How to Remove and Repair a Mortise Door Lock: A Step-by-Step Guide

Updated at: 27/03/2025

Mortise locks, with their elegant profile and robust security, are a hallmark of quality doors. However, these intricate mechanisms can sometimes malfunction, requiring repair or even replacement. Whether you're facing a sticky latch, a broken key, or a completely jammed lock, tackling the issue yourself can save you significant expense and frustration. Understanding the inner workings of a mortise lock isn't as daunting as it might seem; with the right tools and a methodical approach, you can restore your door's security and functionality.

This guide provides a comprehensive, step-by-step process for removing and repairing a mortise door lock, empowering you to handle the job efficiently and confidently. From identifying the correct tools and understanding the lock's components to reassembling and testing your repair, we'll guide you through each crucial stage. Let's begin by exploring the essential steps involved in this rewarding DIY project.

Preparation and Safety Guidelines

Tools Needed
  • Screwdriver (Phillips and flathead)
  • Possibly a set screw driver
Safety Guidelines
  • Always disconnect the power to the door circuit breaker before starting any electrical work. This prevents electric shock.
  • Take photos or detailed notes of each step as you disassemble the lock. This will be invaluable during reassembly.
  • Use the correct tools for the job to avoid damaging the door or lock mechanism. Improper tools can cause irreversible damage.

Step-by-Step Instructions

  1. Remove Door Handle

    • Remove the door handle by loosening the set screw and unscrewing the handle.
    • Remove the threaded rods holding the handle in place.
    Remove the threaded rods holding the handle in place.Remove the threaded rods holding the handle in place.
    Remove Door Handle

  2. Remove Trim Plate

    • Remove the trim plate by unscrewing the screws.
    Remove the trim plate by unscrewing the screws.
    Remove Trim Plate

  3. Remove Key Cylinder

    • Remove the key cylinder by loosening the set screw and unscrewing the cylinder.
    Remove the key cylinder by loosening the set screw and unscrewing the cylinder.
    Remove Key Cylinder

  4. Remove Lock Case

    • Remove the lock case by unscrewing a couple of screws. If you have a thumb trigger, lift it out of the way first.
    Remove the lock case by unscrewing a couple of screws. If you have a thumb trigger, lift it out of the way first.
    Remove Lock Case

  5. Open Lock Case

    • Open the lock case by unscrewing two screws on the side.
    • Remove the side plate to access the internal mechanisms.
    Remove the side plate to access the internal mechanisms.Remove the side plate to access the internal mechanisms.
    Open Lock Case

  6. Reassemble

    • Reassemble in reverse order, making sure the key cylinder is properly aligned and the set screw is tightened.
    Reassemble in reverse order, making sure the key cylinder is properly aligned and the set screw is tightened.
    Reassemble

Read more: 3M Thinsulate Window Film Installation: A Step-by-Step Guide

Tips

  • If your door handles are on both sides of the door, remove both before proceeding.
  • Mortise locks vary; your internal components may look slightly different.
  • Adjust the lock cylinder's set screw to ensure proper operation and alignment with the door. The cylinder can extend further than expected.
  • To solve a latch bolt that locks in both directions, reverse the hub ring.
  • Understand the function of the stop and release plungers in relation to the thumb trigger mechanism.

Common Mistakes to Avoid

1. Striking Plate Misalignment

Reason: The latch bolt doesn't align correctly with the strike plate, preventing the door from closing or latching properly.
Solution: Adjust the strike plate screws or reposition the strike plate to perfectly align with the latch bolt.

2. Incorrect Latch Bolt Depth

Reason: The latch bolt is either too short or too long, resulting in poor door closure or difficulty locking/unlocking.
Solution: Use shims to adjust the latch bolt depth or replace the latch bolt with one of the correct length.

FAQs

What tools do I need to remove and repair a mortise lock?
You'll need a screwdriver (likely both Phillips and flathead), a chisel, a hammer, a punch, possibly a lock pick set (depending on the repair), and a pencil for marking. It's also helpful to have a replacement lock mechanism on hand.
Can I repair a broken mortise lock latch or just replace it?
Depending on the damage, you might be able to repair a broken latch by replacing individual parts. However, if the damage is extensive or the lock is very old, replacing the entire mechanism is often simpler and more reliable.
How do I avoid damaging the door during the removal and repair process?
Work slowly and carefully. Use the right size chisel and hammer to avoid splitting the wood. Protect the surrounding door frame and jamb with masking tape. Marking the screw and latch positions before removing the lock can greatly aid in reinstallation.