U Joint

There are many varieties of U-Joints, a few of which are very complex. The simplest category known as Cardan U-Joints, are either block-and-pin or bearing-and-cross types.

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

Using the wrong lube can bring about burned trunnions.
Unless usually recommended, use a high quality E.P. (extreme pressure) grease to support most vehicular, U Joint professional and auxiliary travel shaft applications.
Mechanically flexible U-Joints accommodate end movement by using a telescoping shaft (sq . shafting or splines). U-Joints function by a sliding motion between two flanges that will be fork-formed (a yoke) and having a hole (vision) radially through the attention that is connected by a cross. They allow larger angles than flexible couplings and are used in applications where excessive misalignment should be accommodated (1 to 30 degrees).

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

Can be due to operating angles which are too large.
Can be caused by a bent or sprung yoke.
Overloading a travel 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 stay stationary and will “beat themselves” in to the surface of the cross.
A “frozen” slip assembly will not allow the drive shaft to lengthen or shorten. Each time the travel shaft attempts to shorten, the strain will be transmitted into the bearings and they will mark the cross trunnion. Unlike brinnell marks due to torque, brinnell marks that will be the effect of a frozen slip are often evident on leading and back floors of the cross trunnion.
Improper torque on U-bolt nuts could cause brinelling.
Most makers publish the recommended torque for a U-bolt nut.
Improper lube procedures, where recommended purging isn’t accomplished, can cause one or more bearings to be starved for grease.


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