Universal Joint

A universal joint, also known as a U-joint, is a mechanical component that is used to connect two driveshafts together.
A universal joint is necessary because it allows the transmission and differential to be offset from each other, which is necessary for the drivetrain to operate correctly. It also allows the wheels to turn while still receiving power from the engine.
A universal joint may need to be replaced if it becomes damaged or worn over time, which can cause a variety of symptoms such as clunking noises, vibration, or difficulty shifting gears. However, replacing a universal joint is a relatively minor repair that is typically straightforward and can be done quickly.
The universal joint is located in the drivetrain, typically between the transmission and the driveshaft. It is also located between the driveshaft and the rear axle on vehicles with rear-wheel drive.
The universal joint works by using a pair of yokes that are connected by a cross-shaped piece of metal called the spider. The yokes are attached to the two shafts that need to be connected, while the spider allows the joint to rotate while still transmitting power. As the shafts rotate, the spider moves around and allows for some flexibility in the joint, which is what allows it to operate at an angle.