Since our business is laser shaft alignment, aka coupling alignment, we address many types of coupling failures.  By far the most common failure is due to lack of lubrication(grease).

The Falk grid type, or the Amerigear gear type couplings, cannot operate very long without grease.  Without lubrication, the steel components in the coupling wear out.  As they wear, the overall vibration levels increase.  As the vibrations increase, the life of the bearings and seals decrease. 

A WWTP had reported high vibration levels on one of their Hoffman air blowers. It sounded like it was coming from the drive end of the blower. Vibration analysis confirmed the drive end bearing was indeed worn, but both motor bearings were also showing some wear.  Further investigation revealed the Amerigear coupling had never been lubricated during 15 years of operation.  The operator didn't know he was supposed to lubricate the coupling!  We replaced all of the bearings in the drive train, and installed a maintenance free Lovejoy type coupling.  This unit should be fine for another 10 years, or more.

Another industrial customer contacted me to do a laser shaft alignment of one of their large 400 HP fans.  Apparently the gear type spacer coupling had been operating without grease for many years when the coupling hub finally broke in half!  Before it failed, the increased vibration put so much stress on the drive end fan pillow block bearing that it also suffered a severe failure. Further investigation also revealed the opposite drive end PB bearing was very worn, and loose on its' mounting.

It is unfortunate that most of these couplings do not have grease fittings.  They are designed to have the plug removed and the fitting installed each time grease is added.  I suspect this is the reason many technicians do not bother to lubricate the couplings-too much trouble.  However, as you can see, the consequences of not adding grease can be very costly! 

Invest in PM, it will save you money!