The U-ioint in a Jeep is located at the end of the driveshaft
The U-joint in a Jeep is responsible for transmitting torque from the transmission to the differential.
When torque is applied to one of the shafts, it is transmitted through the universal joint to the other shaft, causing it to rotate.
U-joints allow drive shafts to move up and down with the suspension while the shaft is moving so power can be
transmitted when the drive shaft isn’t in a straight line between the transmission and drive wheels.
It’s a cross shaped piece with a bearing at each end, that allows for lateral and side to side movement of the driveshaft