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

U-joints can be found with two hub types solid and bored. Solid hubs don’t have a machined hole. Bored hubs possess a hole and so are known as for the hole condition; round, hex, or sq . style. Two bored styles that deviate from these prevalent shapes are splined, that 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 normally recommended, use a high quality E.P. (extreme pressure) grease to provider most vehicular, industrial and auxiliary drive shaft applications.
Mechanically flexible U-Joints accommodate end movement by simply using a telescoping shaft (square shafting or splines). U-Joints function by a sliding motion between two flanges that are fork-designed (a yoke) and having a hole (attention) radially through the eye that is linked by a cross. They let larger angles than flexible couplings and are being used in applications where high misalignment has to be accommodated (1 to 30 degrees).

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

Can be due to operating angles which are too big.
Can be the effect of a bent or perhaps sprung yoke.
Overloading a drive shaft can cause yoke ears to bend. Bearings will not roll in the bearing cap if the yoke ears aren’t aligned. If the bearings quit rolling, they continue to be stationary and will “beat themselves” in u joint201909181135265136934to the surface of the cross.
A “frozen” slip assembly won’t allow the U Joint china travel shaft to lengthen or shorten. Each and every time the travel shaft attempts to shorten, the load will be transmitted into the bearings and they will tag the cross trunnion. Unlike brinnell marks caused by torque, brinnell marks that will be the effect of a frozen slide are usually evident on the front and back areas of the cross trunnion.
Improper torque in U-bolt nuts could cause brinelling.
Most manufacturers publish the recommended torque for a U-bolt nut.
Improper lube procedures, where recommended purging is not accomplished, can cause one or more bearings to be starved for grease.