If a UPVC engineer tells you the gearbox needs replacing, you might be wondering what that actually means. The gearbox — also called a multipoint lock body or lock case — is the central component of a UPVC door's locking system. Here's what you need to know.
What Does the Gearbox Do?
When you lift the handle on a UPVC door, you're engaging the gearbox. It converts the movement of the handle into the simultaneous extension of multiple locking points — typically bolts at the top and bottom, hooks in the middle, and mushroom cams at intervals along the lock strip. This multipoint system is what makes UPVC doors significantly more secure than single-point locks.
How Does a Gearbox Fail?
Gearboxes fail gradually through normal wear. The most common symptoms are: the handle feels loose or flops down after use, the locking points don't extend fully when the key is turned, a grinding or clicking sound when operating the handle, or the door locking inconsistently. In some cases, the handle simply turns freely without engaging the mechanism at all.
How Is the Right Gearbox Identified?
UPVC gearboxes are not universal — they vary by handed (left or right hinge), case size (measured in millimetres), and backset (the distance from the edge of the door to the centre of the gearbox). Identifying the correct replacement requires measuring the existing unit and, where possible, noting the manufacturer. The Glass Guardian carries a comprehensive range and can identify the correct part on-site.
What Does Replacement Involve?
To replace a gearbox, the door furniture (handle, cover plates, letterbox) needs to be removed to expose the lock strip. The old gearbox is unclipped and the new one fitted and adjusted before reassembly. The whole process typically takes 60 to 90 minutes. Most gearbox replacements are completed on the first visit. The Glass Guardian provides this service across Birmingham and the Black Country.
Need a UPVC Repair in Birmingham or the Black Country?
The Glass Guardian provides fast, affordable UPVC window and door repairs across Birmingham, Dudley, Walsall, Wolverhampton, and the surrounding area. Call for a free quote.