1976 XJ12C rear window mechanisms designed by satan

My rear windows work for awhile, very slowly and then just stop all together. Is there a manual source for parts and repair instructions? It looks like I will need to remove the entire assembly of motor, window rails and gears.
Appreciate some advice.
Thank you,
Phillip

Removing the mechanism is not that hard, just get in there and do it.

There are adjustments that can be done on the rails and motor position that could help.
Lubricating the rails with graphite or silicone grease helps also.
But what would really make a difference is installing relays.
Aristides

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Aristides, you mention the best remedy is to install relays. Is the function of a rely to boost the charge at certain locations on the circuit or do they help maintain the original charge over a long distance? Excuse my ignorance, first time working on these windows.

Thank you

Phillip

Phillip,
I highly recommend that you get copies of the Jaguar Series 2 XJ6 Parts Catalogue and the Jaguar Series 2 XJ6 Repair Operations Manual.
I have learned that having the correct technical data about my Jaguars has taken a lot of the mystery (but not all.of the mystery) out of working on my Jaguars. The Parts Catalogue has lots of illustrations of the parts and is very helpful to understand how things are put together. The ROM is likewise very helpful in how to remove and replace components. These documents are not perfect, but I would be unable to keep my Jaguars looking and running their best without them.
I don’t have an XJ12C (although I wish I did) so I can’t be more specific about your current issue.

Paul

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You have a SI and I don’t know exactly how your electric windows are wired but at least on the SIII the power to the windows goes through the switches resulting in a very long back and forth of cables and a switch that often gets overloaded.
The end result is that the windows motors never see 12v, rather 9-10v if you are lucky.

With the relays you use the existing cables for the primary circuit, i. e. to drive the relays and you bring a nice and juicy new cable from the battery to drive the windows.
And if you put the relays as close to the windows as possible you will have minimal to zero loses.
I went somewhere in between and put them in the center console, it was the best compromise between function and having to take the whole interior apart…
The difference in the windows speed was very significant.
Aristides

Wow, exciting stuff. I have my work cut out for me. If this works as well as proclaimed, I owe you all a good bottle and a Cuban.
Thank you,
Phillip

PS, I will search for and purchase those two references.

I tried to upload the Series II XJ6 (1974 to 1979) electrical Guide to this post but the .pdf is too large. (over 3mb)

bob

Here’s one of the places I get in trouble with ever body.

My XJ12C had two non working mechanisms before I purchased the car. Finding replacements was pretty much a lost cause as the original design left a lot tombe desired, therefore a spare would likely be no better.

I sourced a kit for hot rods that had a motor attached to a cable and the cable end had a drive that I adapted to what was left of the working mechanism.

I later did the same to the doors.

Not original, but still works.

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It might pay to check the actual motor, I was using my S11 a few weeks ago in the rain and the wipers were decidedly reluctant to operate at any sort of regular speed (such as it is)
I investigated and this was what was inside;

A nice layer of carbon allowing tracking between segments

Phillip,

while Aristides’ advice is well taken, the original setup in SII cars did not make use of relays and in sedan configuration didn’t need them. Now the rear window mechanism in coupés is a different story, but I think you might just start with the regular ceremony: check (pull, clean, polish and lube) switches and contacts in the center console. BTW, there is also a window lift safety relay at the same place.

While there doesn’t seem to be any inline fuse, there are thermal breakers. They are a bit tricky as they give rise to works - doesn’t work scenarios. They are triggered by excessive load. So you might also lubricate all felt channels, if that applies to the coupé’s rear windows.

If you go into the lifting mimic the original description may help:


The motors seem to be quite solid pieces of engineering and seldom fail. Again I’d rather address contacts, in particular the ground path from the motors. From the wiring pattern it seems there is no ground wire at the window motors, but earth is provided via the fixing bolts of the motors. After 40+ years corrosion may have come in the way of an easy ground path and have led to the 9V scenario Aristides has described. So, again some cleaning, sanding, lubricating may be the easiest way to restore function.

Good luck

Jochen

75 XJ6L 4.2 auto (UK spec)

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**
The usual problem is, as Jochen says, the switches, Phillip - and it may pay to check that first…

If the windows themselves or the mechanisms are mechanically sticky; the thermal fuses will likely trip - denoting excessive current - stalled motors. If the switches are the problem; no/little current is flowing…

Frank
xj6 85 Sov Europe (UK/NZ)
**

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I have checked the switches and I am, at least getting juice to the motors. I will try to get a meter to test that current. Excuse my ignorance Frank but, are the thermal fuses you mention in the main fuse box under the left dash or are they in-line somewhere. Also, if I am getting juice to the motors, perhaps fuses are not the issue?
Thank you,
Phillip

Great stuff. Thanks Jochen
And thank you all for the excellent help.
Phillip

Phillip,

what Frank is getting at, as I understand him, is that it is not sufficient to have sufficient power at the motors to trigger a DMM or even a test light. The motors pull quite serious amperage, that is all lead through the switches - because there are no relays! That’s why it is crucial to reduce resistance at the contacts of the switches as much as possible. It is an easy clean hands job to pull the switches, remove them, polish the spade connectors, put some lubricant on and move the connectors a couple of times.

I’ve only just looked at the description I posted last night and it says “Smear grease in guide channels”. That sounds pretty much like fully gummed up channels in your car that the motors can’t handle, overheat and trigger the thermal breakers.

As for their location - I’m not sure whether I’m mixing things up - maybe they are located on the floor right at the base of the back seat and in the center of the car.

Good luck

Jochen

75 XJ6L 4.2 auto (UK spec)

**
The thermal fuses are located ‘somewhere’ under the dash, Phillip - but at this stage; it’s too early to access them.

The thermal fuses acts like ordinary fuses; excessive current heats them to break current flow. But while ordinary fuses burns off - the thermal fuses just resets after cooling down. A stalled motor draws very high current - and would burn out unless current is cut. Typically a motor may react and then stop as current is cut by the thermal fuse. Then respond again after a while; the sign of a functioning thermal fuse.

Measuring current draw is pertinent - a low current draw would indicate faulty connections or a failing motor. Which will not trip the thermal fuses, ie, if you are measuring voltage at a connected motor - constant voltage would imply low current flow.

As a side observation; low current due to resistance will cause heating up of the relevant place…

Frank
xj6 85 Sov Europe (UK/NZ)
**

Thank you Jochen, I will take a look for those breakers. However, if I am getting at least some juice at the motors, perhaps the breakers a not the problem?
Thanks again.
Phillip

Correct. The thermal breakers will interrupt the circuit at a given temperature and automatically close it upon cooling down. Not an ideal setup for fault finding …

In order to check the motors you might make a direct connection - ideally fused - from the battery.

Good luck

Jochen

75 XJ6L 4.2 auto (UK spec)

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If you get some juice in the motors it means you have power and that the circuit is complete.
Now, how much of a juice they get is an other story…
I suggest you get a pair of good size cables directly from the battery, or any 12V-10A power source, connect them directly to the windows motors and see what happens. This will tell you if the motors are good enough and you will see how much juice you loose with the original configuration.

Another cause of slow windows is the channels. They have a velvety overcoat to help the glass slide.
If this coat wears then the glass is running on rubber and starts to bind.

Aristides

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Had a chance to get back on the rear windows in my coupe. It appears that the slow (at best) window operation is more mechanical than electrical. I have cleaned and well lubricated the sliding components, cleaned and sanded to bright all electrical connectors and lift motor to cabin mounting surfaces and have removed the lift motor and cleaned and sanded to bright metal the mounting surfaces.
In trying to re-install the lift motor, I now realize that the lifting arm must be in a particular position to allow the motor to be mounted again to the cabin housing. That brings me to my current frustration. The photo attached shows a lift motor and attached lifting arm, etc. My question is: there is a small set screw located at the end of the worm screw that is operated by the motor and which activates the lift arm gears. What is the function of this set screw?
I am most anxious to get this back together and see if my efforts have been successful but I wanted to find out the function of this important looking set screw before installing the motors.
Thank you all so far for the wonderful advice.
Phillip

It is a thrust point for the motor shaft, it shouldn’t require any adjustment.

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