My flat's wooden door has an old mortice deadlock that needs replacement. It's one of the old Chubb locks, that apparently (from the info I found online) is now rebranded Union. However, I can only find a few locks online that have similar size (but not 100% identical-which worries me a bit) but are 4-5 times the price of "more modern" models, which seem much more low-profile than the old ones.

These are the pictures and measurements of my old lock:

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And this is a possible replacement:

which however costs much more than other models (which can be found at 20-30 quids), and measurement-wise is slightly taller than my current lock.

Do you have any suggestions on what would be the "best" thing to do, in your opinion?

I'd like to keep the current key hole and don't drill any more holes in the door, but I wouldn't mind to do some chiselling to make room for the slightly larger mortice lock, or use some wood filler and replace the old lock with a smaller one (however, I don't know how easy it would be then to fix the mortice lock on the wood filler with screws.. I suspect it might get a bit messy).

I'm really puzzled and not sure of how to proceed, any suggestion is very welcome :)

  • Please post the images here using the editor rather than linking us out.
    – isherwood
    Commented Jan 31, 2022 at 20:46
  • 2
    I presume the lock is no longer functioning the way it should???? What is nice about these old locks like this is they can be rebuilt by a locksmith. The function on the inside is very simple, they typically last forever. Sometimes it is just a little well placed oil here or there to fix an issue or a cleaning or both.
    – Jack
    Commented Jan 31, 2022 at 20:50
  • @Jack yeah I have a couple of concerns about this lock. The first one is that I just bought this flat (and it was rented before I moved in), so other people might have duplicates of the key. The second one is that sometimes the deadlock gets stuck outside and I get locked out/in the flat, and I need to spend 5 minutes fighting with the key to open the door, with the risk of breaking the key. I am not sure of how simple it would be to solve the problem of the lock getting stuck, and also not sure if it would be possible to change the key that opens it.
    – Fraccalo
    Commented Jan 31, 2022 at 21:26
  • @isherwood sure, will do as soon as I get to my computer, can't easily reduce the size of the pictures from the phone atm.
    – Fraccalo
    Commented Jan 31, 2022 at 21:27

1 Answer 1


There are plenty of "standards" for locations of hole offsets etc. Take your old lock to a hardware store and compare visually

You need to make sure the hey hole is exactly the same position relative to the top/bottom of the lock body. If that doesn't match, you'd have to chisel wood until it is right. A little deeper into the pocket is probably okay - most lock installers go over-deep when cutting the pocket initially.

A replacement may require some subtle chasing of the rebate for the strike-plate face, and the strike-plate might be slightly different too. The screw holes are always in a different place..

Do be aware that the security offered by these locks is relatively low and the old ones tend to have sloppy tolerances due to wear.

Your best option might be to refit this lock in your door, plug the keyhole, and fit a new modern deadbolt in a higher/lower position. Depends if "originality" is important in your view.

  • 1
    I replaced just a door (the old one was severely damaged) a while back. I bought a whole pre-hung unit because it was cheaper than getting just the door slab (go figure). While the hinge mortises all lined up 100%, somehow the door knob for the new door didn't quite line up with the old latch mortise. I chiseled out a rectangular section in the door frame, glued in a new piece of wood, then drilled out a new mortise for the latch. When I reinstalled the strike plate, I used very long screws to ensure they went into the framing. This is doable!
    – FreeMan
    Commented Feb 1, 2022 at 17:38
  • @Criggie thanks for your answer! Do you have any links to modern deadbolts that you would consider "more secure"? Anything specific I should for? Even a picture would help, just to understand what type of lock you mean :)
    – Fraccalo
    Commented Feb 1, 2022 at 18:22
  • 1
    @Fraccalo probably better to talk with a local locksmith on that side. A deadbolt would be something like prod-trudoor-media.s3.us-west-2.amazonaws.com/wp-content/…
    – Criggie
    Commented Feb 1, 2022 at 21:42

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