U Joint

There are many types of U-Joints, a few of which are very complex. The simplest 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 models solid and bored. Solid hubs do not have a machined hole. Bored hubs possess a hole and so are called for the hole form; round, hex, or sq . style. Two bored models that deviate from these prevalent shapes are splined, that have longitudinal grooves inside 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 normally recommended, use a superior quality E.P. (excessive pressure) grease to support most vehicular, industrial and auxiliary drive shaft applications.
Mechanically flexible U-Joints accommodate end movement by simply utilizing a telescoping shaft (square shafting or splines). U-Joints function by a sliding movement between two flanges that are fork-shaped (a yoke) and having a hole (attention) radially through the attention that is linked by a cross. They allow larger angles than flexible couplings and are used in applications where high misalignment needs to be accommodated (1 to 30 degrees).

Always make sure new, fresh grease is evident at all 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 aren’t 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 won’t allow the drive shaft to lengthen or shorten. Each and every time the travel shaft attempts to shorten, the strain will be transmitted in to the bearings and they’ll mark the cross trunnion. Unlike brinnell marks due to torque, brinnell marks that are caused by a frozen slide are often evident on the front and back floors of the cross trunnion.
Improper torque about U Joint U-bolt nuts could cause brinelling.
Most manufacturers 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.