Easy down and up on the Stag

After working on the Jaguar window regulators, now was time to investigate the slow operation of the Stag passenger window. It was proving more difficult to open than close which seemed strange, and had recently got worse so that you could only fully open the window with the engine running so that the alternator was charging at 14 volts. The investigation revolved around checking the performance of the regulator and the motor, the wiring and movement of the glass in the frame, so the first task was to remove the door trim to access the internals.

The quarterlight control knob and door handle escutcheon were removed, followed by the one screw in the centre of the armrest that secures it to the door frame – both ends of the armrest are fixed to the trim panel and not attached to the frame. The complete panel and armrest could now be removed by feeding a wide blade behind the panel and gently levering the trim away from the frame to release the spring clips. After working around the panel like this and releasing all the clips, the panel could be lifted so that the top came free, then disconnecting the connectors on the wiring to the puddle light enabled the panel to be removed. The polythene sheet between the frame and panel was detached on the sides and base so it could be rolled up to give access to the internals.

The first item to check was the voltage at the motor during the window operation to ensure that there was not an excessive drop. Disconnecting the motor plug and changing the wiring allowed a volt meter to be connected. With no load the voltage was very close to that of the battery, but it dropped a couple of volts when the window was operated, which was as expected.

For further investigation, the motor and regulator required removing from the door, so after using duct tape to hold the window glass in place, the four regulator securing set screws were removed and the regulator and motor disconnected from the glass and lowered to the bottom of the door.

I tried to remove the motor from the door, but it soon became obvious that the bottom legs of the window frame and their respective mounting brackets were making

this impossible, so the window frame required removal. However, prior to doing this the tape was pulled from the glass and the window manually raised and lowered to ensure it was free to slide in the frame. After I was satisfied that there was little resistance, the tape was reapplied.

The window frame is held in position by five bolts, three along the top edge and two at the bottom of each leg of the frame that fit onto brackets. After all bolts were removed and the quarterlight gearbox detached, the frame and glass could be eased out of the top of the door. The regulator was then removed, clamped in the vice and connected to a 12v switched supply – an operational check confirmed that the torque on the regulator arm appeared OK in both directions. I thought it best to still strip the motor to check the internals though, taking care when removing the motor from the regulator arm as there was tension on the coil spring. With the mounting plate secured, the regulator arm could be held during the motor removal, then unwound to release the tension.

The two motor end cover retaining screws were undone, allowing the motor to be disassembled. All the internals seemed fine, with no burning marks on the commutator which was in good condition and the brushes were free in their guides. So there were no obvious problems with the motor, which really confirmed the result of the earlier operational test on the complete assembly. After a clean, the motor was reassembled and reunited with the regulator, although the coil spring was repositioned by 180° on the centre peg so that it had less tension, which would result in less motor power required to open the window – I just hoped that the motor could still close the window.

I also looked for other possible issues and found that the track along the underside of the glass that the regulator arm bush locates in was out of line with the glass, which may have resulted in excessive friction. At this point I remembered that when I was restoring the car, I had found that the regulator arm nylon bush was missing and a strip of wood had been wedged between the glass and door bottom to permanently hold the window in the closed position. It now seems feasible that the track was bent during the fitting of this wood, and I missed it at the restoration. The channel was therefore realigned with the window glass in the hope that this would allow the regulator bush to slide along the channel with less resistance and improve window operation.

Unfortunately there was no way of testing this theory without refitting the regulator, glass and frame. So next the regulator and motor were positioned in correct orientation in the bottom of the door, the window frame was replaced and the three top locating set screws loosely fitted, then the motor was operated to get the regulator in the correct position so it could be connected to the window and loosely bolted in position. The two brackets were fitted to the base of the frame, the motor wiring connected and the window operation checked.

Success – the glass moved smoothly up and down with just battery voltage. The top window securing bolts were nipped up and the lower frame legs adjusted on their brackets so that the frame seated against the hood, A and B-posts when the door was closed. All bolts were then tightened and the internal trim replaced, before a final check confirmed that window operation was now much smoother.

“The glass moved smoothly up and down with just battery voltage”

Internal door trim removed so motor voltage could be checked with and without the motor running.

Glass was secured with duct tape prior to unbolting the regulator.

Mike concluded that the misalignment of the track seen here was a contributor to the slow operation of the window.

Job done – trim replaced and the puddle light operational.

Here on the workbench, the motor was removed from the window regulator mechanism for further investigation.

There were no issues with the motor internals. Note the wire loop holding the brushes in place for replacing the armature.

This is the piece of hardwood that was jammed in the door frame to hold the window closed – it was so tight that it had to be cut prior to removal.