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

1. Speed – Block and Pin or Friction bearings as they are also called can only run at a maximum of 1750 rpm. This limiting speed is due to the fact the design of the block can seize if ran too fast and the heat generated by the joints speed causes the block to expand and cause the pins to seize in their holes.
2. Angle of misalignment – This again is another limiting factor of the block and pin 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 pins in the block lubricated.

Regardless of how slow its run, the angle of use and even constantly greased (huge maintenance overhead) the pins will still wear in the block, leading to increased vibration meaning the block and pin 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 block and pin.

Twin Spring Coupling is an alternative to block and pin/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.