Looking for (experienced?) advice on my antique mortise lock.

I bought a door with an included mortise lock in SC. The bolt bears the name "Clinton," which I believe to be a late 1800s lock company from Seneca, SC (been a few years since I did this research)

I cleaned and graphited the lock about 3 years ago, and it's remained in a fair operating state since then. Here's how it functions: Interior - round knob. Kind of binds after opening, doesn't like to return to 0 degrees. (I haven't installed the interior face plate yet, so some of the binding may be as a result of that.) Exterior - lock functions as expected, key will open bolt and latch in a pinch. Handle is lever-type (push down on the lever with your thumb, latch releases) and works exceptionally poorly, except when it wants to.

It hasn't taken much work to determine that all the issues are related - when the handle is turned, the outside lever can't be operated and vice-versa. I had the lockset out for other maintenance and decided to crack it open and investigate why the functions were not playing nice.

At the top of this image, you can see where the two mechanisms interact. A photo of the inside of a mortise lock with the cover removed

And in this image you can see the three components of the two mechanisms. Three levers from the inside of a mortise lock

The round piece with the square hole turns as the interior handle turns. It will push the L-shaped lever towards the bottom of the photo whether turned clockwise or counter-clockwise. The funny-shaped piece that has an E-shape in the middle is raised by the lever. As it moves up, it pushes the bottom of the L-shaped piece up, forcing the long end towards the bottom of the photo as it pivots on the fulcrum at the joint of the L.

These parts are all in working order as far as I can tell, so my questions are:

  1. What is the design function of the raised nubs on the "E"? I can tell they are supposed to mesh with the piece sticking out of the round piece, but it's unclear what purpose "don't let the handle and lever be used at the same time" serves.
  2. Depending on the answer to 1, would removing the center or both nubs on the E, or shaving them down so they're at a steeper angle rather than rounded, be a bad idea? I don't like the idea of defacing antiquities, but if it takes the door from "almost broken" to "works fine," I'm willing to try just about anything.
  3. I spent a lot of time trying to find an appropriate forum to ask this question in. There's only one site I came across that seems relevant, but it seems to be focused on antique padlocks, rather than mortise locks. If there is a better forum to ask this, or if a referral to a locksmith with experience in mortise locks is required, I'm open to suggestions.

Thanks all in advance.


Edits: 1a: I had forgotten how the day/night function works and overlooked that while puzzling about why the E-shaped piece doesn't do what I want. 1b: This came with a round knob. I tried using a small brass "handle" that rests parallel to the ground, but the spring was not strong enough to bring it back to level and the exterior latch stayed bound up with that handle installed. Only by the grace of a mail slot was I able to get back in the house without the keys. 1c: This door was not painted when I bought it, and as a result, the mortise was unpainted. The mortise was bent slightly and not lustrous, so I took the time to sand and brass wool it into shine, clear-coated the face without any parts inside, then sanded any overspray off the bolt and latch holes.


1 Answer 1


Beautiful. The function of the E-shaped piece is related to the toggle buttons and their mechanism on the top right of the photo. They control the function of the exterior knob.

With one button pressed, the exterior knob cannot turn and the latch must be opened with the key or with the interior knob. With the other button pressed, the door can be opened from outside unless it has been deadlocked with the key. The E-shaped piece is part of that mechanism. The chunky square block attached to it is how the exterior knob operates the latch, unless disabled. Here's a video showing how. You should watch the whole 4-part series.

Re binding:

  • Replace the latch coil spring. It doesn't look in great condition. Maybe also the spring hidden behind the "L" shaped piece, you can see a bit of it at the top left of the main photo. The coil spring can be easily sourced if you know its specs (which you of course do not). The other one probably needs to come from or be made by a locksmith.
  • Remove paint from the latch and its faceplate.
  • Do a better job at removing rust and preventing rust from the moving parts.
  • 2
    You may also want to apply a light coating of lithium grease to the moving parts. In modern locks you need to be very careful to use only dry lubricants and to use those sparingly;.these larger (and less finely machined) parts are both more tolerant and in greater need of lube.
    – keshlam
    Commented May 27 at 13:15
  • @keshlam OP said is using graphite lube. Idk if that's better here than lithium but it's not bad.
    – jay613
    Commented May 27 at 13:54
  • 1
    In this case I would actually go with a touch of light grease, due to the scale we're working on. But graphite, used sparingly, is certainly not going to do any harm.
    – keshlam
    Commented May 27 at 14:00
  • @jay613 - well noted. When I took the lock apart a few years ago I learned how the day/night lock setting works and was satisfied with that. Armed with that information, I took apart the lock yesterday and confidently forgot that there are two different functions on the same armature. As for springs - I believe the spring behind the L-shaped pieces you're referring to is actually part and parcel with the L--shaped piece (see second photo.) Can you confirm if that's the case? I'll take your word for it being in poor shape - can you expound on what makes you feel as though it is?
    – Steve
    Commented May 27 at 14:29
  • Yes, The spring attached to the L-shaped piece appears to be wedged into a slit. I can't tell if that one is good or bad, but there's a high chance your problem is caused by its age. It is the other one, the coil spring on the latch, that may also contribute to your problem and that looks bad to me because the windings are uneven especially in the middle. That's often a sign of age.
    – jay613
    Commented May 27 at 15:33

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