The most common type of universal is a Hooke's joint or a cross-and-roller joint.
It consists of a steel cross with four hardened bearing journals, mounted on needle rollers in hardened caps, which locate the cross in the eyes of the yokes.
The cross swivels in the yokes as the drive is transferred from one shaft to the other. However, the swiveling conflicts with the rotation, and in each revolution the velocity of the yoke changes every 90 degrees.
This change in the angular velocity increases as the angle between the driving and driven shafts increases. This type of joint is a non-constant velocity joint.
The effect of the changing velocity can be eliminated by having identical joints at each end of the propeller shaft in phase with each other, and by having the input and output drives parallel.
An increase in the velocity of the front yoke is cancelled out by a similar decrease in the velocity of the rear yoke in each revolution.
In some cases a type of constant-velocity joint is fitted to the front end of the propeller shaft.
This Lobro joint has an inner race splined to the end of the propeller shaft, and an outer race bolted to the connecting flange.
A number of balls, retained by a spherical cage, are carried in angular grooves in each race, and these balls transfer the drive from one race to the other.
The outer race is also able to move longitudinally on the inner race grooves and this accommodates changes in shaft length.
This type of joint allows the drive to be transmitted through a greater angle and minimizes vibration.
Where the angle between the shafts is small, a flexible hard rubber coupling can be sandwiched between tripod flanges on the propeller shaft and the differential pinion.
Since no friction-producing parts are involved, noise and vibration are reduced to a minimum.
