What’s a universal joint?

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A universal joint, also known as a U-joint, connects two rods and allows them to bend in any direction while rotating. It was first conceived by Gerolamo Cardano in the mid-16th century and has several variations. The joint is prone to wear and tear and can cause a vehicle to become inoperable if it fails. However, it is a relatively inexpensive repair and can be done by a moderate amateur mechanic with instructions available online.

A universal joint, or U-joint, is one of many names given to a type of universal joint that connects two rods and allows them to bend in virtually any direction as they rotate. Other names for the design include universal joint, which is the common term in Europe; the now archaic Hooke joint; and the Hardy-Spicer joint, named after a pair of inventors who developed a variation on the traditional design. A universal joint is typically used in situations where long shafts rotate in place and transmit power, such as an automobile transmission.

The idea of ​​a gimbal that takes advantage of the way gimbals work has been around since the classical eras of ancient Greece and Rome. Its application in motion transfer, as used in modern vehicles, was not conceived until the mid-16th century by the Italian scientist Gerolamo Cardano, for whom the joint is still named in Europe. Others later perfected the design and in the 16th century several variations were patented and remain familiar in the 19th century.

The joint of a gimbal can be modeled using the thumb and forefinger of each hand. First, make a letter U with each thumb and forefinger and join, but not touching, perpendicularly, with one set facing vertical and the other facing horizontal. Then, as if an imaginary ball were held at four distinct points, you can emulate the wide range of motion a gimbal is capable of, by moving your hands side to side and up and down.

In real U-joints, the U-shape at the end of each rod is created by forking the end of each piece of metal, like a trident that is missing the central tooth. These pieces connect to a disc that has round studs that come out at four equal points around its circumference. The studs connect to the ends of each U and become the pivot points for the joint.

While highly versatile and effective in a wide variety of applications, universal joints suffer from a propensity to wear out quickly. This is because they are in constant use whenever a vehicle is in operation. A properly functioning u-joint should have only a minimal amount of excessive movement or play. In a passenger or commercial vehicle, excessive play is often indicated by a loud rattling noise when shifting into gear and noticeable vibration at low speeds.

U-joint failure will render a vehicle inoperable, so any unusual sounds coming from underneath the cab should be checked out by a mechanic as soon as possible. A universal joint replacement is typically not a hugely expensive repair, as vehicle drivetrains are easily accessible and replacement parts are reasonably inexpensive. In fact, it’s considered a do-it-yourself repair for the moderate amateur at-home mechanic, with instructions available on the internet and in guides.




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