There are many varieties of U-Joints, some of which are incredibly complex. The simplest category known as Cardan U-Joints, happen to be either block-and-pin or bearing-and-cross types.

U Joint china U-joints can be found with two hub variations solid and bored. Sturdy hubs don’t have a machined hole. Bored hubs include a hole and so are called for the hole shape; round, hex, or square style. Two bored designs that deviate from these prevalent shapes are splined, which have longitudinal grooves inside the bore; and keyed, which have keyways to avoid rotation of the U-joint on the matching shaft.

Using the wrong lube can cause burned trunnions.
Unless or else recommended, use a superior quality E.P. (intense pressure) grease to assistance most vehicular, professional and auxiliary travel shaft applications.
Mechanically flexible U-Joints accommodate end movement simply by utilizing a telescoping shaft (sq . shafting or splines). U-Joints function by a sliding action between two flanges that are fork-designed (a yoke) and having a hole (eye) radially through the eye that is connected by a cross. They enable larger angles than adaptable couplings and are being used in applications where high misalignment needs to be accommodated (1 to 30 degrees).

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

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