Cleaning and Repairing an Antique Mortise Door Lock




Introduction: Cleaning and Repairing an Antique Mortise Door Lock

If you have an older house with knobs that slip, latches that are stuck inside the door, or other minor problems, then you should follow these instructions to remove the lock, dis-assemble it, clean and perform minor repairs.

Step 1: Meet the Mortise Lock and Door Knobs.

This mortise lock set is installed in a 1930 colonial in the Boston area.

Notice the set screw on the base of the knob on the right. This screw should hold the knob securely to the spindle when you turn the knob.

Step 2: What's a Spindle?

The spindle is threaded to hold the knobs on, but has flats to operate the lock mechanism and to allow the set screws in the knob to hold the knob securely to the spindle.

If the set screws become lose they will allow the knob to turn without actuating the lock mechanism. If your knob is "slipping" try tightening this screw.

Prolonged use with a lose set screw can damage the spindle. If tightening the set screw does not help, you should be able to buy a new spindle at your local hardware store (not the chain with the 16 year old clerk, find the one with the proprietor who is approximately as old as your home).

Step 3: Loosen the Set Screw.

To remove a knob, find the set screw on the base and loosen it just enough that the handle turns freely on the spindle.

Step 4: Remove a Knob From the Spindle.

Unscrew that knob from the spindle. Make sure not to drop it!

Step 5: Remove the Spindle From the Door.

To remove the spindle, pull on the other knob with the spindle attached.

If you need to replace the spindle loosen the set screw on this knob, and unscrew the spindle from the knob to remove it.

Reverse your steps from this point to install the new spindle.

Step 6: Free the Lock Face From Any Paint.

Before you remove the lock mechanism from the door, you may want to score the gap around the lock front with a razor to free any paint that may be attached to the metal.

If there is paint on the lock face, then when you remove the mechanism the paint may stick to the lock face and peal off the wood of the door.

Step 7: Remove the Lock Face Screws.

To free the lock mechanism from the door, remove the two screws in the lock face.

Step 8: Pop the Lock Case Out of the Door.

To extract the lock mechanism from a tight mortise hole, place a small screw driver through the hole where the spindle was and gently push forward to free the lock face from the wood.

Step 9: Remove the Lock Case From the Door.

The lock mechanism should come freely out of the door.

Step 10: Open the Lock Case.

Beware that several components inside the case may be attached to springs. If you are not careful when you open the case, you will not get a chance to see how the inner workings are supposed to fit together, or worse parts, may fly off into the far corners of your workspace.

Carefully remove the screw while holding the case together.

Step 11: Freeing the Latch

If you need to reverse the latch so that it closes the other way, gently remove the latch while holding the other parts in place, and re-insert it with the angled end facing the other direction.

If that's all you needed to do, reverse your steps from this point to re-install the lock.

However, look at all those cobwebs! Lets continue on to clean the lock.

Now would be a great time to take a photo of your lock mechanism so you can put it back together later.

Step 12: Disassemble the Latch Mechanism

The latch/knob mechanism should not have particularly powerful springs, just be careful not to lose any of the pieces.

Step 13: Disassemble the Dead Bolt Mechanism.

The deadbolt mechanism will have a powerful spring. Press the gate toward the top of the lock mechanism, lift it over the top of the cam on the deadbolt , and gently release the spring tension until you can safely lift the gate off it's pin.

Step 14: Keep Track of the Parts!

I warned you about losing parts, right?

Step 15: Secure the Lock Case.

The main lock body should be cast and fairly durable. The lock face is likely brass and is therefore easy to dent and even bend. Use a vise to hold the case body so you can clean the face, but do not over-tighten the vise or clamp directly to the brass face, or you will damage your lock.

Step 16: Polish the Brass Lock Face.

Use 0000 steel wool to polish the lock face. Do not think you are clever and use sand paper to rush the job along. Be patient. Remember you are here because some lazy sod didn't bother ot remove the lock before painting. Look at all the gunk on there! Do not repeat their mistake. Patience!

Step 17: Decide What to Do About Dings and Dents.

You may reveal marks from the craftsman who built your lock. All mine have unique numbers stamped into the faces.

Deep dents or gouges in the brass will resist polishing. You can decide to try to clean them out but I just leave them dark. They add character.

Step 18: Polish the Exterior Latch and Dead Bolt Surfaces.

The latch and possibly even the deadbolt will also be polished brass. You can clean them with steel wool in the same way you cleaned the lock face. I don't put them in the vise to polish, I just hold them in my hand.

Step 19: Clean the Case and Parts With WD-40.

If you did it right, your lock case will be full of steel wool dust. Clean it and all the other parts with a paper towel and WD-40.

Do not use oil!

Get all the dust, cobwebs, and steel wool out of the case and off the parts.

Step 20: Re-install the Deadbolt and Prepare the Gate.

The first tricky part of re-assembly is to get that gate back on with that stiff leaf spring. With the deadbolt in place, reverse your steps: gate on pin, leaf spring against the stop, gently squeeze the gate into position...

Step 21: Attach the Gate to the Dead Bolt.

...and drop it onto the cam of the deadbolt. Tension should keep it in place.

Step 22: Replace the Latch Spring.

If your latch spring is broken or weak then you'll need a replacement.

You can take the lock to a local locksmith (find the one that's been around since your house was built).

If you have a good spring (maybe in a different lock) you can measure the length of the spring when un-tensioned. Then hang weights from it to determine the amount of force needed to start stretching it (the spring pretension force) and then amount of additional force needed to stretch it a specific distance (the stiffness of the spring) then you can go find one online.  The McMaster-Carr site has a great search engine for springs.

My locks took this spring:

Step 23: Prepare the Latch Mechanism.

The latch mechanism can be tricky since the top of the case normally holds it in place. I put the parts together as much as possible with the spring un-tensioned.

Step 24: Tension the Latch Spring.

I use a screw driver to tension the latch spring and hold everything into place.

Step 25: Use the Screw Driver to Hold Everything in Place.

Notice that the case top is already on the screw driver so I can drop it into place.

Step 26: Close the Case Top.

Once the case is closed, the latch mechanism should stay in place while you tighten the case screw.

Step 27: Test the Mechanism on the Bench Before Re-installing.

Do not over-tighten the case screw or it will bind the mechanism. Test by using a screw driver to actuate the mechanism. If the latch doesn't come back out when you release the screw driver, then you've either over-tightened the screw, or something else is out of place inside.

If you have a key for the lock, also test the deadbolt.

Now is your chance to fix things, if you don't test it until you have it back in the door, you'll be sorry when you have to tear it all back out and bring it back to the bench.

Make sure your latch is the right way too, if it's backward fix it now.

Once you're satisfied, reverse your steps to re-install the lock set in the door. If the case doesn't easily slide in to the door, use a rubber mallet to gently tap it into place. Do not use a metal hammer or you will mar the surface of the lock face. If you do not have a mallet use the plastic handle of your screw driver.

Step 28: Note That There Are Many Kinds of Locks.

Note that not all mortise locks are the same inside. I have two kinds of lock mechanisms that look almost identical from the outside but have a slightly shorter face and a slightly shallower backset.

The latch mechanism on this lock is easier to work with because it doesn't fly apart when you open the case.  There's a leaf spring for the knob return and a separate coil spring for the latch return. Also the the spindle cam pushes directly on a combined arm/transit.

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    75 Discussions


    Question 1 year ago

    I just need to know where to put all 3 springs (Or pins, More like tiny leaf springs actually) and only found one videi for this exact model. Please help?


    Answer 18 days ago

    Where can I get parts


    Question 1 year ago on Step 28

    do you have any experience with old pocket door "pulls". There are little thin metal strips that seem to be required. I think I have all the pieces, but I am not sure where they go as I have yet to find a picture of the insides of a "working" pull. It's one where you press a button and the "pull" snaps out.


    1 year ago

    I've spent many lovely hours cleaning and restoring the antique door locks on our 1880's Melbourne Australia villa house. The workmanship in this old locks is delightful. You can really understand the term "locksmith" which I think is a misnomer for many of the current tradespeople. Some of the workings in two of our locks were broken but I was able to pillage from one to make up one whole functioning lock. I then spent months of weekends scratching around in junk and building salvage yards looking for a matching lock and eventually found a couple inside some antique doors. I managed to convince the owner to remove and sell the locks for me and voila. Two fully functioning locks and a spare for future repair. I just hope the universe will forgive my lifting locks that had been in existing doors. cheers


    Tip 1 year ago

    Don't use steel wool on brass as the steel will embed itself into the brass and cause corrosion. Use brass wool instead.


    Reply 1 year ago

    that's great advice, I didn't know brass wool was even a thing. That makes a lot of sense.


    Question 2 years ago on Step 28

    Where can I get the correct compression spring for this type of lock?


    Question 2 years ago on Step 27

    Is there way to find the key for these particular locks? I don’t know what to look for.


    8 years ago on Step 28

    WARNING! If it's a lock for an OUTER door, the spindle will be in 2 pieces. When you push the button on the lock face the OUTER knob is supposed to lock. If you screw the spindle halves together tightly (rather than leaving 1/2 turn of slop or more) BOTH sides of the door will be locked! Also, the split in the spindle is supposed to be in the vertical center of the lock-pay attention when installing and TRY THE LOCK WITH THE DOOR OPEN.

    The usual reason mortise locks stop working is broken springs-one would do well to replace them all, if possible. A good way to clean out the lock body is with brake cleaner spray, followed by wiping with a paper towel. One of the FEW things graphite is good for is lubing the inside of a mortise lock body-if it has a cylinder for a key, lube with WD40 (or similar light spray oil) ONLY-no 3-in-1, no grease, no silicone spray.

    Frequently the bolt will be bent from attempts to close the door with it extended. Being brass, they can be CAREFULLY straightened.

    Painted hardware can be cleaned with paint remover and/or with a Dremel and rotating brush. The brass can polish up like new, but will have to be varnished or waxed after. NOTE: Some finished were purposely antiqued and won't like that way after polishing!


    Reply 2 years ago

    Thanks for this bit of info. I had no idea to leave the 1/2 turn of 'slop'. Makes all the difference.


    Reply 8 years ago on Introduction

    Sorry, but NEVER use WD-40 in a lock. It is a penetrant, but will dry out and gum up rather quickly, attracting abrasive dust.
    Use dry graphite only, use a Q-tip or puff applicator to apply.

    NEVER use varnish if you can avoid it. It does not hold up as well as CLEAR LACQUER IMNSHO.

    Large towns' locksmiths will (or should) have the correct key blanks to make up a proper set for the door(s). They will need to be cut to fit correctly! Many skeleton keys will NOT work, especially for entrance doors. Even the sellers of mortise locksets say that skeleton keys will fit MAYBE 30% of doors...and that does not mean they will work, just that they will fit.

    One more thing: interior lock springs were of three types; flat springs, compression springs (often used on the strikes), and tension springs (used on the bolts, etc.). You CAN find close approximations at some GOOD hardware stores, auto supply stores, and GOOD locksmiths.
    You will likely NOT find flat springs at most places. Locksmiths are your best bet, especially the older shops.

    And why do springs fail? Because the lock dried out the lube or wore it away, and folks force the lock to work when it should be EASY...this is why other lock parts get broken as well.

    Hope this helps.


    Reply 4 years ago


    I came across an old Peterboro key lock for an interior(?) door. It had been taken apart and partially cleaned. I cleaned the rest, but now I need help putting it together again. I looks like all the parts are there. It has glass knobs and I have bought new stems/rods for them, because the old ones were worn.

    Could I send you pictures so you can identify the lock and hopefully give me instructions on how to pput it together. Of course I would be willing to compensate you.


    Reply 4 years ago

    Would you have a similar lock in the house? Carefully removed and used as an example, it might serve.
    I would recommend just trying different assemblies, keeping track of how you put any particular part together...dead bolt assembly, for example.
    I had recently tried a piece of steel from a clock spring (wound type) as a replacement for the flat springs in a few locks. While not stiff enough by itself, a couple/three together might serve.
    I'm the type that needs a bunch of pieces in front of me to work, so sending me pics would probably not help.


    Reply 8 years ago on Introduction

    Sorry to contradict. I have been a locksmith for more than 30 years. Much of that experience was rebuilding/repairing older residential mortise lock, some older than 100 years.

    I have used WD40 for all of that time with great success in commercial, residential and auto locks, Example: I owned a car for 17 years. In that time I lubed the locks every 3 months with WD40 and they never froze or failed. Yes, it's a penetrant-with lubricating qualities. PBlaster, on the other hand has no lubing effect, and will cause locks to work HARDER immediately.

    Graphite use hails from the time when locks only had large sliding parts with lots of tolerance. It still works fine with mortise lock bodies, but not in pin tumbler cylinders. I have seen cylinders so full of graphite they didn't move. WD40, on the other hand, will dissolve old oil and I have seen it immediately loosen up recalcitrant locks. I recommend it because it's easy to find and hard to overuse (it should not be used with most plastics-they may melt).

    Varnish is OK as long as it's polyurethane-some lock makers use it as a finish.

    "Skeleton keys" come in three patterns, one of which will open nearly all INTERIOR locks. EXTERIOR locks work on BIT keys, which must be cut by a locksmith (they have more complicated combinations since they contain more lever tumblers).

    The majority of spring breakage I have seen was the result of rust or loss of temper of the steel.


    Reply 4 years ago

    You are even more than awesome because I was able to take the handles apart and get a screwdriver to turn just the one side!


    Reply 4 years ago

    Very glad I could help!


    Reply 4 years ago

    You are awesome! I just bought a house and my inside handle would lock when I locked the front handle and I had no clue why. Unfortunately, now both handles are locked and I cannot get the key to work on the outside. :-( I'm stuck and I have no idea how to get this door open.