What You Need to Know Before Starting

A sliding patio door lock can be replaced without removing the door from its track or calling a locksmith. Most residential sliding doors use one of two lock types: a surface-mounted handle lock (the most common) or a mortise lock built into the door frame itself. You can identify which you have by looking at the inside edge of the sliding door — if you see a small rectangular hole with a bolt, you have a mortise lock; if the lock mechanism sits on top of the door frame, you have a handle lock.

The entire job takes about 30 minutes for a handle lock and up to an hour for a mortise lock. You will need basic tools you likely already own: a screwdriver, a tape measure, and possibly a drill. The lock itself costs between $15 and $60 depending on the type and finish. Buying the exact replacement model for your door makes the job simpler, but a universal sliding door lock will work if you measure the bolt hole spacing correctly.

Key Takeaways

  • Handle locks sit on top of the door frame and are the easiest to replace — you remove two screws and swap in the new lock in under 20 minutes.
  • Mortise locks are built into the door edge and require drilling out the old bolt mechanism, so measure the bolt hole spacing before you buy a replacement.
  • Write down the exact lock model or take a photo before removing the old one, because you may need to order the matching replacement online.
  • Test the new lock with the door open and closed before considering the job complete — the bolt should slide smoothly and catch without binding.

Identify Your Lock Type and Gather the Right Tools

Look at the inside of your sliding door frame where the lock sits. If you see a metal handle with a small lever or button on the frame itself, you have a handle lock — this is the most common type in residential doors built after 1990. If the lock is recessed into the door edge and you see only a small hole where the bolt enters the frame, you have a mortise lock.

For a handle lock, gather a Phillips or flathead screwdriver (check which fits your lock screws), a tape measure, and the replacement lock. For a mortise lock, add a drill with a bit that matches your bolt hole diameter (usually 1 inch) and a chisel if you need to enlarge the bolt pocket. Take a photo of your current lock from the side and front before you start — you will need to know the exact model or at least the bolt hole spacing when you order the replacement.

Remove a Handle Lock in Three Steps

Close the sliding door and locate the two screws on the inside face of the lock handle. These are usually visible on the frame side, though some locks hide them under a small plastic cover that pops off with a flathead screwdriver. Remove both screws completely and set them aside in a small container so you do not lose them.

Slide the old lock handle away from the door frame — it should come free without resistance. If it does not, check that you removed both screws and that no part of the bolt is still engaged in the frame. Once the handle is off, you will see the bolt mechanism and the screw holes where the new lock will attach.

Position the new lock so the bolt aligns with the existing hole in the door frame. Insert the two screws by hand first to make sure they thread correctly, then tighten them with your screwdriver. Do not overtighten — stop when the lock sits flush against the frame. Test the lock by sliding the door open and closed; the bolt should move smoothly and catch without grinding or sticking.

Replace a Mortise Lock: Drilling Out the Old Bolt

A mortise lock requires you to remove the bolt mechanism from inside the door edge. Close the door and look at the small hole where the bolt enters the frame — measure this hole diameter with your tape measure. Most residential mortise locks use a 1-inch bolt hole, but older doors may be different.

Drill out the old bolt using a drill bit that matches the hole diameter. Drill slowly and straight into the door edge to avoid splintering the wood. Once the bolt is drilled through, you can remove the lock handle screws (usually two, on the inside face of the door) and pull the handle away from the frame. The old bolt mechanism should come out with it.

Measure the distance between the bolt hole and the handle screw holes — this spacing must match your replacement lock. If the new lock has different hole spacing, you will need to drill new screw holes and fill the old ones with wooden toothpicks and wood filler. Insert the new lock bolt into the hole first, then align the handle and find it with the two screws. Test the door several times to may support the bolt catches smoothly.

Avoid These Common Mistakes

The most frequent error is buying a replacement lock without measuring the bolt hole spacing. If your new lock's bolt does not align with the existing hole in the frame, you will have to drill a new hole and patch the old one — a job that takes an extra 20 minutes. Take a photo of your old lock or write down the model number before you remove it.

A second mistake is overtightening the screws, which can crack the plastic handle or strip the screw holes. Tighten until the lock sits flush, then stop. If a screw spins without tightening, the hole is stripped — remove the screw, fill the hole with a wooden toothpick and wood glue, let it dry, and drill a new pilot hole slightly offset from the original.

Do not force the bolt if it binds or grinds when you test the door. This usually means the bolt is not aligned with the frame hole or the door is slightly warped. Close the door gently and watch where the bolt enters the frame — it should slide in without resistance. If it catches on one side, loosen the handle screws slightly and shift the lock a fraction of an inch until the bolt moves freely.

Test Your New Lock Before Finishing

Open and close the sliding door at least five times with the new lock installed. The bolt should move smoothly each time and catch with a solid click when the door is closed. Listen for grinding or scraping sounds, which indicate misalignment. If the bolt catches on the frame edge, the lock may need to be shifted slightly — loosen the screws, adjust the position, and retighten.

Check that the door locks and unlocks from both inside and outside. If you have a keyed lock, test it with the key to make sure the cylinder turns smoothly. If the key sticks or requires excessive force, the lock may be installed slightly crooked — remove it, check that the bolt hole is clear of debris, and reinstall it.

When to Call a Professional

If the bolt hole in your door frame is damaged, enlarged, or misaligned, a professional locksmith can drill a new hole and patch the old one cleanly. If your door frame is warped or the door does not close smoothly, the problem may not be the lock itself — a carpenter or door specialist can assess whether the frame needs adjustment before a new lock will work properly.

If you drill out a mortise lock and find that the bolt pocket is too shallow for the new lock's bolt, a locksmith has tools to deepen the pocket without damaging the door. This is a job that takes skill and the right equipment, so it is worth the cost rather than risk splitting the door edge.

Frequently Asked Questions

Can I replace just the lock handle without touching the bolt mechanism?

Yes, if the bolt itself still works. Many handle locks have a removable handle that slides off after you remove two screws, leaving the bolt in place. You can buy a replacement handle that fits the same bolt. Check whether your old lock has a separate handle and bolt or if they are one unit before you order the replacement.

What if the new lock does not fit the old bolt hole?

Measure the bolt hole diameter and the distance from the bolt hole to the handle screw holes on both the old and new locks. If they do not match, you will need to drill a new bolt hole in the frame and fill the old one with wooden toothpicks and wood filler. This adds 20 to 30 minutes to the job but is manageable with a drill and basic tools.

Do I need to remove the door from the track to replace the lock?

No. The lock can be replaced while the door is in the track. You only need to close the door and access the inside face of the lock handle. Removing the door makes the job slightly easier because you can lay it flat, but it is not necessary and adds significant time to the overall project.

How do I know if my lock is broken or just stuck?

Try sliding the bolt back and forth gently with the door open. If it moves freely, the lock is probably just dirty — clean it with a dry cloth and a small amount of silicone spray lubricant. If the bolt is stuck or grinds, or if the key does not turn smoothly in a keyed lock, replacement is the better option than trying to repair it.

What is the difference between a keyed lock and a push-button lock?

A keyed lock requires a key to unlock the door from outside, while a push-button lock (also called a thumb-turn lock) has a button or lever on the inside that you press to unlock. Push-button locks are simpler to replace because they have no cylinder, but keyed locks offer more security. Both types use the same installation process — the difference is only in the handle mechanism.