Door Lock Gearbox - Truly PVC Limited - Mark 1

These locks typically have a more substantial, older design compared to modern systems. They often feature a split-spindle mechanism and were common on uPVC doors manufactured before the mid-2000s. The best way to confirm is by visually comparing your existing gearbox with images of the Mark 1 GU Ferco gearbox or by checking the manufacturer's original door documentation if available.

The backset is the distance from the edge of the door to the center of the large spindle hole (where the door handle goes). To measure, remove your door handle and lock mechanism, then measure from the door's edge straight across to the center of the hole. This gearbox is available in 30mm and 35mm backsets.

PZ (or P.Z.) stands for the 'center to center' measurement between the spindle hole for the handle and the keyhole. This gearbox uses a standard 92mm P.Z. measurement, meaning the distance from the center of the handle spindle hole to the center of the keyhole is 92mm. Most modern and many older lever handles will be compatible.

Yes, this gearbox features universal handing, meaning its sprung latch can be easily reversed or is designed to work correctly regardless of whether the door opens inwards or outwards, left-handed or right-handed.

You will typically need a Phillips head screwdriver and potentially a flathead screwdriver for leverage or prying. A tape measure is also essential for confirming the backset and P.Z. measurements before purchasing.

This product is a replacement gearbox and usually includes the necessary screws to secure the gearbox itself within the lock case. However, it does not typically include screws for reattaching the door handles, as these are usually part of the handle set.

If the lock is seized due to a faulty gearbox, this replacement is likely to fix it. However, if the lock is seized due to damage to the lock case, bolts, or internal mechanism beyond the gearbox, further repairs or a full lock replacement may be necessary.

Ensure the spindle from the door handle is fully inserted into the gearbox and that the handle fixing screws are tightened securely. Check that the P.Z. measurement of your handle matches the 92mm standard of the gearbox.

Confirm the gearbox is correctly seated within the lock case and that all screws are adequately tightened without over-tightening. Ensure no part of the door or frame is obstructing the bolt or latch. Lubricate the mechanism with a light silicone spray.

Double-check that the correct backset gearbox (30mm or 35mm) was installed. Ensure the gearbox is correctly aligned within the lock case and that the door is not sagging or misaligned in the frame, which could prevent proper bolt extension.

Verify that you are attempting to install this gearbox into the correct 'Old Style' Mark 1 GU Ferco lock. Ensure the backset measurement (30mm or 35mm) is correct for your door. Minor adjustments to the lock case or door might be needed in rare cases if the door hardware has shifted over time.