90 convertible top window operation

Does anyone know the timing logic of the rrear window operation? When mine travel down they run too long and motor drive gear and window regulator gear become wedged together. I must remove trim panel and from above use a long flat screwdriver between gears, twist and free them up. Going back up is no problem. Motors have been rebuilt. What the heck??? Thanks.

There are adjustment you can make to the window on how high/Low the window goes. You can also adjust the Tilt of the window. I believe those adjusters are on the very bottom of the regulator.

I believe that the details of how to adjust the convertible rear windows can be found in the Jaguar XJ-S Repair Operations Manual (ROM).


Thanks guys. I will look at that. I wonder how the run time duration is controlled.

Never had opportunity to work on power windows in XJS but every power window setup I have messed with have had an adjustable stop at end of travel. Is there a possibility the stop needs adjustment or is missing.

Paul. Do you have an image of your wife’s car with the top down? I’m wondering if I need to set the motor drive gear one tooth higher. I’m curious as to how high the window should be when retacted. Thanks, Dave.

Attached are pictures of the left and right rear windows retracted in my wife’s 1990 XJ-S convertible with the top down and the tan vinyl hood cover on. I am not sure how much this will help you since I bypassed the automatic rear window features in this car many years ago and installed switches to control the rear windows. So the rear windows in this car go up and down whenever we want them to and they are raised and lowered to whatever position we want when we want. I have posted about this modification many times. It is the most useful modification that I have made to this car since we raise and lower the convertible top all year long here in southern California and sometimes multiple times each day.

So I don’t know how much the window height means since they were not lowered automatically to that position but lowered there through the use of the switches that I installed.


Thanks Paul. What stops them at the upper and lower limits? Do they trigger the thermal switch when they have no more travel room? Mine drive down to far and bind before thermal protection can shut them down. They seem to be adjusted fine and match door window height when up and look similar to yours when down. These have been a sore spot on this car for the 10 years I’ve owned it. I’ll never be bored with this car. Dave.

Sorry, but I don’t know what limits the travel of the rear windows for certain. It is very likely a mechanical stop as Wayne mentions.
The flaky rear windows were a sore spot with my wife and me as well. I tried everything that I could think of including testing and swapping the relays, removing disassembling and cleaning the window motors, and making every adjustment that I could, but they remained flaky and unreliable. I gave up on the automatic rear windows and installed the switches. We never think about the rear windows now. They always do what we want them to do, always. Top up and windows down, no problem. Top down and windows up, no problem. One window up the other one down, no problem. One or both windows partially open, no problem. Jaguar made the automatic rear windows in the convertible too complicated and they are not reliable enough for me. I installed the switches in 2007 and after over 13 years they still work every time.


I do. Mechanical stop.

Of note: If you have a 1990 XJ-S convertible, your rear window motors are what we refer to as the “square case Delco”. They are garbage, not to put too fine a point on it. If you have any grief from them whatsoever, it is recommended you replace them with the Bosch motors used in the 1992-on convertible. It’s a bolt-in swap – although that particular bolt-in job is no picnic.

Kirbert, thanks for your reply. I’m trying to learn what controls the run time duration. When traveling down they run too long perhaps and motor drive gear wedges with regulator gear so they will not run up on the next cycle. Not a motor problem. It seems to me a run duration issue or maybe I need to reposition drive gear on regulator to allow for less downward travel. I suppose timing is controlled via control module. Dave.

Yep, motor problem. They are supposed to run hard against the physical stop, and then readily pull away when reversed. If yours doesn’t, there’s a problem in the motor assembly. There’s some sort of damper or whatnot that’s supposed to protect the glass from shocks, and it’s probably gone bad and is jamming.

A bit more detail on that Bosch upgrade. The regulators are virtually unchanged, so you can readily replace the Delco motor and regulator with the Bosch motor and regulator. Whether you can replace just the motor is an open question. It looks like you can – both motors mount similarly and both utilize a 14-tooth pinion – but there might be a difference in the motor mounting holes. Can be fixed with a bit of drilling or grinding? Unknown. In place? Doubtful, you’d probably need to get the regulator out to work on it, a definite PITA.

The reason this is important: The regulator is probably unique to the Jaguar convertible, but the same Bosch motor is used in scads of other cars, sometimes with the same 14-tooth pinion and sometimes with smaller pinions. Which makes it easier to locate replacement motors. The Mercedes W123 is known to use the same motor with the 14-tooth pinion.

Since making this mod to the back windows, any problems with them not going down. My car is a 89 conv


Since I added the rear windows switches in my wife’s 1990 XJ-S convertible in 2007 (over 13 years ago) we no longer had the problems with the rear windows going up or down. The switches are independent of the automated convertible top, so we can raise and/or lower them as we please just like the ones in the front doors. One of the windows is a little slower than the other to go up and down, but with the switches that is not a problem. I suspect that if I reverted back to the original automated system (which I would never do) that window might not raise and lower completely.


I did my 91 the same as Paul , using his directions. Also one of the best easiest mods.

Cathies 1991 had the right rear quarter window “down-only” syndrome for years. I repaired it. The problem was a weak motor which was fine in gravity mode but couldn’t raise it.

The motor brushes were badly worn. I had a NOS Delco motor and took it apart and swapped the brushes to the original.

I also used the NOS Delco motor case. The new armature had a different worm gear thickness. I attempted to use that also but since the internal gearcase gear did not mate properly it had intermittent operation. Swapped the original armature back in after cleaning the commutator.

I ran through a dozen or more top down up cycles and now works fine.

PS will add details, photos and videos later

Here is the process I used to repair the RR Quarter window. The problem was that it would go down but hardly ever raise during the top-up cycle.

After removing the regulator assembly I tested it on the bench. Here you can see that the motor lacked the needed torque to raise it and was a internal motor issue.


After the repair further repeated bench test showed it was fixed.


Here is a sequence of photos showing the repair. I salvaged the brushes from the GM NOS motor and replaced them into the original Jaguar motor and all was fine. After installing back in the car I ran over a dozen down-up cycles over a 15 minute period. The quarter window worked flawlessly. Weeks later I ran cycles again and all was good.


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I would still like to learn/understand exactly what turns off the power at the end of a up or down run cycle. The thermal protection switch should open if motor is overloaded. I have no idea as to control module programming. Motor runs hard against stops and drive gear wedges against regulator gear. Plenty of power in the motor to cause this binding. Seems like they run too long in either direction. Regulator gear actually bends outward and drive gear tucks under, wedges and then I assume that thermal switch opens or power is removed via programmed time run in module. ??? Still stumped.