WHAT GOES WRONG

Stiff movement

Lubricate the rubber-and-felt channels with silicone spray, silicone oil or silicone grease. If the glass still doesn’t slide up and down easily, adjust one or both channels. First, remove the doorcard.

Channel adjustment

Oval slots in the door frame allow channel adjustment. There should be one at the top and one at the bottom. Tweak them until the glass is snug – but not pinched – at both extremes of its travel.

Glass drops into door

If the glass drops down, the rollers of a crank mechanism may have come out of their channels. Cable-type: the wire may have broken or come off its pulleys – or the cable clamps have come loose.

Rattling glass

If the glass rattles or clatters against the door frame when wound partially down, try adjusting the channels. It may, however, be due down to worn, rotten or split rubbers, which will need replacing.

Stiff mechanism

If stiffness is not due to channel adjustment, lubricate the mechanism with oil or penetrating oil. Apply grease – which will resist being washed off by rainwater – when everything is working smoothly.

Grinding mechanism

This can be due to wear or disintegration of riveted parts of the mechanism (replace with nuts, bolts and spacers). A cable may have jumped off a pulley and be sawing through the spindle.