U Joint

There are many varieties of U-Joints, a few of which are incredibly complex. The easiest category called Cardan U-Joints, will be either block-and-pin or bearing-and-cross types.

U-joints are available with two hub models solid and bored. Sound hubs do not have a machined hole. Bored hubs possess a hole and are named for the hole form; round, hex, or square style. Two bored models that deviate from these prevalent shapes are splined, which have longitudinal grooves inside bore; and keyed, which have keyways to avoid rotation of the U-joint on the matching shaft.

Using the incorrect lube can result in burned trunnions.
Unless usually recommended, use a high quality E.P. (intense pressure) grease to services most vehicular, commercial and auxiliary drive shaft applications.
Mechanically flexible U-Joints accommodate end movement by using a telescoping shaft (square shafting or splines). U-Joints function by a sliding action between two flanges that are fork-designed (a yoke) and U Joint china having a hole (vision) radially through the eye that is connected by a cross. They allow larger angles than adaptable couplings and are used in applications where huge misalignment has to be accommodated (1 to 30 degrees).

Always make sure fresh, fresh grease is evident by all four U-joint seals.

Can be caused by operating angles which are too big.
Can be the effect of a bent or sprung yoke.
Overloading a drive shaft can cause yoke ears to bend. Bearings won’t roll in the bearing cap if the yoke ears are not aligned. If the bearings end rolling, they stay stationary and can “beat themselves” into the area of the cross.
A “frozen” slip assembly will not allow the drive shaft to lengthen or shorten. Each time the drive shaft tries to shorten, the load will be transmitted into the bearings and they’ll indicate the cross trunnion. Unlike brinnell marks caused by torque, brinnell marks that will be the effect of a frozen slip are generally evident on the front and back floors of the cross trunnion.
Improper torque on U-bolt nuts can cause brinelling.
Most manufacturers publish the recommended torque for a U-bolt nut.
Improper lube procedures, where recommended purging is not accomplished, can cause a number of bearings to be starved for grease.