Brand new Trek T900 w/Grip Shifters. The right-hand unit split apart in the 2nd week and the twist grip will not lock into the stationary part anymore. It shifts fine, sort of, if I remember to apply inward pressure as I am rotating the grip. Solution:triggers. Recently bought a ~20y.o. Burley Samba Tandem w/Grip Shifters. Really, really leery about them even though they look and feel solid and are obviously way better constructed than newer ones. They are there for now but I am on the lookout for some triggers to replace them with, my knee jerk reaction to anything head scratching concerning a Grip Shifter(s) is replace with triggers ASAP!