video on driveshafts and universal joints. We learned a couple of things there. First: Mac’s Motor City Garage readers are true gearheads with a genuine interest in the nuts and bolts of automotive technology. Second: Solid technical info presented in a simple, non-nonsense manner is always in demand.

The chief takeaway from the video was that standard, cross-type universal joints (formal names include Hooke’s joint and Cardan joint) do not rotate at constant velocity. Rather, they vary in speed according to angle and phasing, which places limits on their installation and use.

However: There’s another, more elaborate type of coupling, known as a constant-velocity joint or CV joint for short. And as the name indicates, this type of joint produces a more uniform rate of motion, which makes it useful in more demanding applications—the driving and steering axles of front-wheel drive cars, for example.

While there are many variations on the basic theme, the most familiar form of CV joint is known as the Rzeppa joint, after its inventor, Alfred R. Rzeppa. By the way, Rzeppa was one of the great unsung engineering minds of the early Motor City. His company, the Gear Grinding Machine Company of Detroit, generated numerous innovations and spin-off businesses, from high-precision machine tools to tandem truck axles to sprag clutches for automatic transmissions.

In the Rzeppa-style universal joint, torque is transferred from an inner race to an outer race by a concentric cluster of spherical bearings, producing constant shaft velocity through a greater range of articulation…. let’s stop right there. This is another case where showing is far more effective than telling. Video below.