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

U-joints can be found with two hub types solid and bored. Sturdy hubs don’t have a machined hole. Bored hubs possess a hole and are named for the hole form; round, hex, or square style. Two bored types that deviate from these prevalent shapes are splined, that have longitudinal grooves inside bore; and keyed, that have keyways to prevent rotation of the U-joint on the matching shaft.

Using the incorrect lube can bring about burned trunnions.
Unless in any other case recommended, use a high quality E.P. (severe pressure) grease to services most vehicular, professional and auxiliary travel shaft applications.
Mechanically flexible U-Joints accommodate end movement by U Joint china simply by using a telescoping shaft (square shafting or splines). U-Joints function by a sliding movement between two flanges that will be fork-shaped (a yoke) and having a hole (eyesight) radially through the attention that is connected by a cross. They let larger angles than adaptable couplings and are used in applications where large misalignment has to be accommodated (1 to 30 degrees).

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

Can be caused by operating angles which are too large.
Can be the effect of 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” in to the surface area of the cross.
A “frozen” slip assembly will not allow the travel shaft to lengthen or shorten. Every time the drive shaft attempts to shorten, the load will be transmitted in to the bearings and they will tag the cross trunnion. Unlike brinnell marks due to torque, brinnell marks that will be the effect of a frozen slip are generally evident on leading and back surfaces of the cross trunnion.
Improper torque about U-bolt nuts can cause brinelling.
Most producers 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.