There are many varieties of U-Joints, some of which are incredibly complex. The easiest category called Cardan U-Joints, happen to be either block-and-pin or bearing-and-cross types.
U-joints can be found with two 
hub designs solid and bored. Sound hubs don’t have a machined hole. Bored hubs own a hole and so are named for the hole form; round, hex, or square style. Two bored models 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 lead to burned trunnions.
Unless usually recommended, use a high quality E.P. (intense pressure) grease to program most vehicular, industrial and auxiliary travel shaft applications.
Mechanically flexible U-Joints accommodate end U Joint china movement by utilizing a telescoping shaft (sq . shafting or splines). U-Joints function by a sliding movement between two flanges that will be fork-formed (a yoke) and having a hole (eyesight) radially through the attention that is connected by a cross. They let larger angles than flexible couplings and are used in applications where high misalignment must be accommodated (1 to 30 degrees).
Always make sure fresh, fresh grease is evident in all U-joint seals.
Can be caused by operating angles which are too large.
Can be caused by a bent or perhaps sprung yoke.
Overloading a drive shaft could cause yoke ears to bend. Bearings won’t roll in the bearing cap if the yoke ears aren’t aligned. If the bearings end rolling, they continue to be stationary and can “beat themselves” into the surface area of the cross.
A “frozen” slip assembly won’t allow the travel shaft to lengthen or shorten. Each time the drive shaft tries to shorten, the strain will be transmitted in to the bearings and they’ll tag the cross trunnion. Unlike brinnell marks caused by torque, brinnell marks that are the effect of a frozen slide are often evident on leading and back areas of the cross trunnion.
Improper torque about 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.