so I'm trying to replace an old double keyed deadbolt with a kwikset latched deadbolt in a very old front door. The "knob" holes for the deadbolt are a perfectly fine size, but the hole cut for the bracket (not the strike plate, but the bracket that holds the deadbolt against the edge of the door itself) is cut way too large for the new one, and the mounting plate can't fit. I was gonna embrace the improvisational spirit and reuse the bracket plate from the old deadbolt, but I'd have to file the opening open and don't have a file set, and don't know if they would fit compatibly even if I did. The old deadbolt is probably really old, so it's way bulkier than the new kwikset one that I got at the hardware store and I'm worried it won't fit properly regardless. I can't replace the door or do anything too crazy since I'm a renter and it's a 100-ish year old house (but this small project is cleared, just gotta be a bit restrained.)

I've attached a rough diagram to try to make the issue a bit clearer. The red rectangle indicates where the new deadbolt assembly falls within the preexisting hole in the door for the current deadbolt. Is there a good way to make this work, or am I stuck with my current setup?

Drawing of isometric view of a door, with new mounting plate dimensions highlighted in red, showing that the current hole for a deadbolt assembly  is too large.

1 Answer 1


Generally you take a piece of filler wood cut to the dimension of the old mortise lock, screw it into the door from both front and back face and then fill in the remainder with bondo. Once the bondo has set you re-drill the holes using a lock installation tool. I like the dewalt D180004 as this aligns all the holes in 3d space.

dewalt lock install kit

  • I’m not sure we’re dealing with an old mortise lock here. OP, can you add some actual pictures to show what’s going on? Commented Mar 6 at 14:48

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