I'm using a Curt 20k (about 10 years old) so it is a bit aged. Lately while hitching, I was periodically having problems with the jaws completely closing, so I asked my youngest, who is a big rig trucker to check my hitch because I thought it was worn out. After examining the jaws and the mechanism, he told me it was fine but that I needed to keep the king pin positioned more to the right side of the alignment slot rather than the left when backing up to hitch or the jaws will fail to close completely - he also confirmed that I needed to let the trailer slide up the hitch ramp (which I was already doing).
I watched him doing the examination of the hitch and he manually triggered the jaw closing mechanism with his hands to find the ideal spot to position the pin in the hitch head, which is why he told me to hug the right side of the hitch while backing. I've not had a single problem since I followed his advice. His take home lesson was that you sometimes need to manipulate the particular hitch mechanics to determine it's quirks - even though they are mass produced for uniformity, they change their properties as they age.
On an aside, he uses a portable electric grease gun to generously lube the hitch plate every time he hitches his semis, and told me to do the same because he noticed what he called high pressure wear on my hitch head even though I was using a lube plate.
PZ
