Window Lock Replacement: Match, Remove and Install Sash Locks

A broken sash lock rarely looks urgent until you realize the window cannot be secured, or it rattles every time the wind blows. The good news is that window lock replacement is usually a 15-minute job with a screwdriver, provided you buy the right part. Most failures come not from the installation but from ordering a lock with the wrong screw-hole spacing, the wrong hand or the wrong height.

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The short answer: remove one old lock, measure the center-to-center distance between its screw holes and the height from the sash to the underside of the cam, note whether it is a cam, lever or tilt-latch design, and photograph it next to a ruler. Buy a replacement with the same hole spacing and style, screw it into the existing holes, and adjust the keeper so the lock pulls the sashes tight. If you want to change window locks for better security or looks, stick with the same footprint to avoid drilling new holes in vinyl or aluminum frames.

This guide covers identifying the type, measuring and sourcing a match, step-by-step removal and installation for double-hung, slider and casement windows, and fixing keepers that refuse to line up.

Window Lock Replacement: Identify Your Lock Type

Before any window lock replacement, figure out what you have. The window style narrows it down quickly:

• Cam (sash) locks on double-hung and single-hung windows: a rotating curved cam mounts on the top rail of the lower sash and hooks into a keeper on the bottom rail of the upper sash. By far the most common type.
• Tilt latches: spring-loaded slides on the top corners of tilt-in sashes. They hold the sash in the frame and release it for cleaning. They are not the main lock, but they often break and are replaced the same way.
• Slider latches: on horizontal sliding windows, a latch on the meeting rail of the moving sash hooks a keeper on the frame or fixed sash. Styles include cam-action, lever and spring-loaded thumb latches.
• Casement multipoint or sash locks: a lever handle on the frame, often linked to a hidden tie bar that engages several keepers along the sash.
• Awning locks: similar to casement locks, usually a single lever or cam on each side.

Also note the material. Wood windows usually take universal surface-mount cam locks. Vinyl and aluminum windows often use manufacturer-specific locks with precise spacing, finishes and sometimes a custom profile, which is where most matching trouble begins.

Measure and Source a Matching Lock

Remove the old lock, if it is not already off, and measure these items with a ruler marked in 1/16-inch increments or a metric scale, since many locks are specified in millimeters:

1. Screw-hole spacing: center to center between the mounting holes. Common spacings include roughly 1-7/8, 2-1/16 and 2-1/2 inches, but many brand-specific locks fall in between.
2. Base length and width: so the new lock covers any paint lines or old holes.
3. Cam height: the distance from the bottom of the lock base to the underside of the cam. This must match the keeper height or the lock will not engage.
4. Handing: whether the lever turns left or right to lock. Many cam locks are reversible, but some are handed.
5. Screw type: length, diameter and whether they thread into a metal reinforcement inside a vinyl sash.

Look for a manufacturer name or number stamped on the lock, the glass spacer bar between the panes or a label on the frame. With a brand and approximate window year, a window parts supplier can usually match the part. Otherwise, take clear photos from the top and side next to a ruler and compare against parts catalogs. Universal window sash lock kits for wood windows often include several screw positions and a matching keeper.

Tools and Materials

• Replacement window sash lock and keeper, in the correct spacing, height and finish
• Phillips and flathead screwdrivers, including a stubby driver for tight spots
• Utility knife for cutting through paint around old hardware
• Tape measure or steel ruler with fine graduations
• Pencil, awl and a drill with small bits if new holes are needed
• Wood toothpicks and wood glue, or thin plastic shims, for stripped holes and keeper adjustments
• Rag and mild cleaner

How to Change Window Locks on Double-Hung Windows

1. Close the window fully. Push both sashes tight so the meeting rails align. Slide the lower sash all the way down and the upper sash all the way up.
2. Score paint. If the lock has been painted over, run a utility knife around the base to avoid tearing the finish.
3. Unscrew the lock. Remove the two screws and lift the lock off. Keep the screws in case the new ones are the wrong length.
4. Remove the keeper. Unscrew the keeper on the upper sash. Replace both parts together so the cam and keeper geometry match.
5. Clean the area. Wipe away dirt and old paint flakes so the new base sits flat.
6. Position the new keeper. Screw it loosely to the upper sash.
7. Install the lock. Set it on the lower sash, align with the existing holes and drive the screws snug, not overtight, especially in vinyl.
8. Test and adjust. Rotate the lever. It should draw the sashes together with firm but smooth pressure. Slide the keeper slightly if the cam rubs or misses, then tighten it.

Sliders and Casements

On sliding windows, remove the latch from the meeting rail of the moving sash, usually two screws on the face or edge. Some latches are held by screws accessible only when the sash is lifted out: open the window, lift the sash up into the top track and swing the bottom out. Get a helper for large sashes and support the glass, never flexing it. Match the latch to the existing keeper height and install in reverse order.

On casement windows, the lever handle mounts to the frame with two screws and connects to a tie bar. Open the window, unscrew the handle, unhook it from the tie bar and install the new one with the lever in the unlocked position so the bar engages correctly. If the tie bar itself is bent or worn, the whole multipoint mechanism may need replacement, which usually requires the manufacturer’s part.

Fixing Misaligned Keepers and Other Problems

Most lock complaints after replacement come from alignment, not the lock itself.

Cam will not reach the keeper: The sashes are not meeting tightly, often because the window is out of square or the balance system is weak. Check that the lower sash fully closes and the upper sash stays up. If it drifts down, the balances need attention. A thin shim under the keeper can raise it to meet a slightly low cam.

Lock is too tight or will not turn: The keeper is set too far in. Loosen it and shift it back 1/16 inch at a time.

Lock spins without pulling the sashes together: The cam height does not match the keeper, or the keeper is too far out. Confirm you bought the matching keeper.

Stripped screw holes: In wood, fill the hole with glued toothpicks, let dry, trim flush and redrive the screw. In vinyl, move up one screw size or use a slightly longer screw if a metal reinforcement lies beneath.

New holes don’t align with old ones: Choose a lock with a larger base that covers the old holes. On wood, fill old holes and drill small pilot holes. Avoid drilling vinyl or aluminum frames near reinforcement or drainage paths.

Security Upgrades, Costs and When to Call a Pro

Standard cam locks keep sashes tight and deter casual entry, but they are not strong security devices. For ground-floor or basement windows, consider adding keyed sash locks, sash stops that allow ventilation while limiting opening to about 4 inches, or window pin locks. Remember that bedroom windows used as emergency exits must remain openable without special knowledge or keys, so check local fire and building rules before installing keyed hardware there.

Universal cam locks for wood windows are inexpensive, generally a few dollars to around twenty dollars each, while brand-specific vinyl and casement hardware can cost more, especially for multipoint mechanisms. A handyman typically charges a modest service fee plus parts for several windows at once.

Call a window pro or the manufacturer when locks are part of a multipoint system built into the sash, when the sash is warped or the frame is out of square, when glass is cracked or the insulated glass has lost its seal, or when upper-story windows must be accessed from outside. Any work from a ladder on a second story is best left to a pro with proper equipment.