Friction bearing or Block and Pin universal joints are a cheap coupling but with their own disadvantages.

1. Speed – Friction bearings can only run at a maximum of 1750 rpm. This limiting speed is due to the block seizing if ran too fast and the heat generated by the joints speed causes the pins to seize in their holes.
2. Angle of misalignment – This is another limiting factor of the friction bearing uni joints. It is limited to 25 degrees because the design of the pins in the block this is as much as it can flex.
3. Constant greasing – The design of the u-joint means that being constantly fed grease is the only way to keep it from seizing from the angle of use as well as the speed. The grease builds a layer of protection and keeps the bearing lubricated.

Regardless of how slow its run, the angle of use and even constantly greased (huge maintenance overhead) the pins will still wear the block, leading to increased vibration meaning the bearing cross have to be replaced. usually at a cost of 50% of the original purchase price.

This makes these cheap uni joints not so cheap , both with the constant greasing and inspection, as well as the eventual replacement of the bearing cross.

Twin Spring Coupling is an alternative to friction bearing uni joints with none of the downside

TSC can

Run up to 7000 rpm

Flexible to us to 45 degrees

No internal components that need constant greasing and replacing.