What is a Universal Joint? A Complete Guide

A universal joint – also called a universal coupling, U-joint, Cardan joint, Spicer joint, Hardy-Spicer joint, or Hooke’s joint – is a mechanical device that connects two rotating shafts, allowing them to transmit power even when they are misaligned.

How Does a Universal Joint Work?

A U-joint consists of two revolute joints with perpendicular and intersecting axes. Each shaft ends in one of these joints, with its axis perpendicular to the shaft’s rotational axis. This configuration:

• Transfers rotary motion between misaligned shafts

• Allows relative rotation in two axes

• Constrains one rotational degree of freedom (shaft rotation) and all translations

• Provides two degrees of freedom (2-DOF)

Key Characteristics and Limitations

Not a Constant-Velocity Joint
If the input shaft rotates at a constant velocity, the output shaft’s velocity will oscillate – faster and slower through each revolution. The shafts have the same average velocity, but instantaneous velocities differ. The greater the misalignment angle, the more pronounced this velocity fluctuation becomes.

Creating Constant Velocity
A double Cardan joint uses two U-joints with a short connecting shaft, 90° out of phase. When the bend angle is equally shared between them, velocity oscillations cancel out, creating constant velocity at the output. However, the intermediate shaft still oscillates, requiring proper support to maintain equal angles and minimize vibration.

Applications and Current Use

While universal joints were once widely used in vehicle drivetrains, they’ve been largely replaced by constant velocity joints in front-wheel drive applications. Today, U-joints remain common in:

• Drive shafts (particularly for trucks and heavy equipment)

• Heavy-duty off-road vehicles

• Industrial machinery

• Mechanical control systems

Their ability to handle large angles between shafts makes them valuable for many power transmission applications. For slight misalignments, flexible couplings often provide a simpler alternative.

Why Choose Apex Coupling for Universal Joint Solutions?

At Apex Coupling, we provide robust universal joints engineered for demanding applications. Our U-joints offer:

• High torque capacity for heavy-duty use

• Durability in challenging environments

• Precision manufacturing for smooth operation

• Custom solutions for OEM/ODM requirements

Whether you need reliable U-joints for vehicle drivetrains, industrial equipment, or specialized machinery, we have the expertise to deliver optimal power transmission solutions.

Ready to solve your power transmission challenges? Contact Apex Coupling today for expert guidance and custom universal joint solutions.