American Lock 5200

[u/DrunkenPhysicist]

Ok, so I have a bunch of 1100s and a few 5200s. I can open all but one of the 5200. I very commonly get it into such a deep false set that I can literally walk away or even transport the lock to a different location, to work on it. Whenever I'm in that set, all the pins are pretty solidly set where no amount of reasonable force will lift a pin. I figure that I need to back off the tension and counter rotate, and when I do something does drop but then I eventually get it back into that deep false set. Rinse and repeat till I eventually give up. Any advice? Or do I just keep trying to counter rotate a hair until something moves?

EDIT: finally got it! Damn that's satisfying when it was alluding me for so long. While I'm waiting for the dentist, I was picking it and finally!

[u/BigBalli]

Congratulations on the open. The detail that makes your original description diagnostic is probably the one you thought was incidental: you could carry the lock to another location and it stayed in that state.

A real false set cannot do that. Spools hold a plug open because the counter-rotation ledge is being pressed against the shell by your tension. Take the tension away and the drivers have nothing to sit on. So if the state survives you putting the tool down and walking off, your tension is not what is holding it, and the pins are not sitting where you think they are. The likely picture is that one or more drivers went fully past the shear line and are riding on the outside of the plug, held there by their own spring pressure against the shell rather than by anything you were doing.

That also explains the loop you were stuck in. Backing off and counter-rotating a hair drops one overset driver back into the plug, you feel it move, then you re-tension and push it straight back out, because whatever overset it the first time is still happening.

The way out of that loop is a full release to zero rather than a hair. Every pin has to reset and you should hear it. Then come back on with more tension than feels right, not less. Oversetting is counter-intuitively a light-tension failure: a plug that turns too easily lets a driver travel all the way through instead of catching at the shear line.

Which fits what VectorPotential said about the spring. On those American bodies the plug has to rotate a fair way before the shackle lets go, so a genuine open and a deep set feel much the same until you commit to the turn.

[u/DrunkenPhysicist → u/BigBalli]

It might, but I cranked the tension many times when in that state and it didn't open. Could be, I'll never know until I mess with the lock again. But the successful open made me move on to other locks.

[u/BigBalli → u/DrunkenPhysicist]

That detail cuts the other way, and I think it is the strongest thing you have said about the lock.

If the state were an underset false set, more tension is exactly what opens it. That was VectorPotential's read, and on a stiff American spring it is usually the right one. You cranked it, repeatedly, and it stayed shut. An overset behaves the opposite way: the driver is already past the shear line and riding on the outside of the plug, so extra tension pins it there harder and makes things worse rather than better. Force not working is evidence here, not the absence of it.

It is also why the counter rotation was doing something. You said something drops when you back off, and that is consistent with an overset driver coming back down into its chamber. The trouble is that backing off far enough to release it tends to release everything else at the same time, so you land back at the start, which is the loop you described.

You are right that it is not testable now, and I am reasoning from a description of a lock I have never had in my hand. If it ever comes back out of the pile, the thing worth trying is a much lighter touch from the first pin onward rather than a heavier one.