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There are three basic systems used to raise and lower car windows: mechanical linkage with scissor action; cable and pulley; or rack and pinion.
No two manufacturers use exactly the same design for window-lifting systems of the same basic type. Details vary from car to car.
If you need to fit a new mechanism because of accident damage, breakage or wear on the old one, obtain the correct replacement from the spares department of a main dealer for the car.
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Renewing a link-type mechanism
Fully close the window and tape the glass to the top of the window frame. Use strong tape, as this must hold the glass to prevent it dropping when the mechanism is removed.
Take off the door fittings and trimmings and the inner door panel (See Removing a door trim panel). Carefully remove the polythene condensation-barrier sheet behind the panel and set it aside for reuse.
Undo and remove the screws holding the toothed regulator to the door frame and put them in a safe place. Push the regulator into the door interior.
Reach through the door access aperture to disconnect the sliding arm. It may fit into a bottom channel, or it may be held by a centre pivot secured by three screws.
After disconnecting the sliding arm, move the regulator and the arm sideways in both directions until the upper end comes away from the sliding channel at the bottom of the glass. Lift out the mechanism through the access aperture.
Before fitting the new mechanism, grease the pivot and sliding bearings, and the gear teeth on the regulator. Lightly smear the whole mechanism with petroleum jelly which will act as a protection against rust.
To refit the new assembly, which includes the regulator and sliding arm, follow the removal procedure in reverse. Retape the polythene sheet in position. Test the mechanism before refitting the door panel and trim.
Adjusting a cable-and-pulley window winder
The cable may slacken after long use, causing play in the winder mechanism as the handle changes direction between up and down. Adjusting a pulley to take up the slack in the cable will correct the fault.
Take off the door fittings and trimmings and the inner door panel, including the polythene condensation-barrier sheet (See Removing a door trim panel). Check the condition of the cable; even if it is only slightly frayed, it must be renewed. If not frayed, it can be adjusted.
Look for the adjustable pulley, which slides sideways on a mounting in the door frame to alter the cable tension.
Loosen the pulley mounting and move it to take up the slack in the cable. Retighten the mounting and check that the winder action is smooth. If necessary, readjust the pulley until it is. Take care not to over-adjust, which will strain the cable and regulator.
If the cable is broken or frayed and needs renewing, you will probably have to buy it as part of a complete assembly with a new regulator.
There are different assemblies for right-hand doors and left-hand doors. Make sure you buy the correct one.
To fit a new cable, take the cable clamps off the bottom of the window glass, push the window closed, and tape it to the top of the frame.
Undo the fixing screws to remove the regulator and cable drum, and the cable.
Slacken the adjustable pulley. Screw the new regulator and its loop of cable in position.
To wind the cable on to the grooves of the cable drum, take the length fixed to the drum on the side nearest to the middle of the car. Loop it round the furthest bottom pulley.
Fit the winder to the regulator and drum. Keeping the cable taut, wind it on to the drum. Turn the winder anti-clockwise on a right-hand door, clockwise on a left-hand door.
Take care that the spare part of the cable does not wrap round the drum, and wind until all the grooves in the drum are filled and the upper part of the cable is vertical.
Keeping the cable taut, loop it round the rear upper pulley, the front lower pulley, and the front upper pulley. Make sure it does not kink.
Tension the cable by moving the adjustable pulley. Oil the pulley spindles with engine oil, and grease the cable.
To re-attach the window glass to the mechanism, wind the cable fully down, then up again one full turn of the winder. Some regulators have an indicator to mark the point. Untape the glass, lower it fully and re-clamp it to the cable.
Test the winding action several times. If the glass does not move up and down smoothly, reposition it on the cable until it does. Replace the polythene sheet and refit the door panel and trim.
Replacing a rack-and-pinion system
Take off the door fittings and trimmings and the inner door panel, including the polythene condensation-barrier sheet.
Wind the window down until you can undo the plate holding the glass to the rack. Push the glass to the top of the frame and secure it with tape.
To remove the rack, undo the screws at its top and bottom and at the winder-handle boss.
The bottom screws of the rack may be on the underside of the door. Lift out the rack and winder boss through the access aperture.
Grease all the moving parts of the new rack assembly before fitting.
Position the handle-fixing holes on the boss to align with the winder handle. Refit the handle and wind the mechanism fully down. Untape the glass and refit it on the rack.
Check that the glass moves smoothly up and down. If not, adjust its position on the rack until it does.