What is the Universal Joint in Automobile?

A universal joint in an automobile is the mechanical component that drives or directs the torque at different angles. It is especially a U-joint, that connects two shafts or rods at an angle to transmit torque and rotational motion between them. In this article, I will discuss the topic of “Universal joint in automobiles”


Universal Joint in Automobile

A universal joint in an automobile is used where two shafts are connected at an angle to transmit torque. In the transmission system of a motor vehicle, the transmission main shaft, propeller shaft, and differential pinion shaft are not in one line and hence the connection between them is made by a universal joint.

One universal joint is used to connect the transmission main shaft and the propeller shaft, another universal joint is used to connect the other end of the propeller shaft and the differential pinion shaft. Thus, the connections between the three shafts are flexible and at an angle with each other. The universal joint permits the torque transmission not only at an angle but also while this angle is changing constantly.

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A simple universal joint consists of two Y-shaped yokes, one on the driving shaft and the other on the driven shaft; and a cross-piece called the spider. The four arms of the spider, known as trunnions, are assembled into bearings at the ends of the two shaft yokes. The driving shaft and the driven shaft are at an angle to each other, the bearings in the yokes permit the yokes to swing around on the trunnions with each revolution.

It is to be noted that a simple universal joint does not transmit the motion uniformly when the shafts are operating at an angle, except in a constant velocity type universal joint. Because the pivot pins do not revolve in the same plane, the driven shaft will increase to a maximum and decrease to a minimum twice in each revolution. Although the degree of variation is small, however, it may be minimized by the use of two universal joints. The two joints are arranged so that the non-uniform rotation of each joint tends to neutralize that of the other.

Universal Joint in Automobile Diagram


Types of Universal Joints

The universal joints may be of three types as follows :

  1. Cross-type or spider and two-yoke type.
  2. Ball and trunnion type.
  3. Constant velocity type.

Cross-type or Spider and Two-yoke type




The cross-type universal joint is shown in Fig. 30.7. Because it consists of a cross piece or spider and two yokes, therefore, it is known as a cross-type or spider and two-yoke type universal joint. There are four needle bearings, one for each trunnion of the spider. The bearings are held in place by rings heat drop into undercuts in the yoke-bearing holes. One commercial design of the cross-type universal joint incorporates a slip joint. One yoke is integral to the hub that holds the female end of the slip joint.

When the joint is used between the propeller shaft and r .are axle gear shaft, the slip joint is omitted so that a direct connection is made between the two units. Other designs of cross-type universal joints are ring and trunnion type used in torque tube drive, and cross ball t]vp e used in Rotch-kiss drive.

Ball and Trunnion Type


The ball and trunnion-type universal joint consists of a ball head fastened to the end of the propeller shaft through which a pin is pressed. Two steel balls fit over the ends of the pin. The ball retains the roller bearing between it and the U-shaped channel in the body. The centering bottoms and the button spring help to keep the pin properly centered.

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The universal joints and propeller shaft assembly are bolted to a companion flange with the gasket and grease cover between them. The companion flange (not shown) is splined to the other shaft. The rotary motion is carried out through the pin and balls. The balls can move back and forth in the channels of the body to compensate for varying angles of drive at the same time, they act as slip joints by slipping into or out of the channels.

Constant Velocity Type


The constant velocity universal joint consists of two individual universal joints linked by a ball and socket. The ball and socket split the end of the two propeller shafts between the two universal joints. The type of joint permits uniform motion. Because the two joints are operating at the same angle, the acceleration resulting at any instant from the action of one universal joint is canceled out by the deceleration of the other and vice versa.

The function of Universal Joint

The universal joint in automobile is used to transfer the torque in various directions. In an automobile system, the universal joint is used in the propeller shaft basically because the torque needs to transfer to the wheels from the transmission shaft.

The main function of the universal joint is to transfer the torque, but the universal is used to withstand the pressure and the length of the propeller shaft. In a car, the wheels may move up and down as they encounter bumps and irregularities on the road. Universal joints allow for this movement while maintaining a consistent power transfer.

Universal joints can transfer power between shafts that are not in line with each other, making them especially useful in applications where space and geometry constraints limit the use of straight-line shaft connections. These joints can help dampen vibrations and shocks, which is important in automobiles to provide a smoother and more comfortable ride for passengers.

Advantages of Universal Joints

The advantages of the universal joints are –

  1. These types of joints are flexible, and they can transmit the torque.
  2. U-joints can accommodate misalignment between connected shafts, reducing the need for precision alignment and providing some tolerance for variations in the shafts’ positions.
  3. Universal joints can help dampen vibrations and absorb shocks.
  4. Universal joints allow for the articulation of axles, which is crucial for off-road vehicles and four-wheel drive systems.
  5. Compared to some other mechanical coupling methods, U-joints generate less heat during operation.
  6. When properly maintained and lubricated, U-joints can have a long service life, contributing to the reliability of the systems in which they are used.


The universal joints are the joints that can transmit the torque in various directions. The universal joints also help to absorb the shock coming out from the road. The U joints also help to adjust the length of the shaft when transmitting the torque. But in this system, some power loss happens due to the movement of the extra mechanical part.

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