Why Is My Window Gearbox Stiff? Common Causes and Fixes

Why Is My Window Gearbox Stiff? Common Causes and Fixes

A stiff window gearbox is a frequent problem on uPVC and aluminium casement windows and tilt-and-turn units; it affects operation, security and can hasten component wear. Whether you are a homeowner wanting a quick DIY fix or a trade professional diagnosing recurring faults, this post explains the common causes, practical checks and repairs for a stiff window gearbox.

What a window gearbox does and where stiffness shows

The window gearbox converts the rotational movement of the handle into the linear travel of an espagnolette rod or locking cams. When it becomes stiff you will notice heavy or jerky handle operation, incomplete locking or the handle returning to a different position. Modern gearboxes are often made of plastic with metal internals; over time these parts can bind, strip or corrode.

Common causes of a stiff gearbox

Most stiffness issues come from five main sources:

• Lubrication failure: grease has dried, washed out or become contaminated; parts seize or drag.
• Debris and corrosion: dirt, salt or rust in the gearbox, slot tracks or keeps causes friction.
• Worn or damaged gears: plastic gear teeth can strip; metal gears can wear unevenly.
• Binding elsewhere in the window: misaligned hinges, swelled timber sashes or distorted seals can put extra load on the gearbox.
• Incorrect installation or geometry: wrong spindle size/backset, misaligned espagnolette rod or loose fixings.

Quick checks you can do now

Before dismantling anything try these simple checks; they often reveal the cause.

• Operate the handle slowly and listen: grinding suggests debris or worn teeth; a heavy, but smooth, feel often points to lubrication problems.
• Check the lock keeps and striker plates: loose or misaligned keeps cause poor engagement and extra load on the gearbox.
• Inspect the hinges and stays: binding here transfers force to the gearbox; open the window fully and see if the sash moves freely.
• Look for visible corrosion or broken teeth at the gearbox cover; remove any trim caps to get a quick view.

DIY fixes: lubrication and simple adjustments

For homeowners the two most likely fixes are lubrication and adjustment of keeps; both are straightforward.

• Tools and materials: silicone spray, PTFE spray or white lithium grease; a cloth; a small brush; screwdriver set and hex keys as required.
• Remove handle and check spline: most handles pull off after a grub screw is loosened. Inspect the spindle for wear and ensure the handle slides on correctly.
• Lubricate moving parts: apply a light coating of PTFE or white lithium grease to the gearbox spindle, the point where the espagnolette rod engages and the striker plates; avoid over-oiling as excess attracts dirt.
• Avoid using penetrating oil like WD-40 as a long-term lubricant; it displaces grease and can dry out components. Silicone spray is acceptable on uPVC and seals but does not last as long as a dedicated PTFE or lithium grease.
• Adjust keeps and striker plates: slacken the screws, align the keep so the locking cam meets it squarely, then re-tighten. On multipoint systems also check the top and bottom keeps; small adjustments can remove binding.

When deeper inspection or gearbox replacement is needed

If lubrication and keep adjustment do not restore smooth operation, the gearbox may need to be removed and inspected or replaced. This is a common trade job but can be done by competent DIYers with patience.

• Access the gearbox: remove handle and the trim or cover plate to expose the gearbox. Some systems require removing the sash or sliding off bead covers for access.
• Check for stripped gears, cracked plastic housing or a rounded spindle: these are replacement indicators.
• Remove the gearbox: undo retaining screws (often Torx or cross-head), withdraw the gearbox and inspect the espagnolette rod engagement and cam pins.
• Replace with a matching unit: ensure the new gearbox has the correct spindle size (commonly 7mm or 8mm square), backset and mounting hole positions. Test-fit before final assembly.
• Reassemble and lubricate: transfer any cams or retaining clips and use suitable grease on moving faces; test the handle through its full travel before returning trim.

Trade tips for durable repairs

For installers and window repair specialists these practices reduce call-backs and prolong component life:

• Replace plastic gearboxes proactively on older uPVC units rather than repairing stripped teeth; the cost and time saved in repeat visits is worth it.
• When fitting new gearboxes also renew or check espagnolette rods and striker keeps; mismatched components defeat a new gearbox.
• Use long‑lasting greases: white lithium or specialised window gearbox greases resist washout and maintain smooth action.
• Record the spindle size, backset and manufacturer code; many replacement parts are brand specific and not interchangeable.
• Check the whole window geometry: sash drop due to worn hinges often presents as gearbox stiffness; replacing hinges or adjusting friction stays can be the correct remedy.

When to call a professional

Call a qualified window engineer if:

• There is visible damage to gears or the espagnolette rod; or the gearbox continually strips after replacement.
• The sash is sagging, heavily swollen or the frame is distorted; these structural issues need specialist intervention.
• Security is compromised and you need immediate, certified repair.
• You are unsure how to source the correct replacement gearbox; trade parts sourcing and identification are faster for professionals.

Further reading and parts

For more detail on espagnolette rods, keeps and compatible gearboxes see our pillar resource on espagnolette window locks: /guides/espagnolette-window-locks. If you need parts we supply a wide range of replacement gearboxes, spindles and keeps; consult product codes to match existing hardware.

Recommended Products

Based on this article, you may find these products helpful:

• Top Hung Friction Stay - 12"
• ERA Egress (Fire escape) Friction Stay
• TSS Standard Friction Stays – 13mm & 17mm Stack Height
• Restricted Friction Stay Hinges
• ERAB Espagnolette Window Lock Universal Lock Replacement

Conclusion and next steps

A stiff window gearbox is usually caused by lack of lubrication, debris, worn gears or binding elsewhere in the window. Start with simple checks: lubricate with a PTFE or white lithium grease, inspect and adjust keeps, and check hinges for binding. If the gearbox shows stripped teeth or cracked housing replace it with a matching unit and ensure correct spindle and backset. For complex sash alignment issues or repeated failures call a professional window engineer.

If you want specific parts or a step‑by‑step parts list for your make of window, contact our trade desk or browse replacement gearboxes and espagnolette components on the Window Hardware Store site.